Mechanical, Thermal, and Electrical Properties of Graphene

Mechanical, Thermal, and Electrical Properties of Graphene
polymers
Review
Mechanical, Thermal, and Electrical Properties of
Graphene-Epoxy Nanocomposites—A Review
Rasheed Atif, Islam Shyha and Fawad Inam *
Department of Mechanical and Construction Engineering, Faculty of Engineering and Environment,
Northumbria University, Newcastle upon Tyne NE1 8ST, UK; [email protected] (R.A.);
[email protected] (I.S.)
* Correspondence: [email protected]; Tel.: +44-191-227-3741
Academic Editor: Antonio Pizzi
Received: 11 June 2016; Accepted: 25 July 2016; Published: 4 August 2016
Abstract: Monolithic epoxy, because of its brittleness, cannot prevent crack propagation and is
vulnerable to fracture. However, it is well established that when reinforced—especially by nano-fillers,
such as metallic oxides, clays, carbon nanotubes, and other carbonaceous materials—its ability to
withstand crack propagation is propitiously improved. Among various nano-fillers, graphene has
recently been employed as reinforcement in epoxy to enhance the fracture related properties of
the produced epoxy–graphene nanocomposites. In this review, mechanical, thermal, and electrical
properties of graphene reinforced epoxy nanocomposites will be correlated with the topographical
features, morphology, weight fraction, dispersion state, and surface functionalization of graphene.
The factors in which contrasting results were reported in the literature are highlighted, such as the
influence of graphene on the mechanical properties of epoxy nanocomposites. Furthermore, the
challenges to achieving the desired performance of polymer nanocomposites are also suggested
throughout the article.
Keywords: mechanical properties;
epoxy; nanocomposites
thermal properties;
electrical properties;
graphene;
1. Introduction
Polymer Matrix Composites (PMCs) have found extensive applications in aerospace, automotive,
and construction, owing to ease of processing and high strength-to-weight ratio, which is an important
property required for aerospace applications [1]. Among different polymers, epoxy is the most
commonly used thermosetting polymer matrix in PMCs [2]. The damage tolerance and fracture
toughness of epoxy can be enhanced with the incorporation of (nano-) reinforcement, such as metallic
oxides [3–5], clays [6–8], carbon nanotubes (CNTs) [9–11], and other carbonaceous materials [12–14].
After the groundbreaking experiments on the two-dimensional material graphene by Nobel Laureates
Sir Andre Geim and Konstantin Novoselov [15] from the University of Manchester, graphene came into
the limelight in the research community, mainly because of its excellent electrical [16], thermal [17], and
mechanical properties [18]. Graphene found widespread applications in electronics [19], bio-electric
sensors [20], energy technology [21], lithium batteries [22], aerospace [23], bio-engineering [24], and
various other fields of nanotechnology [25]. There is an exponential rise in the use of graphene in
different research areas, mainly because of the properties inherited in, and transferred by, graphene to
the processed graphene-based materials.
To summarize the research trends related to graphene-based nanocomposites, multiple review
articles were recently published in which various aspects of graphene-based nanocomposites were
discussed. There are numerous ways to produce and characterize graphene-based materials [26].
Graphene-based materials were studied for different properties, such as thermal properties [27],
Polymers 2016, 8, 281; doi:10.3390/polym8080281
www.mdpi.com/journal/polymers
Polymers 2016, 8, 281
2 of 37
mechanical properties [28], electrical properties [29], rheological properties [30], microwave
adsorption [31,32], environmental and toxicological impacts [33], effect of preparation [34], and
gas barrier properties [35]. These materials have found biological applications, especially related
to toxicity [36], and in other applications like electrically-conductive adhesives [37] and selective
photoredox reactions [38]. Because of their hierarchical pore structures, these materials were found
suitable for gas sorption, storage, and separation [39]. Various factors influence the mechanical
properties of graphene-based materials—e.g., γ-ray irradiation was found to have a strong influence
on the structure–property relationship [40]. Various theoretical models were developed to predict
the mechanical properties of epoxy–graphene nanocompsites and correlated with interphases and
interfacial interactions [41]. It was presented that continuum mechanics can be used to predict the
minimum graphene sheet dimensions and optimum number of layers for good reinforcement [42].
Graphene was compared with other reinforcements, such as clays [43] and CNTs [44], and was shown
to have properties superior to the other nano-fillers. Various surface modifications were employed to
improve interfacial interactions, and their influence on the performance of polymer nanocomposites
was studied [45].
To date, eclectic reviews on graphene composites are covering a broad range of graphene-related
issues; it can, however, be observed that there is an obvious gap in the lack of a review article discussing
the mechanical, thermal, and electrical properties of epoxy–graphene nanocomposites. Therefore, this
review article discusses the correlation between graphene structure, morphology, weight fraction,
dispersion, surface modifications, and the corresponding mechanical, thermal, and electrical properties
of epoxy–graphene nanocomposites.
2. Epoxy as Matrix
There are various types of epoxy which have a wide range of applications because of their
superior attributes, such as improvement in composite mechanical properties, acceptable cost, and
processing flexibility [2]. Phenolic glycidyl ethers are formed by the condensation reaction between
epichlorohydrin and a phenol group. Within this class, the structure of the phenol-containing molecule
and the number of phenol groups per molecule distinguish different types of resins and the final
properties of monolithic epoxies and nanocomposites [2]. The epoxies have found some “high-end”
applications, including aerospace, marine, automotive, high-performance sports equipment (such
as tennis rackets), electronics, and industrial applications [46]. Due to the superior properties of
carbonaceous materials, such as high strength and stiffness, they are most widely used at present as
reinforcement in advanced Epoxy Matrix Composites (EMCs) [47–50].
Epoxy resins are of particular interest to structural engineers because these resins provide a unique
balance of chemical and mechanical properties combined with extreme processing versatility [51].
When a composite is produced from epoxy-carbon using hand lay-up process, a great flexibility
in aligning the fraction of fibers in a particular direction is available, which is dependent upon
the in-service load on the composite structural member. In-plane isotropy can also be achieved by
stacking the resin-impregnated fiber layers at equal numbers of 0˝ , +45˝ , ´45˝ , and 90˝ . There are
also other stacking sequences that can be used to achieve in-plane isotropy. The specific stiffness
of quasi-isotropic epoxy–graphite laminated composite is higher than many structural metals. The
highest specific strength achieved in epoxy–graphite is higher than common structural metals, with
the exception of ultrahigh-strength steels and some β-titanium alloys. For example, the epoxy-carbon
crutch is 50% lighter and still stronger than the aluminium crutch [2].
3. Graphene as Reinforcement
Graphene—a densely packed honey-comb crystal lattice made of carbon atoms having a thickness
equal to the atomic size of one carbon atom—has revolutionized the scientific parlance due to
its exceptional physical, electrical, and chemical properties. The graphene now found in various
applications was previously considered only a research material and a theoretical model to describe
Polymers 2016, 8, 281
3 of 37
the properties of other carbonaceous materials such as fullerenes, graphite, Single-Walled Carbon
Nanotubes (SWNTs), and Multi-Walled Carbon Nanotubes (MWNTs). It was believed that the real
existence of stand-alone single layer graphene would not be possible because of thermal fluctuations,
as the stability of long-range crystalline order found in graphene was considered impossible at finite
(room) temperatures. This perception was turned into belief by experiments when the stability of
thin films was found to have direct relation with the film thickness; i.e., film stability decreases with
a decrease in film thickness [52]. However, graphene can currently be found on a silicon substrate
or suspended in a liquid and ready for processing. Although its industrial applications are not
ubiquitous, it is widely used for research purposes (e.g., as reinforcement in PMCs) and has shown
significant improvement in different (mechanical, thermal, electrical etc.) properties of produced
nanocomposites [52–56].
The ability of a material to resist the propagation of an advancing crack is vital to the prevention
of failure/fracture [57]. Graphene can significantly improve fracture toughness of epoxy at very low
volume fraction by deflecting the advancing crack in the matrix. The details of the influence of various
kinds of graphene/graphite nanoplatelets (GNPs) on the fracture toughness of epoxy nanocomposites
are listed in Table 1. In all the composite systems mentioned in Table 1, epoxy was used as matrix
and the nanocomposites were produced using solution casting technique, except [58] where the resin
infiltration method was employed. The incorporation of graphene in epoxy can increase its fracture
toughness by as much as 131% [59]. It can also be observed that graphene size, weight fraction, surface
modification, and dispersion mode have strong influence on the improvement in fracture toughness
values of the produced epoxy–graphene nanocomposites. Monolithic epoxy shows brittle fracture and
beeline crack propagates, which results in straight fracture surfaces. The advancing crack in epoxy
interacts with the graphene sheets. Initially, the crack propagates through the epoxy matrix as there
are no significant intrinsic mechanisms available in monolithic epoxy to restrict crack propagation.
However, no sooner than the crack faces strong graphene sheets ahead, it surrenders and subdues.
Nevertheless, the extent of matrix strengthening and crack bridging provided by graphene strongly
depends upon its dispersion state and interfacial interactions with the epoxy matrix [60,61].
4. Fracture Toughness
The successful employment of epoxy-based nanocomposites relies on the ability of the composite
system to meet design and service requirements. The epoxy-based nanocomposites have found
applications in aerospace, automotive, and construction due to ease of processing and high
strength-to-weight ratio. In many applications, the composite system undergoes external loadings.
The relationship between loads acting on a system and the response of the system towards the
applied loads is studied in terms of mechanical properties. Therefore, epoxy-based nanocomposites
are supposed to have superior mechanical properties. There are various tests to measure mechanical
properties, such as tensile testing, bend testing, creep testing, fatigue testing, and hardness testing,
to name a few. These tests usually take specimens of specific geometries and subject to loading at
certain rate. In general, the industrial scale samples contain porosity and notches which act as stress
concentrators and are deleterious to the mechanical properties of nanocomposites. Sometimes, it
becomes difficult to control the maximum flaw size. The shape of the flaw is another very important
parameter, as pointed notch (V-notch) is more detrimental than round notch (U-shaped) [62].
Polymers 2016, 8, 281
4 of 37
Table 1. A brief record of epoxy-based nanocomposites studied for improvement in fracture toughness values.
Sr.
Authors
Year
1
Wan et al.
2014
Reinforcement/(wt %)
GO (0.25 wt %)
Dispersion
method
Sn + BM
DGEBA-f-GO (0.25 wt %)
2
Sharmila et al.
2014
3
Zhang et al.
2014
4
Moghadam et al.
2014
5
Ma et al.
2014
6
Chandrasekaran et al.
2014
MERGO (0.25 wt %)
GnPs (0.5 wt %)
Wan et al.
2014
MS + USn
Zaman et al.
2014
Jiang et al.
2014
10
Shokrieh et al.
2014
Ref.
K1C drops after 0.25 wt %
of reinforcement
[63]
K1C drops after 0.25 wt %
of reinforcement
[64]
Trend still increasing
fGnPs (0.3 wt %)
50.5
K1C drops after 0.3 wt % of
reinforcement
UG (0.5 wt %)
55
GO (0.5 wt %)
3RM
57
G-NH2 (0.5 wt %)
86
G-Si (0.5 wt %)
86
m-GnP (1 wt %)
[66]
K1C drops after 1 wt % of
reinforcement of m-GnP
[59]
131
44.5
Trend still increasing
3RM
49
K1C drops after 1 wt %
MWCNTs (0.5 wt %)
12.7
Trend still increasing
GO (0.1 wt %)
24
K1C improves with silane
functionalization
GNP (1 wt %)
Sn + BM
m-clay (2.5 wt %)
39
MS
SATPGO (0.5 wt %)
GPLs (0.5 wt %)
GNSs (0.5 wt %)
USn
Sn
[65]
K1C drops after 0.5 wt % of
reinforcement
MS + Sn
m-GP (4 wt %)
9
63
Remarks
27.6
Sn
Silane-f-GO (0.1 wt %)
8
25.6
40.7
TRGO (0.5 wt %)
7
% Increase in
K1C (MPa¨m1/2 )
[67]
[68]
38
K1C drops after 2.5 wt %
m-clay
103
Trend still increasing
92.8
K1C drops after 0.5 wt % of
reinforcement
[70]
K1C drops after 0.5 wt % of
reinforcement
[71]
39
16
[69]
Polymers 2016, 8, 281
5 of 37
Table 1. Cont.
Sr.
Authors
Year
11
Jia et al.
2014
12
Tang et al.
2013
Reinforcement/(wt %)
Dispersion
method
Wang et al.
2013
Chandrasekaran et al.
2013
15
Li et al.
2013
2013
2013
Liu et al.
2013
GO
1.72 µm (0.5 wt %)
20
Alishahi et al.
2013
2013
43
Dispersion and K1C improved
with three roll milling
[73]
25
Trend still increasing
43
K1C drops after 0.2 wt % of reinforcement
No effect
Fracture toughness improvement is higher by
CNF and GO (high aspect ratio) compared with
that by spherical ND
12
USn
GNPs* (0.5 wt %)
APTS-GO (0.5 wt %)
CNF (0.5 wt %)
ATS (1 wt %)
p-CNFs (0.4 wt %)
61
75
3RM
USn
USn
4.3
Sn
Sn
31
Trend remains same after 1 wt % of reinforcement
58.6
K1C drops after 0.1 wt % of reinforcement
86.2
The maximum improvement is achieved with
functionalization
41
Trend still increasing
K1C drops after 0.1 wt %
19
Trend still increasing after 0.2 wt %
ATP (1 wt %) + GO (0.2 wt %)
27
K1C drops with the further increase in ATP of
reinforcement
ND (0.5 wt %)
´26.9
CNF (0.5 wt %)
[75]
[76]
[77]
80
14
GO (0.2 wt %)
[74]
39.1
ATP (1 wt %)
Wang et al.
[57]
52
m-CNFs (0.4 wt %)
19
K1C drops after 0.5 wt % of reinforcement
Sn + BM
ATGO (1 wt %)
18
[72]
Highly dispersed RGO (0.2 wt %)
GO (0.1 wt %)
Jiang et al.
Trend still increasing
24
GO (0.5 wt %)
17
[58]
70
Sn
ND (0.5 wt %)
Shadlou et al.
K1C did not change much between 0.1 to 0.5 wt %
None
GPTS-GO (0.2 wt %)
16
Ref.
GF (0.1 wt %) (resin infiltration)
0.70 µm (0.1 wt %)
14
Remarks
Poorly dispersed RGO (0.2 wt %)
10.79 µm (0.5wt %)
13
% Increase in
K1C (MPa¨m1/2 )
Sn
Sn
19
GO (0.5 wt %)
23
CNT (0.5 wt %)
23.8
Trend still increasing
[78]
[79]
Polymers 2016, 8, 281
6 of 37
Table 1. Cont.
Sr.
Authors
Year
21
Ma et al.
2013
Reinforcement/(wt %)
U-GnP (0.5 wt %)
Dispersion
method
MgSr + USn
m-GnP (0.5 wt %)
22
Feng et al.
2013
Graphene (0.5 wt %)
24
25
Chatterjee et al.
Chatterjee et al.
Zaman et al.
2012
2012
2011
GnPs (25 µm, 2 wt %)
Sn
Rana et al.
2011
27
Bortz et al.
2011
3RM
Zhang et al.
2010
29
Fang et al.
2010
30
Jana et al.
2009
Rafiee et al.
2009
[80]
K1C decreases after 0.5 wt % of reinforcement
[81]
Trend still increasing
[82]
66
K1C drops after 0.1 wt % of reinforcement
[83]
57
[84]
90
The surface modification significantly improved
the K1C
40
K1C is dependent upon mixing time
[85]
60
K1C drops after 0.5 wt % of reinforcement
[86]
Trend still increasing
[87]
Better results with combination of MS and Sn
[88]
28
Trend still increasing
[89]
17
Graphene platelets have more influence on K1C
than CNTs
[90]
76
80
80
CNT:GnP = (9:1) (2 wt %)
76
EGNPs (0.1 wt %)
GP (2.5 wt %)
HPH + 3RM
Sn + MS
CNFs
Sn + MS
GO (0.5 wt %)
3RM
SCFs (15 wt %)
19.4
3RM
SCF (10 wt %)/CNF (0.75 wt %)
31
Trend still increasing
49
CNTs (2 wt %)
CNFs (0.5 wt %)
28
Ref.
60
m-GP (4 wt %)
26
Remarks
109
GnPs (5 µm, 2 wt %)
23
% Increase in
K1C (MPa¨m1/2 )
210
GNs
MS + Sn
GP with “puffed” structure (5 wt %)
Sn
SWNT (0.1 wt %)
MWNT (0.1 wt %)
125.8
Sn + MS
93.8
20
3RM: three roll milling; APTS-GO: amino-functionalized graphene oxide (GO); ATGO: 3-Aminopropyltriethoxysilane functionalized silica nanoparticles attached GO; ATP: attapulgite;
ATS: 3-amino functionalized silica nanoparticles; BM: ball milling; CNF: carbon nanofiber; CNT: carbon nanotube; DGEBA-f-GO: diglycidyl ether of bisphenol-A functionalized
GO; EGNP: amine functionalized expanded graphene nanoplatelets; fGnP: polybenzimidazole functionalized graphene platelets (GnPs); G-NH2: amino-functionalized GNPs;
G-Si: silane modified GNPs; GF: graphene foam; GN: amine functionalized graphene sheet; GnP: graphene platelet; GNP*: graphite nanoplatelet; GNS: graphene nanosheet; GO:
graphite; GP: graphite particles; GPL: graphene nanoplatelets; GPTS-GO: epoxy functionalized GO; HPH: high pressure homogenizer; m-clay: surface modified nano clay; m-CNF:
triazole functionalized carbon nanofiber; m-GnP: surface modified GnP; m-GnP*: surfactant modified graphene platelet; m-GP: surface modified graphene platelets; MERGO:
microwave exfoliated reduced graphene oxide; MgSr: magnetic stirring; MS: mechanical stirring; MWCNT: multi-walled carbon nanotube; MWNT: multi-walled carbon nanotubes;
ND: nanodiamond; pCNF: pristine carbon nanofibers; RGO: thermally reduced graphene oxide; SATPGO: 3-aminopropyltriethoxysilane modified silica nanoparticles attached GO;
SCF: short carbon fibers; Silane-f-GO: silane functionalized GO; Sn: Sonication; SWNT: single-walled carbon nanotubes; U-GnP: unmodified graphene platelets; UG: unmodified
graphene nanoplatelets; USn: ultrasonication.
Polymers 2016,
2016, 8,
8, 281
281
Polymers
Polymers 2016, 8, 281
of 35
35
66 of
7 of 37
Due to
to the
the pronounced
pronounced effect
effect of
of defects
defects on
on nanocomposite
nanocomposite properties,
properties, it
it is
is important
important to
to
Due
understand
how
a
system
will
tolerate
external
loading
in
the
presence
of
a
flaw
under
operating
understand
how
a system will
external
loading in the
presenceitof
a flaw under
operating
Due to the
pronounced
effecttolerate
of defects
on nanocomposite
properties,
is important
to understand
conditions, and
and how
how aa system
system will
will resist
resist the
the propagation
propagation of
of cracks
cracks from
from these
these flaws.
flaws. Therefore,
Therefore, how
how
conditions,
how a system will tolerate external loading in the presence of a flaw under operating conditions, and
the material will
will behave in
in reality will
will only
only be
be determined
determined when
when the
the test
test specimen
specimen contains
contains possible
possible
the
howmaterial
a system willbehave
resist thereality
propagation
of cracks
from these flaws.
Therefore,
how the material
will
flaws,
such
as
a
notch.
To
deal
with
this
issue
in
a
pragmatic
way,
an
intentional
notch
is
produced
flaws,
as a notch.
To deal
with this issue
inthe
a pragmatic
way,contains
an intentional
notch
is produced
behavesuch
in reality
will only
be determined
when
test specimen
possible
flaws,
such as a
in the
the specimen,
specimen, and
and resistance
resistance to
to fracture
fracture is
is measured
measured and
and is
is termed
termed fracture
fracture toughness.
toughness. Different
Different
in
notch.
To deal with this
issue in a pragmatic
way, an intentional
notch is produced
in the specimen,
specimens are
are used
used for
for fracture
fracture toughness,
toughness, such as
as notched
notched tension,
tension, three-point bending,
bending, and
specimens
and resistance
to fracture
is measured and is such
termed fracture
toughness.three-point
Different specimensand
are
compact
tension
specimen,
as
shown
in
Figure
1.
The
toughness
is
usually
measured
in
three
different
compact
as shown
Figure 1.tension,
The toughness
is usually
measured
in three different
used for tension
fracturespecimen,
toughness,
such asinnotched
three-point
bending,
and compact
tension
modes namely
namely (1)
(1) Mode-I (tensile
(tensile mode); (2)
(2) Mode-II (shearing
(shearing mode);
mode); and
and (3)
(3) Mode-III
Mode-III (tearing
(tearing
modes
specimen,
as shownMode-I
in Figure 1. Themode);
toughnessMode-II
is usually measured
in three different
modes namely
mode),
as
shown
in
Figure
2.
Most
of
the
literature
on
epoxy
nanocomposites
reported
Mode-I
mode),
as (tensile
shown in
Figure
Most of
the literature
nanocomposites
reported
Mode-I
(1)
Mode-I
mode);
(2) 2.
Mode-II
(shearing
mode); on
andepoxy
(3) Mode-III
(tearing mode),
as shown
in
fracture
toughness.
Mode-I
is
preferred
in
contrast
to
Mode-II,
because
shear
yielding
is
the
dominant
fracture
is preferred
contrast to Mode-II,
because
shear
yielding
is the dominant
Figure 2.toughness.
Most of theMode-I
literature
on epoxyinnanocomposites
reported
Mode-I
fracture
toughness.
Mode-I
mechanism of
of failure
failure that is
is acting
acting under
under Mode-II, delivering
delivering higher values
values than
than in
in Mode-I.
Mode-I. Modemechanism
is preferred in
contrastthat
to Mode-II,
because Mode-II,
shear yielding is the higher
dominant mechanism
of failureModethat is
III
is
never
practiced.
III
is never
practiced.
acting
under
Mode-II, delivering higher values than in Mode-I. Mode-III is never practiced.
Figure 1.
(b–d) compact
Various fracture
toughness test
specimen geometries:
geometries: (a)
(a) notched
Figure
1. Various
fracture toughness
toughness
test specimen
specimen
geometries:
notched tensile;
tensile; (b–d)
compact
tension;
(e)
compact
bend;
and
(f)
single-edge
notched
three-point
bend
specimens.
The
arrows
(e)
compact
bend;
and
(f)
single-edge
notched
three-point
bend
specimens.
The indicate
arrows
tension; (e) compact bend; and (f) single-edge notched three-point bend specimens. The
arrows
the
axis
of
loading.
indicate
the
axis
of
loading.
indicate the axis of loading.
Figure 2.
2. Various
Various
fracture modes:
modes: (a)
(a) mode-I,
mode-I, (b)
(b) mode-II,
mode-II, and
and (c)
(c) mode-III.
mode-III.
Various fracture
Figure
Some of the
the fracture toughness
toughness tests include
include double torsion,
torsion, indentation, double
double cantilever tests,
tests,
Some
Some of
of the fracture
fracture toughness tests
tests include double
double torsion, indentation,
indentation, double cantilever
cantilever tests,
and Chevron
Chevron notch
notch method.
method. Chevron
Chevron notch
notch method
method is popular,
popular, as
as it uses
uses aa relatively
relatively small
small amount
amount
and
and Chevron
notch method.
Chevron notch
method isispopular,
as it it
uses a relatively
small amount
of
of
material
and
no
material
constants
are
needed
for
the
calculations.
The
technique
is
also
suitable
of material and no material constants are needed for the calculations. The technique is also suitable
Polymers 2016, 8, 281
8 of 37
material and no material constants are needed for the calculations. The technique is also suitable for
high-temperature testing, as flaw healing is not a concern. However, it requires a complex specimen
shape that incurs an extra machining cost. The most commonly used specimen is a single-edge notched
beam subjected to three or four-point bending. Unfortunately, it has been reported that the results of
this test are very sensitive to the notch width and depth. Therefore, a pre-notched or molded beam is
preferred. As polymers and polymer nanocomposites can be molded into a desired shape, a specific
kind of notch can be replicated in multiple specimens. Due to the reproducibility of notch dimensions,
the single-edge notched beam test can give reproducible values of fracture toughness in polymers and
polymer nanocomposites. These are the reasons that most of the literature published on polymers
and polymer nanocomposites used single-edge notch beams (subjected to three-point bend loading)
to determine fracture toughness values (K1C ). Impact loading methods, such as Charpy and Izod
impact tests, are also used to determine impact fracture toughness. Fracture toughness values obtained
through different techniques cannot be directly compared [91].
Fracture can be defined as the mechanical separation of a solid owing to the application of stress.
Ductile and brittle are the two broad modes of fracture, and fracture toughness is related to the
amount of energy required to create fracture surfaces. In ideally-brittle materials (such as glass), the
energy required for fracture is simply the intrinsic surface energy of the materials, as demonstrated
by Griffith [92]. For structural alloys at room temperature, considerably more energy is required for
fracture, because plastic deformation accompanies the fracture process. In polymer nanocomposites,
the fracture path becomes more tortuous as cracks detour around strong reinforcement. This increase in
crack tortuosity provides additional work to fracture and, therefore, an increase in fracture toughness.
In polymers, the fracture process is usually dominated by crazing or the nucleation of small cracks and
their subsequent growth [93].
Toughness is defined as the ability of a material to absorb energy before fracture takes place. It
is usually characterized by the area under a stress–strain curve for a smooth (un-notched) tension
specimen loaded slowly to fracture. The term fracture toughness is usually associated with the fracture
mechanics methods that deal with the effect of defects on the load-bearing capacity of structural
components. The fracture toughness of materials is of great significance in engineering design because
of the high probability of flaws being present. Defined another way, it is the critical stress intensity at
which final fracture occurs. The plane strain fracture toughness (critical stress intensity factor, K1C )
can be calculated for a single-edge notched three-point bending specimen using Equation (1), where
Pmax is the maximum load of the load–displacement curve (N), f (a/w) is a constant related to the
geometry of the sample and is calculated using Equation (2), B is sample thickness (mm), W is sample
width (mm), and a is crack length (a should be kept between 0.45 W and 0.55 W, according to ASTM
D5045) [72]. The critical strain energy release rate (G1C ) can be calculated using Equation (3), where
E is the Young’s modulus obtained from the tensile tests (MPa), and ν is the Poisson’s ratio of the
polymer. The geometric function f(a/W) strongly depends on the a/W ratio [94].
The fracture toughness is dependent on many factors, such as type of loading and environment
in which the system will be loaded [95]. However, the key defining factor is the microstructure as
summed up in Figure 3 [96]. The properties of nanocomposites are also significantly dependent on filler
shape and size [51]. The graphene size, shape, and topography can be controlled simultaneously [97].
K1C “
”
“
!
p2` Wa q
a
Pmax f p W
q
f W
a ´13.32 a 2 `14.72 a 3 ´5.6
0.0866`4.64p W
q
pW q
pW q
p
p
a
4
W
q
)ı
(2)
a 3{2
1´ W
q
`
G1c
(1)
BW 1{2
`a˘
K 2 1 ´ ν2
“ 1c
E
˘
(3)
Polymers 2016, 8, 281
Polymers 2016, 8, 281
9 of 37
8 of 35
Figure 3. Various aspects of microstructure.
Figure 3. Various aspects of microstructure.
5. Structure and Fracture Toughness
5. Structure and Fracture Toughness
Graphene has a honeycomb lattice having sp22 bonding, which is much stronger than the sp33
Graphene has a honeycomb lattice having sp bonding, which is much stronger than the sp
bonding found in diamond [98]. There is sp2 2orbital hybridization between Px and Py that forms a σbonding found in diamond [98]. There is sp orbital hybridization between P and P that forms a
bond [52]. The orbital Pz forms a π-bond with half-filled band that allows freex motiony of electrons.
σ-bond [52]. The orbital Pz forms a π-bond with half-filled band that allows free motion of electrons.
When bombarded with pure
carbon atoms, hydrocarbons, or other carbon-containing molecules, the
When bombarded with pure carbon atoms, hydrocarbons, or other carbon-containing molecules, the
graphene directs the carbon atoms into vacant seats, thereby self-repairing the holes in the graphene
graphene directs the carbon atoms into vacant seats, thereby self-repairing the holes in the graphene
sheet. Through their crack deflection modeling, Faber and Evans showed that maximum
sheet. Through their crack deflection modeling, Faber and Evans showed that maximum improvement
improvement in fracture toughness, among all other nano-reinforcements, can be obtained using
graphene—mainly because of its better capability of deflecting the propagating cracks [99,100].
Polymers 2016, 8, 281
10 of 37
in fracture toughness, among all other nano-reinforcements, can be obtained using graphene—mainly
because of its better capability of deflecting the propagating cracks [99,100].
As graphene is a 2D structure, each carbon atom can undergo chemical reaction from the sides,
resulting in high chemical reactivity. The carbon atoms on the edge of graphene sheet have three
incomplete bonds (in single layer graphene) that impart especially high chemical reactivity to edge
carbon atoms. In addition, defects within a graphene sheet are high energy sites and preferable sites
for chemical reactants. All these factors make graphene a very highly chemical reactive entity. The
graphene oxide can be reduced by using Al particles and potassium hydroxide [101]. The graphene
structure can be studied using Transmission Electron Microscopy (TEM) and other high-resolution
tools. Wrinkles were observed in graphene flat sheet, which were due to the instability of the 2D lattice
structure [72,102].
Wrinkling is a large and out-of-plane deflection caused by compression (in-plane) or shear.
Wrinkling is usually found in thin and flexible materials, such as cloth fabric [103]. Graphene
nanosheets (GNSs) were also found to undergo a wrinkling phenomenon [104]. When wrinkling
takes place, strain energy is stored within GNSs which is not sufficient to allow the GNSs to regain
their shape. Wrinkling can be found on GNSs as well as on exfoliated graphite. The wrinkles in
GNSs are sundering apart at different locations while getting closer at other regions. As GNSs do not
store sufficient elastic strain energy, wrinkling is an irreversible phenomenon, but can be altered by
external agency [105]. The surface roughness varies depending on graphene sheets, owing to their
dissimilar topographical features, such as wrinkles’ size and shape. Therefore, the ability of sheets
to mechanically interlock with other sheets and polymer chains is dissimilar. Wang et al. showed
that a wrinkle’s wavelength and amplitude are directly proportional to sheet size (length, width, and
thickness), as is clear from Equations (4) and (5), where λ is wrinkle wavelength, ν is Poisson’s ratio, L
is graphene sheet size, t is thickness of graphene sheet, ε is edge contraction on a suspended graphene
sheet, and A is wrinkle amplitude [57].
Palmeri et al. showed that the graphene sheets have a coiled structure that helps them to store a
sufficient amount of energy [106]. The individual sheet and chunk of sheets together are subjected to
plastic deformation at the application of external load. The applied energy is utilized in undertaking
plastic work that enhances the material’s ability to absorb more energy. It is believed that large
graphene sheets have large size wrinkles [107]. These wrinkles twist, bend, and fold the graphene
sheets. The wrinkles and other induced defects remain intact while curing of polymer matrix. This
reduces the geometric continuity and regularity of graphene and lowers load transfer efficiency, and
can cause severe localized stress concentration.
λ4 «
4π2 νL2 t2
˘
`
3 1 ´ ν2 ε
(4)
A4 «
16νL2 t2 ε
`
˘
3π2 1 ´ ν2
(5)
6. Surface Area and Fracture Toughness
K1C strongly depends upon the surface area of the reinforcement, as it influences the
matrix–reinforcement interfacial interactions. When the reinforcement has a large surface area, the
interfacial area increases, which increases the number of routes for the transport of load from matrix to
reinforcement [87]. On the contrary, when agglomeration takes place, not only the agglomerates act as
stress raisers, but the net surface area is also decreased, which further drops the fracture toughness
and other mechanical properties of nanocomposites [108]. One reason that graphene supersedes other
reinforcements is its high surface area [109]. The surface area of graphene is even higher than that of
CNTs [110]. To make a comparison, the surface areas of short carbon fiber and graphene are calculated.
The surface area of carbon fiber is calculated using the formula for a solid cylinder, while the surface
Polymers 2016, 8, 281
11 of 37
area of graphene is calculated using the formula for a rectangular sheet. The thickness of graphene is
considered variable, so the same relation can be used for multiple layers of graphene sheets stacked
together in the form of graphene nanosheets. The length of short carbon fiber is taken to be 1 µm and
the diameter 0.1 µm. The dimensions of graphene are ` ˆ w ˆ t = 1 µm ˆ 0.1 µm ˆ 10 nm. The density
of both short carbon fiber and graphene is taken to be 2.26 to make comparison based on dimensions
only. The surface area of 1 g of carbon fibers is 19 m2 and that of graphene is 98 m2 . It can be observed
that although the lengths of both reinforcements are the same and the width of graphene is equal to
the diameter of a short carbon fiber, there is a large difference in surface areas when the thickness
of graphene is kept 10 nm. This difference will further increase if graphene dimensions are reduced.
The specific surface area of graphene is as high as 2600 m2 /g [111,112]. It shows that graphene,
having a much larger surface area, can significantly improve the fracture toughness of the epoxy
nanocomposites [113,114]. There is also improved thermal conduction among graphene–graphene
links that significantly improves the overall thermal conductivity of the nanocomposites [115,116].
The electrical conductivity also increases with graphene as graphene sheets form links and provide a
passageway for electrical conduction [117].
Zhao and Hoa used a theoretical computer simulation approach to study the improvement in
toughness when epoxy is reinforced with 2D nano-reinforcements of different particle size [118,119].
The simulation results showed that there is a direct relation between particle size and stress
concentration factor up to 1 µm, after which point the stress concentration factor was impervious to any
further size increase. However, Chatterjee et al. [82] showed that fracture toughness was improved by
increasing the graphene size, which is in negation with simulation results by Zhao and Hoa [120,121].
The relationship between graphene size and stress concentration factor can be correlated with the
facile analogy of substitutional solid solution. The extent of strain field produced by a foreign atom
depends upon the difference in atomic sizes of the foreign and parent atoms. When there is a large
difference between foreign and parent atoms, a large strain field around the atom is generated. On the
contrary, when the difference in atomic sizes of parent and foreign atoms is small, the strain field is
limited. As both atomic and GNPs sizes are in the nano-meter range, the analogy can arguably be
applied to an epoxy–graphene system where large sheet size will cause higher stress concentration
factor than that produced by small sheet size. Therefore, graphene with smaller sheet size can be more
efficient in improving the fracture toughness than the larger graphene sheets.
The increase in the fracture toughness of epoxy was found to be strongly dependent upon the
graphene sheet size [57]. For the nanocomposites, an inverse relation was found between sheet size
and fracture toughness in most cases. The increase in fracture toughness with a decrease in sheet size
can be explained on the basis of stress concentration factor, as discussed above. Although graphene
acts as reinforcement, however, it has associated stress and strain fields which arise from the distortion
of the structure of polymer matrix. When sheet size, weight fraction, or both are increased beyond a
certain value, the stress concentration factor dominates the reinforcing character. As a result, fracture
toughness and other mechanical properties—such as tensile and flexural strength and stiffness—start
decreasing, which is in accordance with Zhao and Hoa’s simulation results [118].
Wang et al. used Graphene Oxide (GO) of three different sizes, namely GO-1, GO-2, GO-3,
having average diameters 10.79, 1.72, and 0.70 µm, respectively, to produce nanocomposites using
an epoxy matrix [57]. They observed that fracture toughness was strongly dependent on GO sheet
size. The maximum increase in fracture toughness was achieved with the smallest GO sheet size.
The K1C values dropped when weight fraction was increased beyond 0.1 wt %. This decrease in K1C
with increasing weight fraction can be correlated with crack generation and dispersion state.
7. Weight Fraction and Fracture Toughness
The K1C first increases with GO and then starts decreasing in all three of the cases. The increase
in K1C is due to the reinforcing effect of GO, while the drop in K1C is due to crack generation and
agglomeration. The addition of a high GO weight fraction generates cracks that reduce the fracture
Polymers 2016, 8, 281
12 of 37
toughness of the nanocomposite [57]. The other reason for such behavior is due to the high probability
of agglomeration at higher weight fractions due to Van der Waals forces [57].
The weight fractions of reinforcements at which maximum K1C was achieved for different
epoxy–graphene
stated
Polymers 2016, 8, 281 nanocomposites are shown in Figure 4. All the published research articles 11
of 35
that the maximum K1C values were achieved at or below 1 wt % of graphene, and K1C dropped when
the weight fraction of graphene was
was raised
raised beyond
beyond 11 wt
wt %.
%. The
The decrease
decrease in
in KK1C
1C with a higher weight
fraction of graphene can be correlated with the dispersion
dispersion state
state of
of graphene.
graphene. As graphene weight
dispersion
state
becomes
inferior.
TheThe
maximum
increase
in K1C
fraction increases
increasesbeyond
beyond11wt
wt%,%,the
the
dispersion
state
becomes
inferior.
maximum
increase
in
was
131%,
which
is achieved
at 1 wt
graphene
[59]. However,
the dispersion
mode mode
adopted
is worth
K1C was
131%,
which
is achieved
at 1%wt
% graphene
[59]. However,
the dispersion
adopted
is
discussing.
The graphene
was dispersed
using ausing
combination
of sonication
and mechanical
stirring.
worth
discussing.
The graphene
was dispersed
a combination
of sonication
and mechanical
This
combination
provides provides
an efficient
of dispersing
the graphene
epoxy. into
In addition
to
stirring.
This combination
anmeans
efficient
means of dispersing
theinto
graphene
epoxy. In
that, sonication
exfoliation,
length shortening
of shortening
graphene sheets.
These aspects
addition
to that,causes
sonication
causesdelayering,
exfoliation,and
delayering,
and length
of graphene
sheets.
help alleviate
concentration
factor and cracks
associated
with
large graphene
sheets.
These
These
aspects the
helpstress
alleviate
the stress concentration
factor
and cracks
associated
with large
graphene
factors result
K1C improvement
to 131%, which
is the
maximum
among
the improvements
in
sheets.
These in
factors
result in K1C up
improvement
up to
131%,
which is
the maximum
among the
K
values
reported
in
epoxy–graphene
nanocomposites.
improvements
in
K
1C
values
reported
in
epoxy–graphene
nanocomposites.
1C
140
Increase in K1C (% )
120
100
80
60
40
20
0
0.1
0.2
0.25
0.3
0.4
Reinforcement (Wt%)
0.5
1
Figure
4. The
The weight
weight fractions
fractions of
of reinforcements
reinforcements at
at which
which maximum
maximum K
K1C
1C was
different
Figure 4.
was achieved
achieved in
in different
epoxy/graphene
(See
references
in
epoxy/graphene nanocomposites
nanocompositesand
andcorresponding
correspondingimprovement
improvement(%)
(%)in inK1CK1C
(See
references
Table
1).
in Table 1).
It can be observed from Figure 4 that there is no fixed value of GNPs wt % at which a maximum
It can be observed from Figure 4 that there is no fixed value of GNPs wt % at which a maximum
increase in K1C is achieved. In addition, the increase in K1C at fixed GNP wt % is not the same. For
increase in K1C is achieved. In addition, the increase in K1C at fixed GNP wt % is not the same.
example, at 0.5 wt %, the % increase in K1C is reported to be up to 45% by Chandrasekaran et al. [67], and
For example, at 0.5 wt %, the % increase in K1C is reported to be up to 45% by Chandrasekaran et al. [67],
about 110% by Ma et al. [80]. Therefore, it can be concluded that the wt % of GNPs is not the sole
and about 110% by Ma et al. [80]. Therefore, it can be concluded that the wt % of GNPs is not the
factor defining the influence of GNPs on the mechanical properties of nanocomposites. There are
sole factor defining the influence of GNPs on the mechanical properties of nanocomposites. There are
other influential factors as well, such as dispersion method, use of dispersant, and functionalization.
other influential factors as well, such as dispersion method, use of dispersant, and functionalization.
In addition, the use of organic solvent is another important parameter in defining the improvement
In addition, the use of organic solvent is another important parameter in defining the improvement
in mechanical properties. It was observed that a lower improvement in K1C was observed when
in mechanical properties. It was observed that a lower improvement in K1C was observed when
dispersion was carried out with only sonication, and a higher improvement in K1C was observed
dispersion was carried out with only sonication, and a higher improvement in K1C was observed when
when sonication was assisted with a secondary dispersion method, especially mechanical stirring.
sonication was assisted with a secondary dispersion method, especially mechanical stirring.
8. Dispersion State and Fracture Toughness
The end product of most of the graphene synthesis methods is agglomerated graphene [33]. In
addition, graphene tends to agglomerate due to weak intermolecular Van der Waals forces [113].
Therefore, dispersing graphene in epoxy matrix is always a challenge. The relationship between
dispersion state and the nature of crack advancement is shown schematically in Figure 5. The
advancing cracks can be best barricaded by uniformly dispersed graphene. Tang et al. produced
Polymers 2016, 8, 281
13 of 37
8. Dispersion State and Fracture Toughness
The end product of most of the graphene synthesis methods is agglomerated graphene [33].
In addition, graphene tends to agglomerate due to weak intermolecular Van der Waals forces [113].
Therefore, dispersing graphene in epoxy matrix is always a challenge. The relationship between
dispersion state and the nature of crack advancement is shown schematically in Figure 5.
The advancing cracks can be best barricaded by uniformly dispersed graphene. Tang et al. produced
highly
dispersed
Polymers
2016, 8, and
281 poorly dispersed RGO-epoxy nanocomposites using solution casting technique.
12 of 35
The high dispersion of RGO in epoxy was achieved using a ball milling process [72]. The RGO
dispersed
in epoxy
using
sonicationprocess
processand
and not
not subjected
subjected totoball
was
termed
poorly
dispersed
in epoxy
using
sonication
ballmilling
milling
was
termed
poorly
dispersed. They studied the influence of graphene dispersion on the mechanical properties of the
dispersed. They studied the influence of graphene dispersion on the mechanical properties of the
produced nanocomposite. The highly dispersed RGO-epoxy showed a 52% improvement in K1C,
produced nanocomposite. The highly dispersed RGO-epoxy showed a 52% improvement in K1C ,
while the poorly dispersed RGO-epoxy showed only a 24% improvement in K1C. It shows that better
whiledispersion
the poorly of
dispersed
RGO-epoxy showed only a 24% improvement in K1C . It shows
that better
graphene can significantly improve the fracture toughness
of epoxy
dispersion
of
graphene
can
significantly
improve
the
fracture
toughness
of
epoxy
nanocomposites
[72].
nanocomposites [72].
Figure
5. Influence
graphenedispersion
dispersion on
on crack
crack propagation
propagation method;
poorly
dispersed
Figure
5. Influence
of of
graphene
method;(a)(a)
poorly
dispersed
graphene;
Ideally
uniformly dispersed
dispersed graphene.
The The
arrows
indicate
the paththe
followed
by cracks by
graphene;
(b) (b)
Ideally
uniformly
graphene.
arrows
indicate
path followed
thethe
graphene
sheets.
cracksthrough
through
graphene
sheets.
Several dispersion modes to disperse reinforcement into epoxy matrix were successfully
adopted (see references in Table 1). The maximum % increase in K1C as a function of dispersion mode
is shown in Figure 6. In most of these articles, sonication is the main mode of dispersing reinforcement
in epoxy matrix. It can be observed that when sonication is assisted by a supplementary dispersion
technique (such as mechanical stirring and magnetic stirring), the K1C values were significantly
Polymers 2016, 8, 281
14 of 37
Several dispersion modes to disperse reinforcement into epoxy matrix were successfully adopted
(see references in Table 1). The maximum % increase in K1C as a function of dispersion mode is shown
in Figure 6. In most of these articles, sonication is the main mode of dispersing reinforcement in epoxy
matrix. It can be observed that when sonication is assisted by a supplementary dispersion technique
Polymers 2016, 8, 281
13 of 35
(such as mechanical stirring and magnetic stirring), the K1C values were significantly increased.
The maximum improvement of 131% in K1C was achieved when a combination of sonication and
sonication and mechanical stirring was employed [59]. The second highest improvement in K1C was
mechanical stirring was employed [59]. The second highest improvement in K1C was achieved with a
achieved with a combination of sonication and magnetic stirring, an increase in K1C of 109% [80]. The
combination of sonication and magnetic stirring, an increase in K1C of 109% [80]. The minimum values
minimum values in K1C improvements are achieved when sonication is coupled with ball milling
in K1C improvements are achieved when sonication is coupled with ball milling [60,64,100]. Since both
[60,64,100]. Since both the sonication and ball milling processes reduce the sheet size and produce
the sonication and ball milling processes reduce the sheet size and produce surface defects [120–134],
surface defects [120–134], we believe that the surface defects significantly increased and sheet size
we believe that the surface defects significantly increased and sheet size was reduced below the
was reduced below the threshold value, and therefore a greater improvement in K1C was not
threshold value, and therefore a greater improvement in K1C was not achieved. Although three roll
achieved. Although three roll milling (3RM, calendering process) is an efficient way of dispersing the
milling (3RM, calendering process) is an efficient way of dispersing the reinforcement into the polymer
reinforcement into the polymer matrix due to high shear forces, the maximum improvement in K1C
matrix due to high shear forces, the maximum improvement in K1C using three roll mill was reported
using three roll mill was reported as 86% [77], which is far below that achieved with a combination
as 86% [77], which is far below that achieved with a combination of sonication and mechanical stirring
of sonication and mechanical stirring (131% [59]).
(131% [59]).
Increase in K1C (%)
150
100
50
0
Mode of dispersion
Figure 6.
improvement
in Kin1CK
as1Ca function
of dispersion
mode. mode.
(See references
in Table
Figure
6. The
Themaximum
maximum
improvement
as a function
of dispersion
(See references
1). Table 1).
in
9. Functionalization
9.
Functionalizationand
andFracture
FractureToughness
Toughness
Achieving
toughness of
polymers by
by using
using graphene
graphene
Achieving maximum
maximum improvement
improvement in
in fracture
fracture toughness
of polymers
depends
on
the
ability
to
optimize
the
dispersibility
of
graphene
and
the
interfacial
interactions
with
depends on the ability to optimize the dispersibility of graphene and the interfacial interactions
the
epoxy
matrix.
As
described
previously,
graphene
tends
to
agglomerate
due
to
the
weak
Van
der
with the epoxy matrix. As described previously, graphene tends to agglomerate due to the weak
Waals
interactions,
and its smoother
surface texture
interfacial
interactions.
To tackle
Van
der
Waals interactions,
and its smoother
surfaceinhibits
texturestrong
inhibits
strong interfacial
interactions.
the
limited
dispersibility
and
interfacial
bonding
of
graphene,
surface
modifications
are
carried
To tackle the limited dispersibility and interfacial bonding of graphene, surface modifications out
are
[135–139].
In
fact,
the
introduction
of
functional
groups
on
the
graphene
surface
can
induce
novel
carried out [135–139]. In fact, the introduction of functional groups on the graphene surface can
properties
[140–144].
Various
methods
to modify
the graphene
surface
been employed,
andbeen
can
induce
novel
properties
[140–144].
Various
methods
to modify
the have
graphene
surface have
be
categorized
into
two
main
groups,
namely:
(1)
chemical
functionalization;
and
(2)
physical
employed, and can be categorized into two main groups, namely: (1) chemical functionalization; and
functionalization.
(2)
physical functionalization.
In
chemical functionalization,
In chemical
functionalization, chemical
chemical entities
entities are
are typically
typically attached
attached covalently.
covalently. For
For example,
example,
in
defect
functionalization,
functional
groups
are
attached
at
the
defect
sites
of
graphene,
in defect functionalization, functional groups are attached at the defect sites of graphene, such as
such as –COOH
(carboxylic
–OH (hydroxyl)
groups.can
Defects
be any departure
from
–COOH
(carboxylic
acid) andacid)
–OHand
(hydroxyl)
groups. Defects
be anycan
departure
from regularity,
regularity,
including
pentagons
and
heptagons
in
the
hexagonal
structure
of
graphene.
Defects
may
including pentagons and heptagons in the hexagonal structure of graphene. Defects may also
be
also
be
produced
by
reaction
with
strong
acids
such
as
HNO
3, H2SO4, or their mixture, or strong
produced by reaction with strong acids such as HNO3 , H2 SO4 , or their mixture, or strong oxidants
oxidants including
ozone,
and reactive
plasmaThe
[145].
The functional
attached
at the
including
KMnO4 , KMnO
ozone,4,and
reactive
plasma [145].
functional
groups groups
attached
at the defect
defect sites of graphene can undergo further chemical reactions, including but not limited to
silanation, thiolation, and esterification [146]. Unlike chemical functionalization, physical
functionalization has non-covalent functionalization, where the supermolecular complexes of
graphene are formed as a result of the wrapping of graphene by surrounding polymers [33].
Surfactants lower the surface tension of graphene, thereby diminishing the driving force for the
Polymers 2016, 8, 281
15 of 37
sites of graphene can undergo further chemical reactions, including but not limited to silanation,
thiolation, and esterification [146]. Unlike chemical functionalization, physical functionalization has
non-covalent functionalization, where the supermolecular complexes of graphene are formed as a
result of the wrapping of graphene by surrounding polymers [33]. Surfactants lower the surface
Polymers
8, 281
14 of
35
tension2016,
of graphene,
thereby diminishing the driving force for the formation of aggregates.
The
graphene dispersion can be enhanced by non-ionic surfactants in case of water-soluble polymers [33].
The different functionalization methods adopted to study their influence on K1C values with
The different functionalization methods adopted to study their influence on K1C values with
corresponding improvements (%) in K1C values are shown in Figure 7. The minimum improvement
corresponding improvements (%) in K1C values are shown in Figure 7. The minimum improvement was
was achieved for amino-functionalized graphene oxide (APTS-GO) [74], while the maximum
achieved for amino-functionalized graphene oxide (APTS-GO) [74], while the maximum improvement
improvement was recorded for surfactant-modified graphene nanoplatelets [59]. This could be
was recorded for surfactant-modified graphene nanoplatelets [59]. This could be attributed to the
attributed to the improvement in the dispersion state of graphene in the epoxy matrix when
improvement in the dispersion state of graphene in the epoxy matrix when surfactants were used, in
surfactants were used, in addition to improving interactions without causing a reduction in graphene
addition to improving interactions without causing a reduction in graphene sheet size or imparting
sheet size or imparting surface defects on graphene sheets.
surface defects on graphene sheets.
140
Increase in K1C (%)
120
100
80
60
40
20
0
Type of functionalization
Figure7.7.The
Themaximum
maximumimprovement
improvementin
inKK1C1Casasa afunction
functionofoffunctionalization
functionalizationmethod.
method.(See
(Seereferences
references
Figure
in
Table
1).
in Table 1).
10.
10.Crosslink
CrosslinkDensity
Densityand
andFracture
FractureToughness
Toughness
In
thermosettingmaterials,
materials,
such
as epoxy,
high crosslink
is for
desirable
for the
In thermosetting
such
as epoxy,
high crosslink
density isdensity
desirable
the improvement
improvement
mechanical However,
properties.high
However,
highdensity
crosslink
density
has a detrimental
on
of mechanicalofproperties.
crosslink
has
a detrimental
effect oneffect
fracture
fracture
toughness
[57]. Therefore,
a crosslink
threshold
is required
to achieve
toughness
[57]. Therefore,
a crosslink
density density
threshold
is required
in orderintoorder
achieve
optimal
optimal
properties
During
the
of thermoset
while
phase transformation
properties
[147,148].[147,148].
During the
curing
ofcuring
thermoset
polymers,polymers,
while phase
transformation
takes place,
takes
place,
graphene
tend to in
agglomerate
in order
to reduce configurational
entropy [57].
graphene
sheets
tend tosheets
agglomerate
order to reduce
configurational
entropy [57]. Additionally,
the
Additionally,
the reduces
viscositywhen
initially
reduces when
the temperature
is increased
which
viscosity initially
the temperature
is increased
during curing,
whichduring
makescuring,
the movement
makes
the movement
the graphene
sheets relatively
easy, supporting
agglomeration.
Due to
of the graphene
sheetsof
relatively
easy, supporting
their agglomeration.
Duetheir
to the
wrinkle-like structure
the
wrinkle-like
structure
and
high
specific
surface
area
of
graphene,
strong
interfacial
interactions
and high specific surface area of graphene, strong interfacial interactions are possible with epoxy
are
possible
with
chains.
It curing
may also
affectbythe
overall the
curing
reaction
by changing
the
chains.
It may
alsoepoxy
affect the
overall
reaction
changing
maximum
exothermic
heat flow.
maximum
heat flow.
Molecular
dynamics
studies
conducted
by Smith
al. also
Molecular exothermic
dynamics studies
conducted
by Smith
et al. also
showed
that there
was a et
change
in showed
polymer
that
there
was acaused
changeby
ingeometric
polymer chain
mobility
caused
by geometric
constraints at
the surface of
chain
mobility
constraints
at the
surface
of nano-reinforcement
[149].
nano-reinforcement
[149]. the crosslink density of epoxy [65]. When graphene is dispersed in epoxy,
The graphene affects
The graphene
the crosslink
density of epoxy
[65]. When
in epoxy,
the polymer
chainsaffects
are restricted,
and crosslinking
is decreased.
Thegraphene
decrease is
indispersed
crosslinking
lowers
the polymer chains are restricted, and crosslinking is decreased. The decrease in crosslinking lowers
the heat release rate. It was reported that both graphene platelets (GnPs) and polybenzimidazole
functionalized GnPs (fGnPs) decreased the heat release rate of the curing reaction and increased the
curing temperature [65]. It can also be attributed to the dispersion state of the reinforcement.
Uniformly dispersed reinforcement will have a more pronounced effect on heat release rate and
curing temperature than poorly dispersed reinforcement. Therefore, fGnPs have a better dispersion
Polymers 2016, 8, 281
16 of 37
the heat release rate. It was reported that both graphene platelets (GnPs) and polybenzimidazole
functionalized GnPs (fGnPs) decreased the heat release rate of the curing reaction and increased
the curing temperature [65]. It can also be attributed to the dispersion state of the reinforcement.
Uniformly dispersed reinforcement will have a more pronounced effect on heat release rate and curing
temperature than poorly dispersed reinforcement. Therefore, fGnPs have a better dispersion state
than GnPs [65]. There are two opposite effects of filler in the matrix: (1) the fillers could restrict the
polymer chains, which should increase Tg ; (2) the reactive fillers could lower the crosslinking density
of epoxy, which should decrease Tg . An increase in Tg shows that interfacial interactions dominate the
crosslinking density effect [65].
11. Fracture Patterns
Monolithic epoxy exhibits a bamboo-like brittle fracture pattern [105]. However, with the
incorporation of graphene, the cracks are deflected, resulting in parabolic and non-linear fracture
patterns [105]. The change in graphene structure and shape upon the application of external stress also
affects the overall fracture pattern of the nanocomposite, due to changes in mechanical interlocking and
interfacial interactions [105]. It was recorded that bending behavior of GNSs when wrapping around
a corner resulted in the sliding of layers over one another, and was termed “sliding mode” [105].
In sliding mode, angular change (γ) was observed. This γ was produced when layers slid over
one another. If the state of stress is relatively high, the inner layers undergo splitting and buckling
that further results in kinking, by which the bending stress is alleviated [105]. GNSs size and edge
morphology control the type of fracture mode. In the case of smaller GNSs (smaller refers to volume
of individual GNSs), where the sliding surface is smaller, the resistance to sliding is lower, and hence
sliding mode will be preferred. On the contrary, if GNSs are of larger size and the sides are longer,
the resistance to sliding would be higher, and hence buckling mode will be preferred over sliding
mode [105]. The tearing step subdivides into multiple steps. Consequently, the initial crack branches
into multiple small cracks [105]. However, the extent of subdivision of the advancing cracks depends
on the dispersion state of the filler and interfacial interactions.
12. Other Mechanical Properties
The literature shows an absence of consensus on the role of graphene in improving other
mechanical properties of nanocomposites. Some authors reported significant improvement in the
mechanical properties of nanocomposites reinforced with GNPs [150–154]. On the other hand, there
was no significant effect due to the incorporation of GNPs into epoxy matrix [155–158], and even
worse, the mechanical properties deteriorated by the addition of GNPs [159–163]. In general, a major
portion of the literature has shown that GNPs can significantly improve the mechanical properties
of epoxy nanocomposites. The percent improvements in tensile strength and tensile modulus are
shown in Figure 8. The maximum improvement in tensile strength is as high as 108% [164] and
in the tensile modulus up to 103% [165]. GNPs were also found to improve flexural properties of
nanocomposites. Naebe et al. produced covalent functionalized epoxy–graphene nanocomposites,
and reported 18% and 23% increase in flexural strength and modulus, respectively [166]. Qi et al.
produced graphene oxide–epoxy nanocomposites and reported an increase of up to 53% in flexural
strength [167]. The impact strength and hardness were also significantly improved by graphene in
epoxy nanocomposites. For example, Ren et al. applied a combination of bath sonication, mechanical
mixing, and shear mixing to disperse GO in cyanate ester–epoxy and produced nanocomposites using
in situ polymerization [168]. They reported an increase of 31% in impact strength. Qi et al. produced
graphene oxide–epoxy nanocomposites and reported an increase in impact strength of up to 96% [169],
whereas Lu et al. produced GO–epoxy nanocomposites and reported an increase in impact strength
of up to 100% [170]. Shen et al. produced GNS–epoxy nanocomposites and reported an increase in
impact strength of up to 11% [171], and Bao et al. reported an increase in hardness of up to 35% [172].
Polymers 2016, 8, 281
17 of 37
The G1C also improved with the incorporation of graphene in epoxy nanocomposites. Meng et al.
produced epoxy–graphene nanocomposites and reported an increase in G1C of up to 597% [173].
13. Thermal Properties
Due to the superior thermal conductivity of graphene, graphene-based polymer nanocomposites
Polymers
8, 281 candidates for high-performance thermal interface materials [174]. The dissipation of
16 of 35
are 2016,
promising
heat from electronic devices may also be barricaded when the high thermal conductivity of graphene is
conductivity
of polymers
than CNTs
[175].higher
It has
been found
experimentally
that the Effective
efficiently utilized.
The graphene
has shown
efficiency
in increasing
the thermal conductivity
of
Thermal
Conductivity
(K
eff
)
of
graphene-based
polymer
nanocomposites
has
a
non-linear
polymers than CNTs [175]. It has been found experimentally that the Effective Thermal Conductivity
dependence
on graphene polymer
weight nanocomposites
fraction [176–178].
et al. dependence
proposed an
analyticalweight
model to
(Keff ) of graphene-based
has a Xie
non-linear
on graphene
fractionthe
[176–178].
Xie et al. proposed
an analytical model
determine
Keff of graphene-based
determine
Keff of graphene-based
nanocomposites
[179].toTheir
modelthe
proposed
very high thermal
nanocomposites
Their
model
thermal
values, resistance.
as the modelLin et
conductivity
values,[179].
as the
model
didproposed
not take very
into high
account
the conductivity
interfacial thermal
did
not
take
into
account
the
interfacial
thermal
resistance.
Lin
et
al.
developed
a
model
al. developed a model based on Maxwell–Garnett effective medium approximation based
theory to
on Maxwell–Garnett
effectiveconductivity
medium approximation
theory tonanocomposites
determine the effective
thermal
determine
the effective thermal
of graphene-based
[180,181].
conductivity of graphene-based nanocomposites [180,181]. They showed that the enhancement in
They showed that the enhancement in thermal conductivity is strongly influenced by the aspect ratio
thermal conductivity is strongly influenced by the aspect ratio and orientation of graphene.
and orientation of graphene.
120
Tensile
strength
% increase
100
80
60
40
20
0
Authors
Figure 8. The % increase in tensile properties of epoxy/graphene nanocomposites [164,165,182–191].
Figure 8. The % increase in tensile properties of epoxy/graphene nanocomposites [164,165,182–191].
n
4000
3000
2000
1000
0
BM
SM
M
M
S
% increase in thermal
conductivity
et used
al. used
a molecular
dynamicsapproach
approachto
toshow
show that
that the
is is of
Hu Hu
et al.
a molecular
dynamics
the agglomeration
agglomerationofofgraphene
graphene
of major concern in increasing the thermal conductivity of the system [192]. The variation in thermal
major
concern in increasing the thermal conductivity of the system [192]. The variation in thermal
conductivity with various forms of graphene and graphite nanocomposites is summarized in Table 2,
conductivity with various forms of graphene and graphite nanocomposites is summarized in Table
and the influence of dispersion mode on the improvement of thermal conductivity is shown in Figure 9.
2, and
the influence of dispersion mode on the improvement of thermal conductivity is shown in
The maximum improvement in thermal conductivity was observed in the case of mechanical stirring.
Figure
9. The sonication
maximum
improvement
in thermalin conductivity
was observed
the case of
In general,
caused
a lower improvement
thermal conductivity.
However,in
maximum
mechanical
stirring.
In general,
sonication
caused
a lower
improvement
conductivity.
improvement
in thermal
conductivity
(not shown
in Figure
9) was
observed in in
thethermal
case of sonication,
4
However,
1.6 ˆ 10maximum
% [193]. improvement in thermal conductivity (not shown in Figure 9) was observed in
the case of sonication, 1.6 × 104% [193].
18 of 37
Sn
4000
3000
2000
1000
0
BM
SM
3RM
Sn+ShM
MS
% increase in thermal
conductivity
major concern in increasing the thermal conductivity of the system [192]. The variation in thermal
conductivity with various forms of graphene and graphite nanocomposites is summarized in Table
2, and the influence of dispersion mode on the improvement of thermal conductivity is shown in
Figure 9. The maximum improvement in thermal conductivity was observed in the case of
mechanical stirring. In general, sonication caused a lower improvement in thermal conductivity.
However,
improvement in thermal conductivity (not shown in Figure 9) was observed in
Polymers
2016,maximum
8, 281
the case of sonication, 1.6 × 104% [193].
Dispersion method
Figure 9. Percent increase in thermal conductivity as a function of dispersion method (see references
Figure 9. Percent increase in thermal conductivity as a function of dispersion method (see references
in Table 2).
in Table 2).
Polymers 2016, 8, 281
17 of 35
14. Electrical Properties
14. Electrical Properties
% increase in electrical conductivity (Trillions)
Tailoring the electrical properties of graphene can unlock its many potential electronic
Tailoring the electrical properties of graphene can unlock its many potential electronic
applications
[194,195]. For example, effective gauge fields are introduced when graphene lattice
applications [194,195]. For example, effective gauge fields are introduced when graphene lattice
deformation
takestakes
place.
LikeLike
the effective
magnetic
field,field,
the produced
effective
gauge
fieldsfields
influence
deformation
place.
the effective
magnetic
the produced
effective
gauge
the Dirac
fermions
[196].
The
Fermi
level
in
undoped
graphene
lies
at
the
Dirac
point,
where
influence the Dirac fermions [196]. The Fermi level in undoped graphene lies at the Dirac point, where the
minimum
conductivity
valuesvalues
are achieved
[197].
By By
adding
free
dopants), the
the minimum
conductivity
are achieved
[197].
adding
freecharge
chargecarriers
carriers (i.e.,
(i.e., dopants),
the electrical
properties
of graphene
improved,and
and conductivity
conductivity increases
linearly
withwith
carrier
electrical
properties
of graphene
cancan
be be
improved,
increases
linearly
carrier
density
[198,199].
example,
boronas
asdopant
dopant can
carriers
perper
dopant
in a graphene
density
[198,199].
ForFor
example,
boron
can contribute
contribute~0.5
~0.5
carriers
dopant
in a graphene
[200].
Dopants
canbebeintroduced
introduced during
during the
graphene
using
chemical
vaporvapor
sheetsheet
[200].
Dopants
can
thesynthesis
synthesisofof
graphene
using
chemical
deposition (CVD) [201]. The variation in electrical conductivity with various forms of graphene and
deposition (CVD) [201]. The variation in electrical conductivity with various forms of graphene and
graphite nanocomposites is summarized in Table 3, and the influence of dispersion mode on the
graphite nanocomposites is summarized in Table 3, and the influence of dispersion mode on the
improvement of thermal conductivity is shown in Figure 10. The maximum improvement in electrical
improvement
of thermal conductivity is shown in Figure 10. The maximum improvement in electrical
conductivity was observed in the case of a combination of ball milling and mechanical stirring.
conductivity
was
inelectrical
the caseconductivities
of a combination
of in
ball
and mechanical
Therefore, bothobserved
thermal and
improved
the milling
case of mechanical
stirring. stirring.
Therefore, both thermal and electrical conductivities improved in the case of mechanical stirring.
1800000
1600000
1400000
1200000
1000000
800000
600000
400000
200000
0
Dispersion method
Figure 10. Percent increase in electrical conductivity as a function of dispersion method (see reference
in Table
3). 10. Percent increase in electrical conductivity as a function of dispersion method (see reference
Figure
in Table 3).
Polymers 2016, 8, 281
19 of 37
Table 2. A brief record of epoxy-based nanocomposites studied for improvement in thermal conductivity values.
Sr.
Authors
Year
Reinforcement (wt %)
Dispersion
method
GnP (1.9 wt %)
1
Kandre et al.
2015
SnP/(0.09 wt %)
SnW/(0.09 wt %)
9
Sn
GnP (1.9 wt %), SnP (0.09 wt %)
2
3
Tang et al.
Burger et al.
2015
2015
Chemically reduced graphene oxide (RGO) (30 wt %)
Zeng et al.
2015
5
Wang et al.
2015
Sn + MS
Zhou et al.
2015
1,400
Graphite flakes (12 wt %) (GRA-12)
237.5
Graphite flakes (15 wt %) (GRA-15)
325
Graphite flakes (14–15 wt %) (Network)
Sn + MgSr
Zeng et al.
2015
666.7
Graphite flakes (11–12 wt %) (Fiber + 1 interface)
608.3
Liquid crystal perylene bisimides polyurethane (LCPU)
modified reduced graphene oxide (RGO) (1 wt %)
GnPs, 1 µm, (GnP-C750)
237.5
Sn
Sn + MgSr + 3RM
Multi-layer graphene oxide (MGO) (2 wt %)
Aminopropyltriethoxy-silane modified Al2 O3 nanoparticles
(Al2 O3 -APS) (30 wt %)
Sn
2015
Graphite (18.4 wt %)
9
Pan et al.
2015
10
Wang et al.
2015
11
Zha et al.
2015
GNPs (3.7 wt %), Al2 O3 fibers (Afs) (65 wt %)
[203]
9.1
As the filler/matrix interfaces increase, the thermal resistance increases due to phonon scattering. In order to
improve the thermal conductivity of a composite, it is better to structure a sample with an adapted
morphology than trying to have the best dispersion. A 3D-network was first prepared with graphite foils
oriented through the thickness of the sample and then stabilized with DGEBA/DDS resin. The produced
composite sample was called as “Network”. In “fibers”, all the graphite flakes were aligned through the
thickness of sample. When a DGEBA interface layer was applied in “fiber”, the sample was called
“Fiber + 1 interface”. When two DGEBA interface layers was applied in “fiber” the sample was
called as “Fiber + 2 interfaces”.
[204]
Along with the increase in thermal conductivity, the impact and flexural strengths increased up to 68.8% and
48.5%, respectively, at 0.7 wt % LCPU/RGO.
[205]
The increase in thermal conductivity is higher in the case of larger particle size than smaller particle size.
[206]
95.5
The thermal conductivity decreases after 2 wt % MGO.
[207]
The thermal conductivity can be improved by using hybrid fillers.
[208]
The increase in thermal conductivity decreases with Al2 O3 coating of graphite.
[209]
The filler was observed to be uniformly dispersed, resulting in strong interfacial thermal resistance.
[210]
SiO2 nanoparticles are more effective in increasing thermal conductivity than GO. The maximum
improvement in thermal conductivity was observed in the case of hybrid filler.
[211]
Al2 O3 nanofibers are more effective in improving thermal conductivity than Al2 O3 nanoparticles.
[212]
106.2
59.1
Sn + MS
254.6
195.5
Sn
37.5
14.3
Sn
As-prepared nanosilica/graphene
oxide hybrid (m-SGO) (1 wt %)
GNPs (3.7 wt %), Al2 O3 nanoparticles (ANPs), (65 wt %)
(Composites produced using layer-by-layer dropping method.) The filler with large size is more effective in
increasing the thermal conductivity of epoxy because of continuous transmission of acoustic phonons and
minimum scattering at the interface due to reduced interfacial area. High intrinsic thermal conductivity of
graphene is the major reason for the obtained high thermal conductivity of nanocomposites.
68.8
SiO2 , 15 nm, (1 wt %)
GO (1 wt %)
44.4
Sn
Al2 O3 -coated graphite (Al2 O3 -graphite) (18.4 wt %)
Perylene bisimide (PBI)-hyper-branched polyglycerol
(HPG) modified reduced graphene oxide (RGO),
(PBI-HPG/RGO) (1 wt %)
[202]
50
Al2 O3 (18.4 wt %)
Tang et al.
The simultaneous inclusion of GnPs and SnP/SnW at a combined loading of 1 vol % resulted in about 40%
enhancement in the through-thickness thermal conductivity, while the inclusion of GnP at the same loading
resulted in only 9% improvement. A higher increment with simultaneous addition of GnP and SnP/SnW can
be attributed to synergistic effects.
115
Liquid-crystal perylene-bisimide polyurethane (LCPBI)
functionalized reduced graphene oxide (RGO) and
Al2 O3 -APS (LCPBI/RGO/Al2 O3 -APS)
8
775
Graphite flakes (11–12 wt %) (Fibers)
Al2 O3 nanoparticles (30 wt %)
7
1,900
1,650
Natural graphite powder (NG) (30 wt %)
GnPs, 5 µm
6
8
Ref.
40
None
Graphite flakes (11–12 wt %) (Fiber + 2 interface)
4
18
Remarks
38
GnP (1.9 wt %), SnW (0.09 wt %)
Three-dimensional graphene network (3DGNs) (30 wt %)
% Increase
in thermal
conductivity
4.8
28.6
Sn + MS
550.4
756.7
Polymers 2016, 8, 281
20 of 37
Table 2. Cont.
Reinforcement (wt %)
Dispersion
method
% Increase
in thermal
conductivity
Remarks
2015
Multi-layer graphene oxide (MGO) (2 wt %)
Sn
104.8
The thermal conductivity decreases after 2 wt % MGO.
[213]
2015
GNPs (8 wt %)
MS
627
The thermal conductivity increases with GNPs at the loss of Vickers microhardness after 1 wt % of GNP.
[214]
21.8
The thermal conductivity decreases after 1 wt % RGO. The silica layer on S-graphene makes electrically
conducting graphene insulating, reduces the modulus mismatch between the filler and matrix, and improves
the interfacial interactions of the nanocomposites, which results in enhanced thermal conductivity.
[215]
The maximum improvement in thermal conductivity was observed in the case of graphene sheets with
thickness of 1.5 nm.
[216]
The alignment of MLG causes an exceptional improvement in thermal conductivity and exceeds other
filler-based epoxy nanocomposites.
[193]
Ball milling is more effective in improving the thermal conductivity of GNP/epoxy than sonication. The
thermal conductivity decreases when ball milling is carried out for more than 30 h.
[126]
The thermal conductivity decreases with increasing wt % of NG after 1 wt %. The thermal conductivity
decreases after 2 wt % of GNPs. The maximum improvement in thermal conductivity was observed with
expanded graphite.
[217]
14
The thermal conductivity increases with increasing temperature.
[73]
240
High aspect ratio of GNPs and oxygen functional groups play a significant role in improving thermal
conductivity of nanocomposites.
[218]
The existence of the intermediate silica layer enhances the interfacial attractions between TRGO and epoxy
and improved dispersion state, which caused a significant increase in thermal conductivity.
[219]
Silane functionalization can significantly improve thermal conductivity of GNP/epoxy.
[220]
The thermal conductivity increases with increasing particle size. The particle size distribution significantly
influences the thermal conductivity. GNPs with a broad particle size distribution gave higher thermal
conductivity than the particles with a narrow particle size distribution, due to the availability of smaller
particles that can bridge gaps between larger particles.
[221]
The increase in thermal conductivity decreases with Al(OH)3 coating on GO.
[222]
Sr.
Authors
Year
12
Zhou et al.
13
Wang et al.
14
Pu et al.
2014
RGO (1 wt %)
3-aminopropyl triethoxysilane (APTES) functionalized
graphene oxide (A-graphene) (8 wt %)
Sn + MgSr
47.1
Silica-coated A-graphene (S-graphene) (8 wt %)
76.5
Graphite (44.30 wt %)
888.2
15
Fu et al.
2014
Graphite nanoflakes (16.81 wt %)
MS
982.3
16
Li et al.
2014
Aligned MLG (AG) (11.8 wt %)
Sn
16670
17
Guo and Chen
2014
GNPs (25 wt %)
Sn
780
GNPs (25 wt %)
BM
1420
Graphene sheets (10.10 wt %)
18
Corcione and
Maffezzoli
2258.8
Natural graphite (NG) (1 wt %)
2013
GNPs (2 wt %)
24.1
Sn
Expanded graphite (EGS) (3 wt %)
19
20
Chandrasekaran et al.
Min et al.
2013
2013
GNP (2 wt %)
GNPs (5 wt %)
Hsiao et al.
2013
Thermally reduced graphene oxide (TRGO) (1 wt %)
3RM
Sn
19
Sn + ShM
Silica nanosheets (Silica-NS) (1 wt %)
22
Zhou et al.
2013
24
Raza et al.
Kim et al.
2012
2012
26.5
37.5
TRGO-silica-NS (1 wt %)
61.5
Untreated GNPs (12 wt %)
139.3
Silane-treated COOH-MWCNTs (6 wt %)
Sn + MgSr
Silane-treated GNPs (6 wt %)
23
89.8
232.1
Silica (1 wt %)
21
192.9
525
GNPs, 5 µm, 30 wt %, in rubbery epoxy
MS
GNPs, 5 µm, 20 wt %, in rubbery epoxy
ShM
332.6
GNPs, 15 µm, 25 wt %, in rubbery epoxy
MS
1228.4
GNPs, 15 µm, 25 wt %, in rubbery epoxy
ShM
1118.2
GNPs, 20 µm, 20 wt %, in rubbery epoxy
ShM
684.6
GNPs, 20 µm, 12 wt %, in glassy epoxy
ShM
567.6
GNPs, 15 µm, 20 wt %, in glassy epoxy
MS
GO (3 wt %)
Al(OH)3 -coated graphene oxide (Al-GO) (3 wt %)
Ref.
Sn
818.6
683
90.4
35.1
Polymers 2016, 8, 281
21 of 37
Table 2. Cont.
Sr.
Authors
Year
Reinforcement (wt %)
Dispersion
method
% Increase
in thermal
conductivity
Remarks
Ref.
25
Chatterjee et
al.
2012
Amine functionalized expanded graphene nanoplatelets
(EGNPs) (2 wt %)
Sn + 3RM
36
The EGNPs form a conductive network in the epoxy matrix allowing for increased thermal conductivity.
[83]
26
Im and Kim
2012
111
The thermal conductivity decreases after 50 wt %, which can be attributed to residual epoxy that forms an
insulting layer on reinforcement. MWCNT helps the formation of 3D network structure.
[223]
The increase in thermal conductivity decreases with Al(OH)3 coating of GO.
[224]
GNPs are more effective in improving thermal conductivity than MWNTs. The maximum improvement in
thermal conductivity was observed in the case of hybrid fillers.
[225]
GNPs showed a significantly greater increase in thermal conductivity than MWNTs. The maximum
improvement in thermal conductivity is shown by non-covalent functionalized GNS, which can be attributed
to high surface area and uniform dispersion of GNS.
[114]
The layered structure of MWNTs enables an efficient phonon transport through the inner layers, while SWNTs
present a higher resistance to heat flow at the interface, due to its higher surface area. The f-MWNTs have
functional groups on their surface, acting as scattering points for the phonon transport.
[226]
The thermal conductivity increases exponentially with increasing wt % of graphene flakes.
[227]
The thermal conductivity increases with chemical functionalization.
[177]
The hybrid filler demonstrates a strong synergistic effect and surpasses the performance of the individual
SWNT and GNP filler.
[228]
Thermally conductive graphene oxide (GO) (50 wt %)
Sn
Thermally conductive graphene oxide (GO) (50 wt %),
MWCNTs (0.36 wt %)
27
Heo et al.
2012
Al2 O3 (80 wt %), GO (5 wt %)
203.4
3RM
Al(OH)3 -coated GO (5 wt %)
MWNTs (65 wt %)
28
29
Huang et al.
Teng et al.
2012
2011
GNPs (65 wt %)
1,100
MS
Gallego et al.
2011
3,600
MWNT (4 wt %)
160
GNPs(4 wt %)
Sn
860
MWNTs (1 wt %) in nanofluids
66.7
SWNTs (0.6 wt %) in nanofluids
20
ShM
32
Ganguli et al.
2011
2008
GO (1 wt %) in nanofluids
0
MWNTs(1 wt %) in nanocomposites
72.7
Graphene flakes (12 wt %)
Exfoliated graphite flakes (20 wt %)
63.6
Sn
SM
Chemically functionalized graphite flakes (20 wt %)
Yu et al.
2008
SWNTs (10 wt %)
350
2,087.2
2,907.2
Carbon black (CB) (10 wt %)
33
20
0
Functionalized graphene sheet (FGS) (1 wt %) in
nanocomposites
Tien et al.
700
Poly(glycidyl methacrylate containing localized pyrene
groups (Py-PGMA) functionalized GNPs (Py-PGMA-GNS)
Functionalized graphene sheet (FGS) (1 wt %) in nanofluids
31
2,750
MWNTs (38 wt %), GNPs (38 wt %)
f-MWNTs (0.6 wt %) in nanofluids
30
1,650
1,450
75
Sn + ShM
125
GNPs (10 wt %)
625
GNPs (7.5 wt %), SWNTs (2.5 wt %)
775
Polymers 2016, 8, 281
22 of 37
Table 3. A brief record of epoxy-based nanocomposites studied for improvement in electrical conductivity values. HSM: high speed mixing.
Sr.
Authors
Year
1
Wu et al.
2015
Reinforcement/wt %
Dispersion
method
% Increase
in electrical
conductivity
GNPs (1.5 wt %), transverse to alignment
Sn + 3RM
1 ˆ 107
GNPs (3 wt %), randomly oriented
1 ˆ 108
GNPs (3 wt %), parallel to alignment
1 ˆ 1010
Remarks
Ref.
The maximum thermal conductivity was observed in the case of
aligned GNPs.
[229]
2
Liu et al.
2015
Graphene woven fabric (GWF) (0.62 wt %)
None.
1 ˆ 1013
(Samples were produced using resin infiltration.) The average
number of graphene layers in GWFs varied between 4 and 12.
[230]
3
Ming et al.
2015
Graphene foam (GF) (80 wt %)
None.
8 ˆ 102
(Samples were produced using hot pressing.) The electrical
conductivity of pure graphene foam (GF) is 2.9 S-cm-1 , which is
much lower than graphene, which can be because of the presence
of structural defects.
[231]
5
Ghaleb et al.
2014
GNPs are more effective in improving the thermal conductivity of
epoxy than MWCNTs.
[159]
The surface functionalization of GO can significantly improve the
electrical conductivity of GO–epoxy.
[232]
4.13 ˆ 102
Ag–graphene can be used in electronic applications due to its high
electrical conductivity.
[233]
1 ˆ 1018
The surface functionalization significantly improves electrical
conductivity.
[234]
2.08 ˆ 105
The samples were produced using chloroform.
[235]
1.16 ˆ 105
The samples were produced using tetrahydrofuran.
The samples were produced using dimethylformamide.
[189]
3RM is more effective in improving the electrical conductivity of
epoxy than sonication and high speed shear mixing.
[73]
The electrical conductivity significantly increases with hybrid filler.
[236]
GNPs (1.1 wt %)
Sn
MWCNTs (1.9 wt %)
6
Tang et al.
2014
GO (5 wt %)
Sn + HSM
Diamine polyetheramine functionalized
GO (GO-D230) (5 wt %)
7
Dou et al.
2014
8
Tang et al.
2014
Silver plated graphene (Ag-G) (25 wt %)
GO (3.6 wt %)
Monti et al.
2013
GNPs (3 wt %)
Sn + MS
Sn
11
Wajid et al.
Chandrakekaran et al.
2013
2013
Sn + MS
Suherman et al.
2013
1012
1017
GNPs (0.24 wt %)
Sn + MS
2.22 ˆ 103
GNPs (1 wt %)
Sn + ShM
1ˆ
104
GNPs (2 wt %)
3RM
1 ˆ 108
GNPs (80 wt %), CNTs (5 wt %),
through-plane
12
1.92 ˆ 109
1ˆ
GNPs (3 wt %)
10
1.62 ˆ 105
1.92 ˆ
Polyetheramine refluxed GO (GO-D2000)
(3.6 wt %)
9
1.39 ˆ 106
GNPs (80 wt %), CNTs (5 wt %), in-plane
7.30 ˆ 1017
BM + MS
1.80 ˆ 1018
GNPs (80 wt %), through-plane
4 ˆ 1017
GNPs (80 wt %) in-plane
5 ˆ 1017
Polymers 2016, 8, 281
23 of 37
Table 3. Cont.
Sr.
Authors
Year
Reinforcement/wt %
Dispersion
method
GO (0.5 wt %)
13
Mancinelli et al.
2013
GO (0.5 wt %)
Octadecylamine (ODA)-treated partially
reduced and chemically modified GO (MGO)
(0.5 wt %)
GO (0.5 wt %)
14
15
Al-Ghamdi et al.
Kim et al.
2013
2012
Sn
Heo et al.
2012
18
Tien et al.
Fan et al.
2011
2009
240
The conductivity was measured before post-curing.
730
The conductivity was measured after post-curing.
550
The conductivity was reduced after functionalization.
Ref.
[237]
Two phase
extraction
240
The system was not fully cured during curing process.
7.80 ˆ 103
The conductivity significantly increased after post-curing.
Foliated graphite nanosheets (FGNs) (40 wt %)
Centrifugal mixing
9.90 ˆ 103
Dielectric properties of epoxy–FGN composites decreased with an increase in frequency.
[238]
Al(OH)3 functionalized GO (Al-GO) (3 wt %)
MS + MgSr
The increase in electrical conductivity decreases with Al(OH)3 functionalization of GO.
[239]
[224]
4.90 ˆ 103
The increase in electrical conductivity with Al(OH)3 functionalization decreased. The electrically
insulating Al(OH)3 on the graphene oxide nanosheet can prevent electron tunneling and act as ion
traps which block ion mobility, resulting in a decrease in the electrical properties of nanocomposites.
4 ˆ 107
The percolation threshold was 8 wt %.
[227]
The maximum electrical conductivity was observed in the case of hybrid fillers.
[240]
Al2 O3 (80 wt %), Al(OH)3 functionalized GO
(Al-GO) (5 wt %)
Graphite flakes (14 wt %)
GNPs (5 wt %)
75
115
3RM
Al2 O3 (80 wt %), GO (5 wt %)
17
Remarks
GO (0.5 wt %)
GO (3 wt %)
16
% Increase
in electrical
conductivity
Sn
Sn + MS
GNPs (4.5 wt %), carbon black (CB) (0.5 wt %)
2.90 ˆ 103
5.50 ˆ 1010
5.50 ˆ 1012
19
Jovic et al.
2008
Expanded graphite (EG) (8 wt %)
Sn
5.50 ˆ 1017
The electrical conductivity further increases with the application of electric field.
[241]
20
Li et al.
2007
MWCNTs (1 wt %)
Sn
4.63 ˆ 107
The samples were produced using acetone.
[242]
21
Pecastaings et al.
2004
MWCNTs (20 wt %)
Sn + MS
4.53 ˆ 103
The samples were produced using acetone.
[243]
Polymers 2016, 8, 281
24 of 37
15. Conclusions
The following are the key points related to epoxy/graphene nanocomposites:
1.
2.
3.
4.
5.
6.
7.
Epoxy is an excellent matrix for graphene composites because of its efficient properties such as
enhancement in composite mechanical properties, processing flexibility, and acceptable cost [2].
Graphene can significantly enhance the fracture toughness of epoxy nanocomposites—i.e., up to
131% [59]. When epoxy is reinforced with graphene, the carbonaceous sheets shackle the crack
and restrict its advancement. This obstruction and deflection of the crack by the graphene at the
interface is the foremost mechanism of raising the fracture toughness of nanocomposites.
The graphene sheets with smaller length, width, and thickness are more efficient in improving
the fracture toughness than those with larger dimensions [57]. Large graphene sheets have a
high stress concentration factor, because of which crack generation becomes easy in the epoxy
matrix [118,119]. The cracks deteriorate the efficiency of graphene in enhancing the fracture
toughness of epoxy/graphene nanocomposites.
Uniformly dispersed graphene improves fracture toughness significantly as compared to the
poorly dispersed graphene [72]. It is evident from the published literature that the fracture
toughness dropped when graphene weight fraction was increased beyond 1 wt %. The decrease in
fracture toughness with higher weight fraction of graphene can be correlated with the dispersion
state of graphene. As graphene weight fraction increases beyond 1 wt %, the dispersion state
becomes inferior.
Three roll milling or calendering process is an efficient way of dispersing the reinforcement into a
polymer matrix, as it involves high shear forces [244–248]. However, the maximum enhancement
in fracture toughness was achieved with a combination of sonication and mechanical stirring [59].
In thermosetting materials such as epoxy, high crosslink density is desirable for improved
mechanical properties. However, fracture toughness is dropped with high crosslinking [57].
The literature has proved the absence of consensus of graphene’s role in improving the mechanical
properties of nanocomposites [150–154]. Generally, graphene acts as panacea and raises the
mechanical properties [116,155–158]. On the contrary, it acts as placebo and shows no effect on
mechanical properties. Even worse, it is inimical and razes the mechanical properties [160–164].
The main factors that dictate graphene’s influence on the mechanical properties of epoxy
nanocomposites include topographical features, morphology, weight fraction, dispersion state,
surface modifications, and interfacial interactions.
Acknowledgments: The authors would like to thank the Department of Mechanical and Construction Engineering,
Northumbria University, UK for the provision of research facilities, without which the analysis of relevant data
was not possible.
Author Contributions: Rasheed Atif compiled the literature and wrote the manuscript. Islam Shyha and
Fawad Inam supervised the project and proofread the manuscript.
Conflicts of Interest: The authors declare no conflict of interest.
Abbreviations
The following abbreviations are used in this manuscript:
Polymers 2016, 8, 281
3DGN
3RM
A
APTS-GO
ATGO
ATP
ATS
BM
CM
CNF
CNFs
CNTs
DDS
DGEBA-f-GO
DRA
DRTi
EGNPs
EMCs
fGnPs
GF
G-NH2
GnPs
GNPs*
GNs
GNSs
GO
GP
GPLs
GPTS-GO
G-Si
HPH + 3RM
HSM
m-clay
m-CNFs
MERGO
m-GnP
m-GnP*
m-GP
MgSr
MLG
MS
MS + USn
MWCNTs
MWNTs
ND
P
p-CNFs
PEA
phr
PMCs
Q/I
RGO
SA
SATPGO
SCFs
ShM
Silane-f-GO
SM
Sn
Sn + BM
Sn + MgSr
Sn + MS
SnP
SnW
SWCNTs
SWNTs
TEM
TPE
UG
U-GnP
USn
25 of 37
Three dimensional graphene network
Three roll milling
Aramid fibers
Amino-functionalized graphene oxide (GO)
3-Aminopropyltriethoxysilane functionalized silica nanoparticles attached GO
Attapulgite
3-amino functionalized silica nanoparticles
Ball milling
Centrifugal mixing
Carbon nanofiber
Vapor grown carbon nanofibers
Carbon nanotubes
Diaminodiphenylsulfone
Diglycidyl ether of bisphenol-A functionalized GO
Discontinuously reinforced aluminum
Discontinously reinforced titanium
Amine functionalized expanded graphene nanoplatelets
Epoxy matrix composites
Polybenzimidazole functionalized graphene platelets (GnPs)
Graphene foam
Amino-functionalized GNPs
Graphene platelets
Graphite nanoplatelets
Amine functionalized graphene sheets
Graphene nanosheets
Graphene oxide
Graphite particles
Graphene nanoplatelets
Epoxy functionalized GO
Silane modified GNPs
High pressure homogenizer + three roll milling
High speed mixing
Surface modified nano clay
Triazole functionalized carbon nanofibers
Microwave exfoliated reduced graphene oxide
Surface modified GnP
Surfactant modified graphene platelets
Surface modified graphene platelets
Magnetic stirring
Multi-layer graphene
Mechanical stirring
Mechanical stirring + Ultrasonication
Multi-walled carbon nanotubes
Multi-walled carbon nanotubes
Nanodiamond
Polyacrylonitrile (PAN) fibers
Pristine carbon nanofibers
Polyetheramine
Per hundred parts of resin
Polymer matrix composites
Quasi-isotropic
Thermally reduced graphene oxide
Surface area
3-Aminopropyltriethoxysilane modified silica nanoparticles attached graphene oxide
Short carbon fibers
Shear mixing
Silane functionalized GO
Speed mixing
Sonication
Sonication + Ball milling
Sonication + Magnetic stirring
Sonication + Mechanical stirring
Silver nanoparticles
Silver nanowires
Single-walled carbon nanotubes
Single-walled carbon nanotubes
Transmission electron microscopy
Two phase extraction
Unmodified graphene nanoplatelets
Unmodified graphene platelets
Ultrasonication
Polymers 2016, 8, 281
26 of 37
References
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
13.
14.
15.
16.
17.
18.
19.
20.
21.
Carlson, R.L.; Kardomateas, G.A.; Craig, J.I. Mechanics of Failure Mechanisms in Structures, 1st ed.; Springer:
Berlin, Germany, 2012.
Miracle, D.B., Donaldson, S.L., Eds.; ASM Handbook Volume 21: Composites; ASM International: Materials
Park, OH, USA, 2001.
Yao, X.F.; Zhou, D.; Yeh, H.Y. Macro/microscopic fracture characterizations of SiO2 /epoxy nanocomposites.
Aerosp. Sci. Technol. 2008, 12, 223–230. [CrossRef]
Wetzel, B.; Rosso, P.; Haupert, F.; Friedrich, K. Epoxy nanocomposites—Fracture and toughening mechanisms.
Eng. Fract. Mech. 2006, 73, 2375–2398. [CrossRef]
Naous, W.; Yu, X.Y.; Zhang, Q.X.; Naito, K.; Kagawa, Y. Morphology, tensile properties, and fracture
toughness of epoxy/Al2 O3 nanocomposites. J. Polym. Sci. Part B 2006, 44, 1466–1473. [CrossRef]
Kim, B.C.; Park, S.W.; Lee, D.G. Fracture toughness of the nano-particle reinforced epoxy composite.
Compos. Struct. 2008, 86, 69–77. [CrossRef]
Wang, K.; Chen, L.; Wu, J.; Toh, M.L.; He, C.; Yee, A.F. Epoxy nanocomposites with highly exfoliated clay:
Mechanical properties and fracture mechanisms. Macromolecules 2005, 38, 788–800. [CrossRef]
Liu, W.; Hoa, S.V.; Pugh, M. Fracture toughness and water uptake of high-performance epoxy/nanoclay
nanocomposites. Compos. Sci. Technol. 2005, 65, 2364–2373. [CrossRef]
Gojny, F.H.; Wichmann, M.H.G.; Köpke, U.; Fiedler, B.; Schulte, K. Carbon nanotube-reinforced
epoxy-composites: Enhanced stiffness and fracture toughness at low nanotube content. Compos. Sci. Technol.
2004, 64, 2363–2371. [CrossRef]
Yu, N.; Zhang, Z.H.; He, S.Y. Fracture toughness and fatigue life of MWCNT/epoxy composites. Mater. Sci.
Eng. A 2008, 494, 380–384. [CrossRef]
Srikanth, I.; Kumar, S.; Kumar, A.; Ghosal, P.; Subrahmanyam, C. Effect of amino functionalized MWCNT on
the crosslink density, fracture toughness of epoxy and mechanical properties of carbon-epoxy composites.
Compos. Part. A Appl. Sci. Manuf. 2012, 43, 2083–2086. [CrossRef]
Mathews, M.J.; Swanson, S.R. Characterization of the interlaminar fracture toughness of a laminated
carbon/epoxy composite. Compos. Sci. Technol. 2007, 67, 1489–1498. [CrossRef]
Arai, M.; Noro, Y.; Sugimoto, K.I.; Endo, M. Mode-I and mode II interlaminar fracture toughness of CFRP
laminates toughened by carbon nanofiber interlayer. Compos. Sci. Technol. 2008, 68, 516–525. [CrossRef]
Wong, D.W.Y.; Lin, L.; McGrail, P.T.; Peijs, T.; Hogg, P.J. Improved fracture toughness of carbon fibre/epoxy
composite laminates using dissolvable thermoplastic fibres. Compos. Part. A 2010, 41, 759–767. [CrossRef]
Novoselov, K.S.; Geim, A.K.; Morozov, S.V.; Jiang, D.; Zhang, Y.; Dubonos, S.V.; Grigorieva, I.V.; Firsov, A.A.
Electric Field Effect in Atomically Thin Carbon Films. Science 2004, 306, 666–669. [CrossRef] [PubMed]
Pokharel, P.; Truong, Q.-T.; Lee, D.S. Multi-step microwave reduction of graphite oxide and its use in
the formation of electrically conductive graphene/epoxy composites. Compos. Part B 2014, 64, 187–193.
[CrossRef]
Tian, M.; Qu, L.; Zhang, X.; Zhang, K.; Zhu, S.; Guo, X.; Han, G.; Tang, X.; Sun, Y. Enhanced mechanical and
thermal properties of regenerated cellulose/graphene composite fibers. Carbohydr. Polym. 2014, 111, 456–462.
[CrossRef] [PubMed]
Xu, Z.; Zhang, J.; Shan, M.; Li, Y.; Li, B.; Niu, J.; Zhou, B.; Qian, X. Organosilane-functionalized graphene oxide
for enhanced antifouling and mechanical properties of polyvinylidene fluoride ultrafiltration membranes.
J. Membr. Sci. 2014, 458, 1–13. [CrossRef]
Bkakri, R.; Sayari, A.; Shalaan, E.; Wageh, S.; Al-Ghamdi, A.A.; Bouazizi, A. Effects of the graphene
doping level on the optical and electrical properties of ITO/P3HT:Graphene/Au organic solar cells.
Superlattices Microstruct. 2014, 76, 461–471. [CrossRef]
Lian, Y.; He, F.; Wang, H.; Tong, F. A new aptamer/graphene interdigitated gold electrode piezoelectric
sensor for rapid and specific detection of staphylococcus aureus. Biosens. Bioelectron. 2014, 65, 314–319.
[CrossRef] [PubMed]
Abdin, Z.; Alim, M.A.; Saidur, R.; Islam, M.R.; Rashmi, W.; Mekhilef, S.; Wadi, A. Solar energy harvesting
with the application of nanotechnology. Renew. Sustain. Energy Rev. 2013, 26, 837–852. [CrossRef]
Polymers 2016, 8, 281
22.
23.
24.
25.
26.
27.
28.
29.
30.
31.
32.
33.
34.
35.
36.
37.
38.
39.
40.
41.
42.
43.
44.
45.
46.
27 of 37
Sun, W.; Hu, R.; Liu, H.; Zeng, M.; Yang, L.; Wang, H.; Zhu, M. Embedding nano-silicon in graphene
nanosheets by plasma assisted milling for high capacity anode materials in lithium ion batteries.
J. Power Sources 2014, 268, 610–618. [CrossRef]
Azeez, A.A.; Rhee, K.Y.; Park, S.J.; Hui, D. Epoxy clay nanocomposites—Processing, properties and
applications: A review. Compos. Part. B 2013, 45, 308–320. [CrossRef]
Aziz, A.; Lim, H.N.; Girei, S.H.; Yaacob, M.H.; Mahdi, M.A.; Huang, N.M.; Pandikumar, A. Silver/graphene
nanocomposite-modified optical fiber sensor platform for ethanol detection in water medium. Sens. Actuators
B Chem. 2015, 206, 119–125.
Agnihotri, N.; Chowdhury, A.D.; De, A. Non-enzymatic electrochemical detection of cholesterol using
β-cyclodextrin functionalized graphene. Biosens. Bioelectron. 2015, 63, 212–217. [CrossRef] [PubMed]
Galpaya, D.; Wang, M.; Liu, M.; Motta, N.; Waclawik, E.; Yan, C. Recent Advances in fabrication and
characterization of graphene-polymer nanocomposites. Sci. Res. 2012, 2012, 30–49. [CrossRef]
Shahil, K.M.F.; Balandin, A.A. Thermal properties of graphene and multilayer graphene: Applications in
thermal interface materials. Solid State Commun. 2012, 152, 1331–1340. [CrossRef]
Al-Saleh, M.H.; Sundararaj, U. Review of the mechanical properties of carbon nanofiber/polymer composites.
Compos. Part A 2011, 42, 2126–2142. [CrossRef]
Sanjinés, R.; Abad, M.D.; Vâju, C.; Smajda, R.; Mionić, M.; Magrez, A. Electrical properties and applications
of carbon based nanocomposite materials: An overview. Surf. Coat. Technol. 2011, 206, 727–733. [CrossRef]
Potts, J.R.; Dreyer, D.R.; Bielawski, C.W.; Ruoff, R.S. Graphene-based polymer nanocomposites.
Polymer (Guildf) 2011, 52, 5–25. [CrossRef]
Qin, F.; Brosseau, C. A review and analysis of microwave absorption in polymer composites filled with
carbonaceous particles. J. Appl. Phys. 2012. [CrossRef]
Lee, S.-Y.; Park, S.-J. Comprehensive review on synthesis and adsorption behaviors of graphene-based
materials. Carbon Lett. 2012, 13, 73–87. [CrossRef]
Singh, V.; Joung, D.; Zhai, L.; Das, S.; Khondaker, S.I.; Seal, S. Graphene-based materials: Past, present and
future. Prog. Mater. Sci. 2011, 56, 1178–1271. [CrossRef]
Van Rooyen, L.J.; Karger-Kocsis, J.J.; Kock, L.D.; David Kock, L. Improving the helium gas barrier properties
of epoxy coatings through the incorporation of graphene nanoplatelets and the influence of preparation
techniques. J. Appl. Polym. Sci. 2015, 42584, 1–13. [CrossRef]
Kim, H.; Abdala, A.A.; Macosko, C.W. Graphene/polymer nanocomposites. Macromolecules 2010, 43,
6515–6530. [CrossRef]
Dhand, V.; Rhee, K.Y.; Kim, H.J.; Jung, D.H. A comprehensive review of graphene nanocomposites: research
status and trends. J. Nanomater. 2015, 2013, 1–15. [CrossRef]
Santamaria, A.; Muñoz, M.E.; Fernández, M.; Landa, M. Electrically conductive adhesives with a focus on
adhesives that contain carbon nanotubes. J. Appl. Polym. Sci. 2013, 129, 1643–1652. [CrossRef]
Yang, M.-Q.; Xu, Y.-J. Selective photoredox using graphene-based composite photocatalysts. Phys. Chem.
Chem. Phys. 2013, 15, 19102–19118. [CrossRef] [PubMed]
Srinivas, G.; Guo, Z.X. Graphene-based materials: Synthesis and gas sorption, storage and separation.
Prog. Mater. Sci. 2014. [CrossRef]
Xu, Z.; Chen, L.; Zhou, B.; Li, Y.; Li, B.; Niu, J.; Shan, M.; Guo, Q.; Wang, Z.; Qian, X. Nano-structure and
property transformations of carbon systems under γ-ray irradiation: A review. RSC Adv. 2013. [CrossRef]
Hu, K.; Kulkarni, D.D.; Choi, I.; Tsukruk, V.V. Graphene-polymer nanocomposites for structural and
functional applications. Prog. Polym. Sci. 2014, 39, 1934–1972. [CrossRef]
Young, R.J.; Kinloch, I.A.; Gong, L.; Novoselov, K.S. The mechanics of graphene nanocomposites: A review.
Compos. Sci. Technol. 2012, 72, 1459–1476. [CrossRef]
Zaman, I.; Manshoor, B.; Khalid, A.; Araby, S. From clay to graphene for polymer nanocomposites—A survey.
J. Polym. Res. 2014, 21, 429. [CrossRef]
Sun, X.; Sun, H.; Li, H.; Peng, H. Developing polymer composite materials: Carbon nanotubes or graphene?
Adv. Mater. 2013, 25, 5153–5176. [CrossRef] [PubMed]
Kuilla, T.; Bhadra, S.; Yao, D.; Kim, N.H.; Bose, S.; Lee, J.H. Recent advances in graphene-based polymer
composites. Prog. Polym. Sci. 2010, 35, 1350–1375. [CrossRef]
Rasheed, A.; Khalid, F.A. Fabrication and properties of CNTs reinforced polymeric matrix nanocomposites
for sports applications. IOP Conf. Ser. Mater. Sci. Eng. 2014. [CrossRef]
Polymers 2016, 8, 281
47.
48.
49.
50.
51.
52.
53.
54.
55.
56.
57.
58.
59.
60.
61.
62.
63.
64.
65.
66.
67.
68.
69.
70.
71.
28 of 37
Yue, L.; Pircheraghi, G.; Monemian, S.A.; Manas-Zloczower, I. Epoxy composites with carbon nanotubes and
graphene nanoplatelets—Dispersion and synergy effects. Carbon 2014, 78, 268–278. [CrossRef]
Jean-Pierre, P.; Roberto, W. Epoxy Polymers New Materials and Innovations; Wiley-VCH: Weinheim,
Germany, 2010.
Sanjay, M. Composites Manufacturing Materials, Product, and Process Engineering; CRC Press: Boca Raton, FL,
USA, 2002.
Valery, V.; Evgeny, M. Mechanics and Analysis of Composite Materials; Elsevier: Amsterdam, The Netherlands, 2001.
Atif, R.; Inam, F. Influence of macro-topography on damage tolerance and fracture toughness of monolithic
epoxy for tribological applications. World J. Eng. Technol. 2016, 4, 335–360. [CrossRef]
Wongbong, C.; Jo-Won, L. Graphene Synthesis and Applications; CRC Press: Boca Raton, FL, USA, 2012.
Warner, J.H.; Fransizka, S.; Mark, R.; Bachmatiuk, A. Graphene: Fundamentals and Emergent Applications;
Elsevier: Amsterdam, The Netherlands, 2013.
Mikhail, K.; Iosifovich, K.M. Graphene: Carbon in Two Dimensions; Cambridge University Press: Cambridge,
UK, 2012.
Wolf, E.L. Graphene: A New Paradigm in Condensed Matter and Device Physics; OUP: Oxford, UK, 2013.
Quintana, M.; Spyrou, K.; Grzelczak, M.; Browne, W.R.; Rudolf, P.; Prato, M. Functionalization of graphene.
ACS Nano 2010, 4, 3527–3533. [CrossRef] [PubMed]
Wang, X.; Jin, J.; Song, M. An investigation of the mechanism of graphene toughening epoxy. Carbon 2013,
65, 324–333. [CrossRef]
Jia, J.; Kan, C.-M.; Lin, X.; Shen, X.; Kim, J.-K. Effects of processing and material parameters on synthesis of
monolayer ultralarge graphene oxide sheets. Carbon 2014, 77, 244–254. [CrossRef]
Ma, J.; Meng, Q.; Zaman, I.; Zhu, S.; Michelmore, A.; Kawashima, N.; Wang, C. H.; Kuan, H.-C. Development
of polymer composites using modified, high-structural integrity graphene platelets. Compos. Sci. Technol.
2014, 91, 82–90. [CrossRef]
Loomis, J.; Panchapakesan, B. Dimensional dependence of photomechanical response in carbon
nanostructure composites: A case for carbon-based mixed-dimensional systems. Nanotechnology 2012,
23. [CrossRef] [PubMed]
Karger-Kocsis, J.; Mahmood, H.; Pegoretti, A. Recent advances in fiber/matrix interphase engineering for
polymer composites. Prog. Mater. Sci. 2015, 73, 1–43. [CrossRef]
Dieter, G.E. Mechanical Metallurgy, SI Metric ed.; McGraw-Hill: New York, NY, USA, 1988.
Wan, Y.-J.; Tang, L.-C.; Gong, L.-X.; Yan, D.; Li, Y.-B.; Wu, L.-B.; Jiang, J.-X.; Lai, G.-Q. Grafting of epoxy
chains onto graphene oxide for epoxy composites with improved mechanical and thermal properties. Carbon
2014, 69, 467–480. [CrossRef]
Bindu Sharmila, T.K.; Nair, A.B.; Abraham, B.T.; Beegum, P.M.S.; Thachil, E.T. Microwave exfoliated
reduced graphene oxide epoxy nanocomposites for high performance applications. Polymer (Guildf) 2014, 55,
3614–3627.
Zhang, Y.; Wang, Y.; Yu, J.; Chen, L.; Zhu, J.; Hu, Z. Tuning the interface of graphene platelets/epoxy
composites by the covalent grafting of polybenzimidazole. Polymer (Guildf) 2014, 55, 4990–5000. [CrossRef]
Ahmadi-Moghadam, B.; Sharafimasooleh, M.; Shadlou, S.; Taheri, F. Effect of functionalization of graphene
nanoplatelets on the mechanical response of graphene/ epoxy composites. Mater. Des. 2014, 66, 142–149.
[CrossRef]
Chandrasekaran, S.; Sato, N.; Tölle, F.; Mülhaupt, R.; Fiedler, B.; Schulte, K. Fracture toughness and failure
mechanism of graphene-based epoxy composites. Compos. Sci. Technol. 2014, 97, 90–99. [CrossRef]
Wan, Y.-J.; Gong, L.-X.; Tang, L.-C.; Wu, L.-B.; Jiang, J.-X. Mechanical properties of epoxy composites filled
with silane-functionalized graphene oxide. Compos. Part A 2014, 64, 79–89. [CrossRef]
Zaman, I.; Manshoor, B.; Khalid, A.; Meng, Q.; Araby, S. Interface modification of clay and graphene platelets
reinforced epoxy nanocomposites: A comparative study. J. Mater. Sci. 2014, 49, 5856–5865. [CrossRef]
Jiang, T.; Kuila, T.; Kim, N.H.; Lee, J.H. Effects of surface-modified silica nanoparticles attached graphene
oxide using isocyanate-terminated flexible polymer chains on the mechanical properties of epoxy composites.
J. Mater. Chem. A 2014. [CrossRef]
Shokrieh, M.M.; Ghoreishi, S.M.; Esmkhani, M.; Zhao, Z. Effects of graphene nanoplatelets and graphene
nanosheets on fracture toughness of epoxy nanocomposites. Fatigue Fract. Eng. Mater. Struct. 2014, 37,
1116–1123.
Polymers 2016, 8, 281
72.
73.
74.
75.
76.
77.
78.
79.
80.
81.
82.
83.
84.
85.
86.
87.
88.
89.
90.
91.
92.
29 of 37
Tang, L.-C.; Wan, Y.-J.; Yan, D.; Pei, Y.-B.; Zhao, L.; Li, Y.-B.; Wu, L.-B.; Jiang, J.-X.; Lai, G.-Q. The effect of
graphene dispersion on the mechanical properties of graphene/epoxy composites. Carbon 2013, 60, 16–27.
[CrossRef]
Chandrasekaran, S.; Seidel, C.; Schulte, K. Preparation and characterization of graphite nano-platelet
(GNP)/epoxy nano-composite: Mechanical, electrical and thermal properties. Eur. Polym. J. 2013, 49,
3878–3888. [CrossRef]
Li, Z.; Wang, R.; Young, R.J.; Deng, L.; Yang, F.; Hao, L.; Jiao, W.; Liu, W. Control of the functionality of
graphene oxide for its application in epoxy nanocomposites. Polymer (Guildf) 2013, 54, 6437–6446. [CrossRef]
Shadlou, S.; Alishahi, E.; Ayatollahi, M.R. Fracture behavior of epoxy nanocomposites reinforced with
different carbon nano-reinforcements. Compos. Struct. 2013, 95, 577–581. [CrossRef]
Jiang, T.; Kuila, T.; Kim, N.H.; Ku, B.-C.; Lee, J.H. Enhanced mechanical properties of silanized silica
nanoparticle attached graphene oxide/epoxy composites. Compos. Sci. Technol. 2013, 79, 115–125. [CrossRef]
Liu, W.; Kong, J.; Toh, W.E.; Zhou, R.; Ding, G.; Huang, S.; Dong, Y.; Lu, X. Toughening of epoxies by
covalently anchoring triazole-functionalized stacked-cup carbon nanofibers. Compos. Sci. Technol. 2013, 85,
1–9. [CrossRef]
Wang, R.; Li, Z.; Liu, W.; Jiao, W.; Hao, L.; Yang, F. Attapulgite–graphene oxide hybrids as thermal and
mechanical reinforcements for epoxy composites. Compos. Sci. Technol. 2013, 87, 29–35. [CrossRef]
Alishahi, E.; Shadlou, S.; Doagou-R, S.; Ayatollahi, M.R. Effects of carbon nanoreinforcements of different
shapes on the mechanical properties of epoxy-based nanocomposites. Macromol. Mater. Eng. 2013, 298,
670–678. [CrossRef]
Ma, J.; Meng, Q.; Michelmore, A.; Kawashima, N.; Izzuddin, Z.; Bengtsson, C.; Kuan, H.-C. Covalently
bonded interfaces for polymer/graphene composites. J. Mater. Chem. A 2013. [CrossRef]
Feng, H.; Wang, X.; Wu, D. Fabrication of spirocyclic phosphazene epoxy-based nanocomposites with
graphene via exfoliation of graphite platelets and thermal curing for enhancement of mechanical and
conductive properties. Ind. Eng. Chem. Res. 2013, 52, 10160–10171. [CrossRef]
Chatterjee, S.; Nafezarefi, F.; Tai, N.H.; Schlagenhauf, L.; Nüesch, F.A.; Chu, B.T.T. Size and synergy effects
of nanofiller hybrids including graphene nanoplatelets and carbon nanotubes in mechanical properties of
epoxy composites. Carbon 2012, 50, 5380–5386. [CrossRef]
Chatterjee, S.; Wang, J.W.; Kuo, W.S.; Tai, N.H.; Salzmann, C.; Li, W.L.; Hollertz, R.; Nüesch, F.A.; Chu, B.T.T.
Mechanical reinforcement and thermal conductivity in expanded graphene nanoplatelets reinforced epoxy
composites. Chem. Phys. Lett. 2012, 531, 6–10. [CrossRef]
Zaman, I.; Phan, T.T.; Kuan, H.-C.; Meng, Q.; Bao La, L.T.; Luong, L.; Youssf, O.; Ma, J. Epoxy/graphene
platelets nanocomposites with two levels of interface strength. Polymer (Guildf) 2011, 52, 1603–1611.
[CrossRef]
Rana, S.; Alagirusamy, R.; Joshi, M. Development of carbon nanofibre incorporated three phase carbon/epoxy
composites with enhanced mechanical, electrical and thermal properties. Compos. Part. A Appl. Sci. Manuf.
2011, 42, 439–445. [CrossRef]
Bortz, D.R.; Merino, C.; Martin-Gullon, I. Carbon nanofibers enhance the fracture toughness and fatigue
performance of a structural epoxy system. Compos. Sci. Technol. 2011, 71, 31–38. [CrossRef]
Zhang, G.; Karger-Kocsis, J.; Zou, J. Synergetic effect of carbon nanofibers and short carbon fibers on the
mechanical and fracture properties of epoxy resin. Carbon 2010, 48, 4289–4300. [CrossRef]
Fang, M.; Zhang, Z.; Li, J.; Zhang, H.; Lu, H.; Yang, Y. Constructing hierarchically structured interphases for
strong and tough epoxy nanocomposites by amine-rich graphene surfaces. J. Mater. Chem. 2010. [CrossRef]
Jana, S.; Zhong, W.-H. Graphite particles with a “puffed” structure and enhancement in mechanical
performance of their epoxy composites. Mater. Sci. Eng. A 2009, 525, 138–146. [CrossRef]
Rafiee, M.A.; Rafiee, J.; Srivastava, I.; Wang, Z.; Song, H.; Yu, Z.-Z.; Koratkar, N. Fracture and fatigue in
graphene nanocomposites. Small 2010, 6, 179–183. [CrossRef] [PubMed]
Kuhn, H.; Medlin, D. ASM Handbook, Volume 8: Mechanical Testing and Evaluation; ASM International:
Materials Park, OH, USA, 2000.
Griffith, A.A. The Phenomena of rupture and flow in solids. Philos. Trans. R. Soc. Lond. Ser. A Contain. Pap.
Math. Phys. Character 1921, 221, 163–198. [CrossRef]
Polymers 2016, 8, 281
93.
94.
95.
96.
97.
98.
99.
100.
101.
102.
103.
104.
105.
106.
107.
108.
109.
110.
111.
112.
113.
114.
115.
116.
117.
30 of 37
Zhang, W.; Srivastava, I.; Zhu, Y.F.; Picu, C.R.; Koratkar, N.A. Heterogeneity in epoxy nanocomposites
initiates crazing: Significant improvements in fatigue resistance and toughening. Small 2009, 5, 1403–1407.
[CrossRef] [PubMed]
ASM Handbook Volume 19: Fatigue and Fracture; ASM International: Materials Park, OH, USA, 1996.
Saharudin, M.S.; Atif, R.; Shyha, I.; Inam, F. The degradation of mechanical properties in polymer
nano-composites exposed to liquid media—A review. RSC Adv. 2016, 6, 1076–1089. [CrossRef]
Atif, R.; Shyha, I.; Inam, F. The degradation of mechanical properties due to stress concentration caused by
retained acetone in epoxy nanocomposites. RSC Adv. 2016, 6, 34188–34197. [CrossRef]
Chen, Q.; Liu, W.; Guo, S.; Zhu, S.; Li, Q.; Li, X.; et al. Synthesis of well-aligned millimeter-sized
tetragon-shaped graphene domains by tuning the copper substrate orientation. Carbon 2015, 93, 945–952.
[CrossRef]
Bhushan, B. Springer Handbook of Nanotechnology, 3rd ed.; Springer: Berlin, Germany, 2010.
Faber, K.T.; Evans, A.G. Crack deflection processes—I. Theory. Acta Metall. 1983, 31, 565–576. [CrossRef]
Faber, K.T.; Evans, A.G. Crack deflection processes—II. Experiment. Acta Metall. 1983, 31, 577–584. [CrossRef]
Xie, F. A facile strategy for the reduction of graphene oxide and its effect on thermal conductivity of
epoxy-based composites. Express Polym. Lett. 2016, 10, 470–478. [CrossRef]
Atif, R.; Inam, F. The dissimilarities between graphene and frame-like structures. Graphene 2016, 1, 55–72.
[CrossRef]
Fan, B.-B.; Guo, H.-H.; Zhang, R.; Jia, Y.; Shi, C.-Y. Structural evolution during the oxidation process of
graphite. Chin. Phys. Lett. 2014. [CrossRef]
Xu, Z.; Xue, K. Engineering graphene by oxidation: A first-principles study. Nanotechnology 2010. [CrossRef]
[PubMed]
Kuo, W.-S.; Tai, N.-H.; Chang, T.-W. Deformation and fracture in graphene nanosheets. Compos. Part A Appl.
Sci. Manuf. 2013, 51, 56–61. [CrossRef]
Palmeri, M.J.; Putz, K.W.; Brinson, L.C. Sacrificial bonds in stacked-cup carbon nanofibers: Biomimetic
toughening mechanisms for composite systems. ACS Nano 2010, 4, 4256–4264. [CrossRef] [PubMed]
Lee, D.; Zou, X.; Zhu, X.; Seo, J.W.; Cole, J.M.; Bondino, F.; Magnano, E.; Nair, S. K.; Su, H. Ultrafast carrier
phonon dynamics in NaOH-reacted graphite oxide film. Appl. Phys. Lett. 2012. [CrossRef]
Shojaee, S.A.; Zandiatashbar, A.; Koratkar, N.; Lucca, D.A. Raman spectroscopic imaging of graphene
dispersion in polymer composites. Carbon 2013, 62, 510–513. [CrossRef]
Tamburrano, A.; Sarasini, F.; de Bellis, G.; D’Aloia, A.G.; Sarto, M.S. The piezoresistive effect in
graphene-based polymeric composites. Nanotechnology 2013. [CrossRef] [PubMed]
Yang, H.; Li, F.; Shan, C.; Han, D.; Zhang, Q.; Niu, L.; Ivaska, A. Covalent functionalization of chemically
converted graphene sheets via silane and its reinforcement. J. Mater. Chem. 2009, 19, 4632–4638. [CrossRef]
Wang, G.; Shen, X.; Wang, B.; Yao, J.; Park, J. Synthesis and characterisation of hydrophilic and organophilic
graphene nanosheets. Carbon 2009, 47, 1359–1364. [CrossRef]
Samanman, S.; Numnuam, A.; Limbut, W.; Kanatharana, P.; Thavarungkul, P. Highly-sensitive label-free
electrochemical carcinoembryonic antigen immunosensor based on a novel Au nanoparticles–graphene–
chitosan nanocomposite cryogel electrode. Anal. Chim. Acta 2015, 853, 521–532. [CrossRef] [PubMed]
Lee, S.-Y.; Chong, M.-H.; Park, M.; Kim, H.-Y.; Park, S.-J. Effect of chemically reduced graphene oxide on
epoxy nanocomposites for flexural behaviors. Carbon Lett. 2014, 15, 67–70. [CrossRef]
Teng, C.-C.; Ma, C.-C.M.; Lu, C.-H.; Yang, S.-Y.; Lee, S.-H.; Hsiao, M.-C.; Yen, M.-Y.; Chiou, K.-C.; Lee, T.-M.
Thermal conductivity and structure of non-covalent functionalized graphene/epoxy composites. Carbon
2011, 49, 5107–5116. [CrossRef]
Chu, K.; Li, W.; Dong, H.; Tang, F. Modeling the thermal conductivity of graphene nanoplatelets reinforced
composites. EPL Europhys. Lett. 2012, 100, 36001–36005. [CrossRef]
Yang, S.-Y.; Lin, W.-N.; Huang, Y.-L.; Tien, H.-W.; Wang, J.-Y.; Ma, C.-C.M.; Li, S.-M.; Wang, Y.-S. Synergetic
effects of graphene platelets and carbon nanotubes on the mechanical and thermal properties of epoxy
composites. Carbon 2011, 49, 793–803. [CrossRef]
Pu, N.-W.; Peng, Y.-Y.; Wang, P.-C.; Chen, C.-Y.; Shi, J.-N.; Liu, Y.-M.; Ger, M.-D.; Chang, C.-L. Application
of nitrogen-doped graphene nanosheets in electrically conductive adhesives. Carbon 2014, 67, 449–456.
[CrossRef]
Polymers 2016, 8, 281
31 of 37
118. Zhao, Q.; Hao, S. Toughening mechanism of epoxy resins with micro/nano particles. J. Compos. Mater. 2007,
41, 201–219. [CrossRef]
119. Zhao, Q.; Hoa, S.; Ouellette, P. Progressive failure of triaxial woven fabric (TWF) composites with open holes.
Compos. Struct. 2004, 65, 419–431. [CrossRef]
120. Bastwros, M.; Kim, G.-Y.; Zhu, C.; Zhang, K.; Wang, S.; Tang, X.; Wang, X. Effect of ball milling on graphene
reinforced Al6061 composite fabricated by semi-solid sintering. Compos. Part B 2014, 60, 111–118. [CrossRef]
121. Wu, H.; Rook, B.; Drzal, L.T. Dispersion optimization of exfoliated graphene nanoplatelet in polyetherimide
nanocomposites: Extrusion, precoating, and solid state ball milling. Polym. Compos. 2013, 34, 426–432.
[CrossRef]
122. Yu, M.; Shao, D.; Lu, F.; Sun, X.; Sun, H.; Hu, T.; Wang, G.; Sawyer, S.; Qiu, H.; Lian, J. ZnO/graphene
nanocomposite fabricated by high energy ball milling with greatly enhanced lithium storage capability.
Electrochem. Commun. 2013, 34, 312–315. [CrossRef]
123. Jiang, X.; Drzal, L.T. Reduction in percolation threshold of injection molded high-density
polyethylene/exfoliated graphene nanoplatelets composites by solid state ball milling and solid state
shear pulverization. J. Appl. Polym. Sci. 2011, 124, 525–535. [CrossRef]
124. Wu, H.; Zhao, W.; Chen, G. One-pot in situ ball milling preparation of polymer/graphene nanocomposites.
J. Appl. Polym. Sci. 2012, 125, 3899–3903. [CrossRef]
125. Xu, J.; Jeon, I.-Y.; Seo, J.-M.; Dou, S.; Dai, L.; Baek, J.-B. Edge-selectively halogenated graphene nanoplatelets
(XGnPs, X = Cl, Br, or I) prepared by ball-milling and used as anode materials for lithium-ion batteries.
Adv. Mater. 2014, 26, 7317–7323. [CrossRef] [PubMed]
126. Guo, W.; Chen, G. Fabrication of graphene/epoxy resin composites with much enhanced thermal
conductivity via ball milling technique. J. Appl. Polym. Sci. 2014, 131, 40565–40569. [CrossRef]
127. Rodriguez, A.M.; Prieto, P.; Prato, M.; Va, E. Exfoliation of graphite with triazine derivatives under
ball-milling conditions: Preparation of few-layer graphene via selective noncovalent interactions. ACS Nano
2014, 8, 563–571.
128. Xu, J.; Shui, J.; Wang, J.; Wang, M.; Liu, H.; Dou, S.X.; Jeon, I. Sulfur–graphene nanostructured cathodes
via ball-milling for high-performance lithium–sulfur batteries. ACS Nano 2014, 8, 10920–10930. [CrossRef]
[PubMed]
129. Cravotto, G.; Cintas, P. Sonication-assisted fabrication and post-synthetic modifications of graphene-like
materials. Chemistry 2010, 16, 5246–5259. [CrossRef] [PubMed]
130. Yi, M.; Shen, Z.; Zhang, X.; Ma, S. Vessel diameter and liquid height dependent sonication-assisted production
of few-layer graphene. J. Mater. Sci. 2012, 47, 8234–8244. [CrossRef]
131. Ciesielski, A.; Samorì, P. Graphene via sonication assisted liquid-phase exfoliation. Chem. Soc. Rev. 2014, 43,
381–398. [CrossRef] [PubMed]
132. Wang, S.; Tang, L.A.L.; Bao, Q.; Lin, M.; Deng, S.; Goh, B.M.; Loh, K. P. Room-temperature synthesis of
soluble carbon nanotubes by the sonication of graphene oxide nanosheets. J. Am. Chem. Soc. 2009, 131,
16832–16837. [CrossRef] [PubMed]
133. Akhavan, O.; Ghaderi, E.; Esfandiar, A. Wrapping bacteria by graphene nanosheets for isolation from
environment, reactivation by sonication, and inactivation by near-infrared irradiation. J. Phys. Chem. B 2011,
115, 6279–6288. [CrossRef] [PubMed]
134. Polyakova Stolyarova, E.Y.; Rim, K.T.; Eom, D.; Douglass, K.; Opila, R.L.; Heinz, T.F.; Teplyakov, A.V.;
Flynn, G.W. Scanning tunneling microscopy and X-ray photoelectron spectroscopy studies of graphene films
prepared by sonication-assisted dispersion. ACS Nano 2011, 5, 6102–6108. [CrossRef] [PubMed]
135. Xu, P.; Loomis, J.; King, B.; Panchapakesan, B. Synergy among binary (MWNT, SLG) nano-carbons in polymer
nano-composites: A Raman study. Nanotechnology 2012. [CrossRef] [PubMed]
136. Cheng, Y.C.; Kaloni, T.P.; Zhu, Z.Y.; Schwingenschlögl, U. Oxidation of graphene in ozone under ultraviolet
light. Appl. Phys. Lett. 2012. [CrossRef]
137. Gracia-espino, E.; Hu, G.; Shchukarev, A.; Wa, T. Understanding the interface of six-shell cuboctahedral
and icosahedral palladium clusters on reduced graphene oxide: Experimental and theoretical study. J. Am.
Chem. Soc. 2014, 136, 6626–6633. [CrossRef] [PubMed]
138. Velizhanin, K.A.; Dandu, N.; Solenov, D. Electromigration of bivalent functional groups on graphene.
Phys. Rev. B 2014. [CrossRef]
Polymers 2016, 8, 281
32 of 37
139. Radovic, L.R.; Suarez, A.; Vallejos-Burgos, F.; Sofo, J.O. Oxygen migration on the graphene surface.
2. Thermochemistry of basal-plane diffusion (hopping). Carbon 2011, 49, 4226–4238. [CrossRef]
140. Radovic, L.R.; Silva-Tapia, A.B.; Vallejos-Burgos, F. Oxygen migration on the graphene surface. 1. Origin of
epoxide groups. Carbon 2011, 49, 4218–4225. [CrossRef]
141. Botas, C.; Álvarez, P.; Blanco, C.; Santamaría, R.; Granda, M.; Ares, P.; Rodríguez-Reinoso, F.; Menéndez, R.
The effect of the parent graphite on the structure of graphene oxide. Carbon 2012, 50, 275–282. [CrossRef]
142. Šljivančanin, Ž.; Milošević, A.S.; Popović, Z.S.; Vukajlović, F.R. Binding of atomic oxygen on graphene from
small epoxy clusters to a fully oxidized surface. Carbon 2013, 54, 482–488. [CrossRef]
143. Ahmed, M.S.; Han, H.S.; Jeon, S. One-step chemical reduction of graphene oxide with oligothiophene for
improved electrocatalytic oxygen reduction reactions. Carbon 2013, 61, 164–172. [CrossRef]
144. Yuan, F.-Y.; Zhang, H.-B.; Li, X.; Ma, H.-L.; Li, X.-Z.; Yu, Z.-Z. In situ chemical reduction and functionalization
of graphene oxide for electrically conductive phenol formaldehyde composites. Carbon 2014, 68, 653–661.
[CrossRef]
145. Jiang, X.; Nisar, J.; Pathak, B.; Zhao, J.; Ahuja, R. Graphene oxide as a chemically tunable 2-D material for
visible-light photocatalyst applications. J. Catal. 2013, 299, 204–209. [CrossRef]
146. Park, J.S.; Yu, L.; Lee, C.S.; Shin, K.; Han, J.H. Liquid-phase exfoliation of expanded graphites into graphene
nanoplatelets using amphiphilic organic molecules. J. Colloid Interface Sci. 2014, 417, 379–384. [CrossRef]
[PubMed]
147. Karger-Kocsis, J.; Friedrich, K. Microstructure-related fracture toughness and fatigue crack growth behaviour
in toughened, anhydride-cured epoxy resins. Compos. Sci. Technol. 1993, 48, 263–272. [CrossRef]
148. Karger-Kocsis, J.; Gremmels, J. Use of hygrothermal decomposed polyester–urethane waste for the impact
modification of epoxy resins. J. Appl. Polym. Sci. 2000, 5, 1139–1151. [CrossRef]
149. Smith, G.; Bedrov, D.; Li, L.; Byutner, O. A molecular dynamics simulation study of the viscoelastic properties
of polymer nanocomposites. J. Chem. Phys. 2002, 117, 9478–9489. [CrossRef]
150. Corcione, C.E.; Freuli, F.; Maffezzoli, A. The aspect ratio of epoxy matrix nanocomposites reinforced with
graphene stacks. Polym. Eng. Sci. 2013, 53, 531–539. [CrossRef]
151. Ramos-Galicia, L.; Mendez, L.N.; Martínez-Hernández, A.L.; Espindola-Gonzalez, A.; Galindo-Esquivel, I.R.;
Fuentes-Ramirez, R.; Velasco-Santos, C. Improved performance of an epoxy matrix as a result of combining
graphene oxide and reduced graphene. Int. J. Polym. Sci. 2013, 2013, 1–7. [CrossRef]
152. Li, Z.; Young, R.J.; Wang, R.; Yang, F.; Hao, L.; Jiao, W.; Liu, W. The role of functional groups on graphene
oxide in epoxy nanocomposites. Polymer (Guildf) 2013, 54, 5821–5829. [CrossRef]
153. Liu, W.; Koh, K.L.; Lu, J.; Yang, L.; Phua, S.; Kong, J.; Chen, Z.; Lu, X. Simultaneous catalyzing and reinforcing
effects of imidazole-functionalized graphene in anhydride-cured epoxies. J. Mater. Chem. 2012. [CrossRef]
154. Yang, H.; Shan, C.; Li, F.; Zhang, Q.; Han, D.; Niu, L. Convenient preparation of tunably loaded chemically
converted graphene oxide/epoxy resin nanocomposites from graphene oxide sheets through two-phase
extraction. J. Mater. Chem. 2009, 19, 8856. [CrossRef]
155. Galpaya, D.; Wang, M.; George, G.; Motta, N.; Waclawik, E.; Yan, C. Preparation of graphene oxide/epoxy
nanocomposites with significantly improved mechanical properties. J. Appl. Phys. 2014. [CrossRef]
156. Li, W.; Dichiara, A.; Bai, J. Carbon nanotube–graphene nanoplatelet hybrids as high-performance
multifunctional reinforcements in epoxy composites. Compos. Sci. Technol. 2013, 74, 221–227. [CrossRef]
157. Cao, L.; Liu, X.; Na, H.; Wu, Y.; Zheng, W.; Zhu, J. How a bio-based epoxy monomer enhanced the properties
of diglycidyl ether of bisphenol A (DGEBA)/graphene composites. J. Mater. Chem. A 2013, 1, 5081–5088.
[CrossRef]
158. Wan, Y.-J.; Tang, L.-C.; Yan, D.; Zhao, L.; Li, Y.-B.; Wu, L.-B.; Jiang, J.-X.; Lai, G.-Q. Improved dispersion and
interface in the graphene/epoxy composites via a facile surfactant-assisted process. Compos. Sci. Technol.
2013, 82, 60–68. [CrossRef]
159. Ghaleb, Z.A.; Mariatti, M.; Ariff, Z.M. Properties of graphene nanopowder and multi-walled carbon
nanotube-filled epoxy thin-film nanocomposites for electronic applications: The effect of sonication time and
filler loading. Compos. Part A 2014, 58, 77–83. [CrossRef]
160. King, J.A.; Klimek, D.R.; Miskioglu, I.; Odegard, G.M. Mechanical properties of graphene nanoplatelet/epoxy
composites. J. Appl. Polym. Sci. 2013, 128, 4217–4223. [CrossRef]
Polymers 2016, 8, 281
33 of 37
161. Wang, X.; Song, L.; Pornwannchai, W.; Hu, Y.; Kandola, B. The effect of graphene presence in flame retarded
epoxy resin matrix on the mechanical and flammability properties of glass fiber-reinforced composites.
Compos. Part A 2013, 53, 88–96. [CrossRef]
162. Serena Saw, W.P.; Mariatti, M. Properties of synthetic diamond and graphene nanoplatelet-filled epoxy thin
film composites for electronic applications. J. Mater. Sci. Mater. Electron. 2011, 23, 817–824. [CrossRef]
163. Zaman, I.; Kuan, H.-C.; Meng, Q.; Michelmore, A.; Kawashima, N.; Pitt, T.; Zhang, L.; Gouda, S.;
Luong, L.; Ma, J. A Facile Approach to Chemically Modified Graphene and its Polymer Nanocomposites.
Adv. Funct. Mater. 2012, 22, 2735–2743. [CrossRef]
164. Hsu, C.-H.; Hsu, M.-H.; Chang, K.-C.; Lai, M.-C.; Liu, P.-J.; Chuang, T.-L.; Yeh, J.-M.; Liu, W.-R. Physical
study of room-temperature-cured epoxy/thermally reduced graphene oxides with various contents of
oxygen-containing groups. Polym. Int. 2014, 63, 1765–1770. [CrossRef]
165. Yang, Y.; Rigdon, W.; Huang, X.; Li, X. Enhancing graphene reinforcing potential in composites by hydrogen
passivation induced dispersion. Sci. Rep. 2013, 3, 2086–2093. [CrossRef] [PubMed]
166. Naebe, M.; Wang, J.; Amini, A.; Khayyam, H.; Hameed, N.; Li, L.H.; Chen, Y.; Fox, B. Mechanical property
and structure of covalent functionalised graphene/epoxy nanocomposites. Sci. Rep. 2014, 4, 4375–4382.
[CrossRef] [PubMed]
167. Qi, B.; Yuan, Z.; Lu, S.; Liu, K.; Li, S.; Yang, L.; Yu, J. Mechanical and thermal properties of epoxy composites
containing graphene oxide and liquid crystalline epoxy. Fibers Polym. 2014, 15, 326–333. [CrossRef]
168. Ren, F.; Zhu, G.; Ren, P.; Wang, Y.; Cui, X. In situ polymerization of graphene oxide and cyanate ester–epoxy
with enhanced mechanical and thermal properties. Appl. Surf. Sci. 2014, 316, 549–557. [CrossRef]
169. Qi, B. Enhanced thermal and mechanical properties of epoxy composites by mixing thermotropic liquid
crystalline epoxy grafted graphene oxide. Express Polym. Lett. 2014, 8, 467–479. [CrossRef]
170. Lu, S.; Li, S.; Yu, J.; Yuan, Z.; Qi, B. Epoxy nanocomposites filled with thermotropic liquid crystalline epoxy
grafted graphene oxide. RSC Adv. 2013, 3, 8915. [CrossRef]
171. Shen, X.-J.; Liu, Y.; Xiao, H.-M.; Feng, Q.-P.; Yu, Z.-Z.; Fu, S.-Y. The reinforcing effect of graphene nanosheets
on the cryogenic mechanical properties of epoxy resins. Compos. Sci. Technol. 2012, 72, 1581–1587. [CrossRef]
172. Bao, C.; Guo, Y.; Song, L.; Kan, Y.; Qian, X.; Hu, Y. In situ preparation of functionalized graphene oxide/epoxy
nanocomposites with effective reinforcements. J. Mater. Chem. 2011, 21, 13290–13298. [CrossRef]
173. Meng, Q.; Jin, J.; Wang, R.; Kuan, H.-C.; Ma, J.; Kawashima, N.; Michelmore, A.; Zhu, S.; Wang, C.H.
Processable 3-nm thick graphene platelets of high electrical conductivity and their epoxy composites.
Nanotechnology 2014, 25, 125707–125719. [CrossRef] [PubMed]
174. Atif, R.; Shyha, I.; Inam, F. Modeling and experimentation of multi-layered nanostructured graphene-epoxy
nanocomposites for enhanced thermal and mechanical properties. J. Compos. Mater. 2016. [CrossRef]
175. Yu, A.; Ramesh, P.; Itkis, M.E.; Bekyarova, E.; Haddon, R.C. Graphite nanoplatelet—epoxy composite thermal
interface materials. J. Phys. Chem. C 2007, 111, 7565–7569. [CrossRef]
176. Yavari, F.; Fard, H.R.; Pashayi, K.; Rafiee, M.a.; Zamiri, A.; Yu, Z.; Ozisik, R.; Borca-Tasciuc, T.; Koratkar, N.
Enhanced thermal conductivity in a nanostructured phase change composite due to low concentration
graphene additives. J. Phys. Chem. C 2011, 115, 8753–8758. [CrossRef]
177. Ganguli, S.; Roy, A.K.; Anderson, D.P. Improved thermal conductivity for chemically functionalized
exfoliated graphite/epoxy composites. Carbon 2008, 46, 806–817. [CrossRef]
178. Fukushima, H.; Drzal, L.T.; Rook, B.P.; Rich, M.J. Thermal conductivity of exfoliated graphite nanocomposites.
J. Therm. Anal. Calorim. 2006, 85, 235–238. [CrossRef]
179. Xie, S.H.; Liu, Y.Y.; Li, J.Y. Comparison of the effective conductivity between composites reinforced by
graphene nanosheets and carbon nanotubes. Appl. Phys. Lett. 2008, 92, 1–3. [CrossRef]
180. Lin, W.; Zhang, R.; Wong, C.P. Modeling of thermal conductivity of graphite nanosheet composites.
J. Electron. Mater. 2010, 39, 268–272. [CrossRef]
181. Nan, C.-W.; Birringer, R.; Clarke, D.R.; Gleiter, H. Effective thermal conductivity of particulate composites
with interfacial thermal resistance. J. Appl. Phys. 1997, 81, 6692–6699. [CrossRef]
182. Shiu, S.-C.; Tsai, J.-L. Characterizing thermal and mechanical properties of graphene/epoxy nanocomposites.
Compos. Part B 2014, 56, 691–697. [CrossRef]
183. Yu, G.; Wu, P. Effect of chemically modified graphene oxide on the phase separation behaviour and properties
of an epoxy/polyetherimide binary system. Polym. Chem. 2014, 5, 96–104. [CrossRef]
Polymers 2016, 8, 281
34 of 37
184. Liu, T.; Zhao, Z.; Tjiu, W.W.; Lv, J.; Wei, C. Preparation and characterization of epoxy nanocomposites
containing surface-modified graphene oxide. J. Appl. Polym. Sci. 2014, 131, 40236–40242. [CrossRef]
185. Liu, F.; Guo, K. Reinforcing epoxy resin through covalent integration of functionalized graphene nanosheets.
Polym. Adv. Technol. 2014, 25, 418–423. [CrossRef]
186. Guan, L.-Z.; Wan, Y.-J.; Gong, L.-X.; Yan, D.; Tang, L.-C.; Wu, L.-B.; Jiang, J.-X.; Lai, G.-Q. Toward
effective and tunable interphases in graphene oxide/epoxy composites by grafting different chain lengths of
polyetheramine onto graphene oxide. J. Mater. Chem. A 2014, 2, 15058–15069. [CrossRef]
187. Martin-Gallego, M.; Bernal, M.M.; Hernandez, M.; Verdejo, R.; Lopez-Manchado, M.A. Comparison of filler
percolation and mechanical properties in graphene and carbon nanotubes filled epoxy nanocomposites.
Eur. Polym. J. 2013, 49, 1347–1353. [CrossRef]
188. Ribeiro, H.; Silva, W.M.; Rodrigues, M.-T.F.; Neves, J.C.; Paniago, R.; Fantini, C.; Calado, H.D.R.; Seara, L.M.;
Silva, G.G. Glass transition improvement in epoxy/graphene composites. J. Mater. Sci. 2013, 48, 7883–7892.
[CrossRef]
189. Wajid, A.S.; Ahmed, H.S.T.; Das, S.; Irin, F.; Jankowski, A.F.; Green, M.J. High-Performance Pristine
Graphene/Epoxy Composites With Enhanced Mechanical and Electrical Properties. Macromol. Mater. Eng.
2013, 298, 339–347. [CrossRef]
190. Zhang, X.; Alloul, O.; He, Q.; Zhu, J.; Verde, M.J.; Li, Y.; Wei, S.; Guo, Z. Strengthened magnetic epoxy
nanocomposites with protruding nanoparticles on the graphene nanosheets. Polymer (Guildf) 2013, 54,
3594–3604. [CrossRef]
191. Wang, X.; Xing, W.; Feng, X.; Yu, B.; Song, L.; Hu, Y. Functionalization of graphene with grafted
polyphosphamide for flame retardant epoxy composites: Synthesis, flammability and mechanism.
Polym. Chem. 2014. [CrossRef]
192. Hu, L.; Desai, T.; Keblinski, P. Thermal transport in graphene-based nanocomposite. J. Appl. Phys. 2011, 110,
1–6. [CrossRef]
193. Li, Q.; Guo, Y.; Li, W.; Qiu, S.; Zhu, C.; Wei, X.; Chen, M.; Liu, C.; Liao, S.; Gong, Y.; Mishra, A. K.;
Liu, L. Ultrahigh Thermal Conductivity of Assembled Aligned Multilayer Graphene/Epoxy Composite.
Chem. Mater. 2014, 26, 4459–4465. [CrossRef]
194. Geim, A.K. Graphene: Status and Prospects. Science 2009, 324, 1530–1535. [CrossRef] [PubMed]
195. Geim, A.K.; Novoselov, K.S. The rise of graphene. Nat. Mater. 2007, 6, 183–191. [CrossRef] [PubMed]
196. Yan, W.; He, W.-Y.; Chu, Z.-D.; Liu, M.; Meng, L.; Dou, R.-F.; Zhang, Y.; Liu, Z.; Nie, J.-C.; He, L. Strain and
curvature induced evolution of electronic band structures in twisted graphene bilayer. Nat. Commun. 2013, 4,
1–7. [CrossRef] [PubMed]
197. Castro Neto, A.H.; Peres, N.M.R.; Novoselov, K.S.; Geim, A.K.; Guinea, F. The electronic properties of
graphene. Rev. Mod. Phys. 2009, 81, 109–162. [CrossRef]
198. Zhang, Y.; Tan, Y.-W.; Stormer, H. L.; Kim, P. Experimental observation of the quantum Hall effect and Berry’s
phase in graphene. Nature 2005, 438, 201–204. [CrossRef] [PubMed]
199. Novoselov, K.S.; Geim, A.K.; Morozov, S.V.; Jiang, D.; Katsnelson, M.I.; Grigorieva, I.V.; Dubonos, S.V.;
Firsov, A.A. Two-dimensional gas of massless Dirac fermions in graphene. Nature 2005, 438, 197–200.
[CrossRef] [PubMed]
200. Zhao, L.; Levendorf, M.; Goncher, S.; Schiros, T.; Pálová, L.; Zabet-Khosousi, A.; Rim, K. T.; Gutiérrez, C.;
Nordlund, D.; Jaye, C.; Hybertsen, M.; Reichman, D.; Flynn, G. W.; Park, J.; Pasupathy, A. N. Local atomic
and electronic structure of boron chemical doping in monolayer graphene. Nano Lett. 2013, 13, 4659–4665.
[CrossRef] [PubMed]
201. Han, W.; Kawakami, R.K.; Gmitra, M.; Fabian, J. Graphene spintronics. Nat. Nanotechnol. 2014, 9, 794–807.
[CrossRef] [PubMed]
202. Kandare, E.; Khatibi, A.A.; Yoo, S.; Wang, R.; Ma, J.; Olivier, P.; Gleizes, N.; Wang, C.H. Improving the
through-thickness thermal and electrical conductivity of carbon fibre/epoxy laminates by exploiting synergy
between graphene and silver nano-inclusions. Compos. Part A 2015, 69, 72–82. [CrossRef]
203. Tang, B.; Hu, G.; Gao, H.; Hai, L. Application of graphene as filler to improve thermal transport property of
epoxy resin for thermal interface materials. Int. J. Heat Mass Transf. 2015, 85, 420–429. [CrossRef]
204. Burger, N.; Laachachi, A.; Mortazavi, B.; Ferriol, M.; Lutz, M.; Toniazzo, V.; Ruch, D. Alignments and network
of graphite fillers to improve thermal conductivity of epoxy-based composites. Int. J. Heat Mass Transf. 2015,
89, 505–513. [CrossRef]
Polymers 2016, 8, 281
35 of 37
205. Zeng, C.; Lu, S.; Xiao, X.; Gao, J.; Pan, L.; He, Z.; Yu, J. Enhanced thermal and mechanical properties of
epoxy composites by mixing noncovalently functionalized graphene sheets. Polym. Bull. 2014, 72, 453–472.
[CrossRef]
206. Wang, F.; Drzal, L.T.; Qin, Y.; Huang, Z. Mechanical properties and thermal conductivity of graphene
nanoplatelet/epoxy composites. J. Mater. Sci. 2014, 50, 1082–1093. [CrossRef]
207. Zhou, T.; Nagao, S.; Sugahara, T.; Koga, H.; Nogi, M.; Suganuma, K.; Nge, T.T.; Nishina, Y. Facile identification
of the critical content of multi-layer graphene oxide for epoxy composite with optimal thermal properties.
RSC Adv. 2015, 5, 20376–20385. [CrossRef]
208. Zeng, C.; Lu, S.; Song, L.; Xiao, X.; Gao, J.; Pan, L.; He, Z.; Yu, J. Enhanced thermal properties in a hybrid
graphene–alumina filler for epoxy composites. RSC Adv. 2015, 5, 35773–35782. [CrossRef]
209. Tang, D.; Su, J.; Yang, Q.; Kong, M.; Zhao, Z.; Huang, Y.; Liao, X.; Liu, Y. Preparation of alumina-coated
graphite for thermally conductive and electrically insulating epoxy composites. RSC Adv. 2015, 5,
55170–55178. [CrossRef]
210. Pan, L.; Ban, J.; Lu, S.; Chen, G.; Yang, J.; Luo, Q.; Wu, L.; Yu, J. Improving thermal and mechanical properties
of epoxy composites by using functionalized graphene. RSC Adv. 2015, 5, 60596–60607. [CrossRef]
211. Wang, R.; Zhuo, D.; Weng, Z.; Wu, L.; Cheng, X.; Zhou, Y.; Wang, J.; Xuan, B. A novel nanosilica/graphene
oxide hybrid and its flame retarding epoxy resin with simultaneously improved mechanical, thermal
conductivity, and dielectric properties. J. Mater. Chem. A 2015, 3, 9826–9836. [CrossRef]
212. Zha, J.-W.; Zhu, T.-X.; Wu, Y.-H.; Wang, S.-J.; Li, R.K.Y.; Dang, Z.-M. Tuning of thermal and dielectric
properties for epoxy composites filled with electrospun alumina fibers and graphene nanoplatelets through
hybridization. J. Mater. Chem. C 2015, 3, 7195–7202. [CrossRef]
213. Zhou, T. Targeted kinetic strategy for improving the thermal conductivity of epoxy composite containing
percolating multi-layer graphene oxide chains. Express Polym. Lett. 2015, 9, 608–623. [CrossRef]
214. Wang, Y.; Yu, J.; Dai, W.; Song, Y.; Wang, D.; Zeng, L.; Jiang, N. Enhanced Thermal and Electrical Properties
of Epoxy Composites Reinforced With Graphene Nanoplatelets. Polym. Compos. 2015. [CrossRef]
215. Pu, X.; Zhang, H.-B.; Li, X.; Gui, C.; Yu, Z.-Z. Thermally conductive and electrically insulating epoxy
nanocomposites with silica-coated graphene. RSC Adv. 2014, 4, 15297–15303. [CrossRef]
216. Fu, Y.-X.; He, Z.-X.; Mo, D.-C.; Lu, S.-S. Thermal conductivity enhancement of epoxy adhesive using graphene
sheets as additives. Int. J. Therm. Sci. 2014, 86, 276–283. [CrossRef]
217. Esposito Corcione, C.; Maffezzoli, A. Transport properties of graphite/epoxy composites: Thermal,
permeability and dielectric characterization. Polym. Test. 2013, 32, 880–888. [CrossRef]
218. Min, C.; Yu, D.; Cao, J.; Wang, G.; Feng, L. A graphite nanoplatelet/epoxy composite with high dielectric
constant and high thermal conductivity. Carbon 2013, 55, 116–125. [CrossRef]
219. Hsiao, M.-C.; Ma, C.-C.M.; Chiang, J.-C.; Ho, K.-K.; Chou, T.-Y.; Xie, X.; et al. Thermally conductive
and electrically insulating epoxy nanocomposites with thermally reduced graphene oxide-silica hybrid
nanosheets. Nanoscale 2013, 5, 5863–5871. [CrossRef] [PubMed]
220. Zhou, T.; Wang, X.; Cheng, P.; Wang, T.; Xiong, D.; Wang, X. Improving the thermal conductivity of
epoxy resin by the addition of a mixture of graphite nanoplatelets and silicon carbide microparticles.
Express Polym. Lett. 2013, 7, 585–594. [CrossRef]
221. Raza, M.A.; Westwood, A.V.K.; Stirling, C. Effect of processing technique on the transport and
mechanical properties of graphite nanoplatelet/rubbery epoxy composites for thermal interface applications.
Mater. Chem. Phys. 2012, 132, 63–73. [CrossRef]
222. Kim, J.; Yim, B.; Kim, J.; Kim, J. The effects of functionalized graphene nanosheets on the thermal and
mechanical properties of epoxy composites for anisotropic conductive adhesives (ACAs). Microelectron. Reliab.
2012, 52, 595–602. [CrossRef]
223. Im, H.; Kim, J. Thermal conductivity of a graphene oxide–carbon nanotube hybrid/epoxy composite. Carbon
2012, 50, 5429–5440. [CrossRef]
224. Heo, Y.; Im, H.; Kim, J.; Kim, J. The influence of Al(OH)3 -coated graphene oxide on improved thermal
conductivity and maintained electrical resistivity of Al2 O3 /epoxy composites. J. Nanopart. Res. 2012, 14,
1–10. [CrossRef]
225. Huang, X.; Zhi, C.; Jiang, P. Toward Effective Synergetic Effects from Graphene Nanoplatelets and Carbon
Nanotubes on Thermal Conductivity of Ultrahigh Volume Fraction Nanocarbon Epoxy Composites. J. Phys.
Chem. C 2012, 116, 23812–23820. [CrossRef]
Polymers 2016, 8, 281
36 of 37
226. Martin-gallego, M.; Verdejo, R.; Khayet, M.; Maria, J.; De Zarate, O.; Essalhi, M.; Lopez-manchado, M.A.
Thermal conductivity of carbon nanotubes and graphene in epoxy nanofluids and nanocomposites.
Nanoscale Res. Lett. 2011, 6, 1–7. [CrossRef] [PubMed]
227. Tien, D.H.; Joonkyu, P.; Sang, A.H.; Muneer, A.; Yongho, S.; Koo, S. Electrical and Thermal Conductivities of
Stycast 1266 Epoxy/Graphite Composites. J. Korean Phys. Soc. 2011, 59, 2760–2764.
228. Yu, A.; Ramesh, P.; Sun, X.; Bekyarova, E.; Itkis, M.E.; Haddon, R.C. Enhanced thermal conductivity in a
hybrid graphite nanoplatelet—Carbon nanotube filler for epoxy composites. Adv. Mater. 2008, 20, 4740–4744.
[CrossRef]
229. Wu, S.; Ladani, R.B.; Zhang, J.; Bafekrpour, E.; Ghorbani, K.; Mouritz, A.P.; Kinloch, A.J.; Wang, C.H. Aligning
multilayer graphene flakes with an external electric field to improve multifunctional properties of epoxy
nanocomposites. Carbon 2015, 94, 607–618. [CrossRef]
230. Liu, X.; Sun, X.; Wang, Z.; Shen, X.; Wu, Y.; Kim, J.-K. Planar Porous Graphene Woven Fabric/Epoxy
Composites with Exceptional Electrical, Mechanical Properties, and Fracture Toughness. ACS Appl.
Mater. Interfaces 2015, 7, 21455–21464. [CrossRef] [PubMed]
231. Ming, P.; Zhang, Y.; Bao, J.; Liu, G.; Li, Z.; Jiang, L.; Cheng, Q. Bioinspired highly electrically conductive
graphene–epoxy layered composites. RSC Adv. 2015, 5, 22283–22288. [CrossRef]
232. Tang, G.; Jiang, Z.-G.; Li, X.; Zhang, H.-B.; Hong, S.; Yu, Z.-Z. Electrically conductive
rubbery epoxy/diamine-functionalized graphene nanocomposites with improved mechanical properties.
Compos. Part B Eng. 2014, 67, 564–570. [CrossRef]
233. Dou, S.; Qi, J.; Guo, X.; Yu, C. Preparation and adhesive performance of electrical conductive epoxy-acrylate
resin containing silver-plated graphene. J. Adhes Sci. Technol. 2014, 28, 1556–1567. [CrossRef]
234. Tang, G.; Jiang, Z.-G.; Li, X.; Zhang, H.-B.; Yu, Z.-Z. Simultaneous functionalization and reduction of graphene
oxide with polyetheramine and its electrically conductive epoxy nanocomposites. Chin. J. Polym. Sci. 2014,
32, 975–985. [CrossRef]
235. Monti, M.; Rallini, M.; Puglia, D.; Peponi, L.; Torre, L.; Kenny, J.M. Morphology and electrical properties of
graphene–epoxy nanocomposites obtained by different solvent assisted processing methods. Compos. Part A
Appl. Sci. Manuf. 2013, 46, 166–172. [CrossRef]
236. Suherman, H.; Sulong, A.B.; Sahari, J. Effect of the compression molding parameters on the in-plane and
through-plane conductivity of carbon nanotubes/graphite/epoxy nanocomposites as bipolar plate material
for a polymer electrolyte membrane fuel cell. Ceram. Int. 2013, 39, 1277–1284. [CrossRef]
237. Mancinelli, P.; Heid, T.F.; Fabiani, D.; Saccani, A.; Toselli, M.; Frechette, M.F.; Savoie, S.; David, E. Electrical
conductivity of graphene-based epoxy nanodielectrics. In Proceedings of the 2013 Annual Report Conference
on Electrical Insulation and Dielectric Phenomena, Shenzhen, China, 20–23 October 2013; pp. 772–775.
238. Al-Ghamdi, A.A.; Al-Hartomy, O.A.; Al-Solamy, F.; Al-Ghamdi, A.A.; El-Tantawy, F. Electromagnetic wave
shielding and microwave absorbing properties of hybrid epoxy resin/foliated graphite nanocomposites.
J. Appl. Polym. Sci. 2013, 127, 2227–2234. [CrossRef]
239. Kim, J.; Im, H.; Kim, J.; Kim, J. Thermal and electrical conductivity of Al(OH)3 covered graphene oxide
nanosheet/epoxy composites. J. Mater. Sci. 2011, 47, 1418–1426. [CrossRef]
240. Fan, Z.; Zheng, C.; Wei, T.; Zhang, Y.; Lu, G. Effect of Carbon Black on Electrical Property of Graphite
Nanoplatelets/Epoxy Resin Composites. Polym. Eng. Sci. 2009, 49, 2041–2045. [CrossRef]
241. Jović, N.; Dudić, D.; Montone, A.; Antisari, M.V.; Mitrić, M.; Djoković, V. Temperature dependence of the
electrical conductivity of epoxy/expanded graphite nanosheet composites. Scr. Mater. 2008, 58, 846–849.
[CrossRef]
242. Li, J.; Ma, P.C.; Chow, W.S.; To, C.K.; Tang, B.Z.; Kim, J.-K. Correlations between Percolation Threshold,
Dispersion State, and Aspect Ratio of Carbon Nanotubes. Adv. Funct. Mater. 2007, 17, 3207–3215. [CrossRef]
243. Sandler, J.; Shaffer, M.S.; Prasse, T.; Bauhofer, W.; Schulte, K.; Windle, A. Development of a dispersion process
for carbon nanotubes in an epoxy matrix and the resulting electrical properties. Polymer (Guildf) 1999, 40,
5967–5971. [CrossRef]
244. Raza, M.A.; Westwood, A.; Stirling, C. Effect of processing technique on the transport and mechanical
properties of vapour grown carbon nanofibre/rubbery epoxy composites for electronic packaging
applications. Carbon 2012, 50, 84–97. [CrossRef]
245. Mas, B.; Fernández-Blázquez, J.P.; Duval, J.; Bunyan, H.; Vilatela, J.J. Thermoset curing through Joule heating
of nanocarbons for composite manufacture, repair and soldering. Carbon 2013, 63, 523–529. [CrossRef]
Polymers 2016, 8, 281
37 of 37
246. Chang, K.-C.; Hsu, M.-H.; Lu, H.-I.; Lai, M.-C.; Liu, P.-J.; Hsu, C.-H.; Ji, W.-F.; Chuang, T.-L.; Wei, Y.; Yeh, J.-M.;
Liu, W.-R. Room-temperature cured hydrophobic epoxy/graphene composites as corrosion inhibitor for
cold-rolled steel. Carbon 2014, 66, 144–153. [CrossRef]
247. Prolongo, S.G.; Jiménez-Suárez, A.; Moriche, R.; Ureña, A. Graphene nanoplatelets thickness and lateral size
influence on the morphology and behavior of epoxy composites. Eur. Polym. J. 2014, 53, 292–301. [CrossRef]
248. Prolongo, S.G.; Moriche, R.; Jiménez-Suárez, A.; Sanchez, M.; Ureña, A. Advantages and disadvantages of
the addition of graphene nanoplatelets to epoxy resins. Eur. Polym. J. 2014, 61, 206–214. [CrossRef]
© 2016 by the authors; licensee MDPI, Basel, Switzerland. This article is an open access
article distributed under the terms and conditions of the Creative Commons Attribution
(CC-BY) license (http://creativecommons.org/licenses/by/4.0/).
Was this manual useful for you? yes no
Thank you for your participation!

* Your assessment is very important for improving the work of artificial intelligence, which forms the content of this project

Download PDF

advertisement