60 Adv. Mater. Sci. 40 (2015) 60-71
Rev.
J.-F. Dai, G.-J. Wang, L. Ma and Ch.-K. Wu
SURFACE PROPERTIES OF GRAPHENE: RELATIONSHIP
TO GRAPHENE-POLYMER COMPOSITES
Jin-Feng Dai1, Guo-Jian Wang1,2, Lang Ma1 and Cheng-Ken Wu1
1
2
School of Materials Science and Engineering, Tongji University, Shanghai 201804, China
Key Laboratory of Advanced Civil Engineering Materials, Ministry of Education, Shanghai 201804, China
Received: October 23, 2014
Abstract. Graphene has attracted much attention in recent years due to its extraordinary electronic, optical, magnetic, thermal, and mechanical properties. Despite continuing theoretical and
experimental success, the unique physical properties of graphene remain underused and
underappreciated. The key challenge in harnessing of the unique properties of graphene is the
difficulty of reliable manipulation of well-dispersed graphene which due to the surface properties
of graphene. In this review, the recent developments of surface properties of graphene are
summarized, where tailoring of these surface properties via surface treatments and the effects
on the graphene-polymer matrix interface is highlighted. Moreover, the surface testing technique
is also commented on briefly. We believe that the future prospects of research emphasis on
preparation of modified graphene with special surface properties which would lead to better
composites taking into account the desired cradle-to-grave lifecycle of reinforced materials with
high performance. Finally, we expect that this review can contribute to a better knowledge of the
physicochemical surface properties of graphene.
1. INTRODUCTION
[13], and organic synthesis [14]. The advances in
preparation of graphene [2] not only provide commercial access to lager-area samples, but also further promote the application of graphene mining.
However, as-prepared graphene easily agglomerate
irreversibly due to the large surface area and surface energy, which makes it difficult to disperse in
most of solvents [3,10] and increases the difficulty
in application. To this end, a number of research
groups [15-21] have produced the well-dispersed
graphene sheets in solvents with decorating surfactants or stabilizers through physical and chemical
methods. Although functionalization of graphene
enables us to obtain isolated graphene with good
dispersibility, this processing may destroy the
unique properties of graphene.
Actually, graphene composites, especially for
polymer matrix composites, are regarded as one of
the most promising industrial products in many ap-
Graphene, a nanometer-thick two-dimensional analog of fullerenes and carbon nanotubes [1], has recently sparked great excitement in the scientific
community given its excellent mechanical, thermal
and electronic properties [2]. In addition, as a flexible material with large specific surface area,
graphene has shown to be an outstanding buildingblock [3,4]. Despite its short history, graphene has
revealed various potential applications [5-9] in the
construction of devices, sensors, transparent conductive films, and composites. However, practical
application of graphene requires its large scale production primarily [3,10].
Up until now, versatile methods have been developed for preparation of graphene and its derivatives, such as mechanical exfoliation [1], epitaxial
growth [11], chemical reduction [3], liquid phase
exfoliation [12], chemical vapor deposition (CVD)
Corresponding author: Guo-Jjian Wang, e-mail: [email protected]
s(& 5Tf
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Surface properties of graphene: relationship to graphene-polymer composites
plications [22]. For graphene-polymer composites,
the property of composites is determined mainly by
the synergistic combination of high specific surface
area of graphene, strong filler-matrix interfacial adhesion as well as the exceptional properties of
graphene, and also by the essential properties of
the matrix. Importantly, the performance of composites can be maximized if an effective load transfer
from the matrix to the graphene is guaranteed, because graphene share major portion of the load to
which the composites structure is subjected. This
is made possible by ensuring appropriate interfacial adhesion or compatibility between the matrix
and the graphene. The interfacial adhesion is determined by matrix properties and surface properties
of graphene [23], such as the total surface area of
graphene available for contact with matrix molecules;
surface roughness of graphene, which may allow
for mechanical interlocking; the chemistry structure
and surface energy of graphene, which determine
whether the graphene will be wetted by the matrix,
as well as by the surface functional groups for forming attractive interactions, in particular, chemical
bonds with matrices or polar interactions (such as
Lewis acid-base interactions and hydrogen bonds)
with matrices [24]. Therefore, the surface properties of graphene and surface/ interfacial interaction
between graphene and matrix play crucial roles in
control of the properties of composites. Furthermore,
surface properties are especially important for hybrid materials and coatings which are used in biomedical, electronic and energy applications [25,26].
To best of our knowledge, surface properties and
interface energies are the most important physical
attributes of nanostructures [27,28] which are considered as main factor affecting interfacial adhesion
and surface processing of composites essentially
[29,30]. Importantly, it has been realized that the
anomalous surface energy of nanostructures always
induces many novel phenomena which will require
supporting of new technology and theory. Thus,
considerable researches have been carried out on
the surface characterization and surface modifications of graphene, which have been reviewed in more
detail in many literatures [31-33]. However, surface
properties of graphene as the most fundamental issue still has not been understood clearly. Therefore, it is necessary to realize and determine surface properties of graphene. In this review, we focus
on surface properties of graphene which prepared
from graphite oxide. Several recent reviews have
already addressed the synthesis, composites and
functionalization of graphene. Hence, these will not
be discussed in detail here. We will survey for the
61
Fig. 1. (a) Schematic diagram of typical configuration of graphene; (b) TEM atomic resolution image
of graphene; (c) STM topographic image from a
single layer of graphene (adapted from ref. [34-36]).
status and progress of research of surface properties of graphene, and aim to provide an overview of
the different surface properties of graphene, for example, microstructure, surface area, surface chemical composition, as well as surface energy, and the
determination techniques of the surface properties
of graphene. Moreover, tailoring of these surface
properties via surface treatments and the effects on
the graphene-polymer matrix interface are briefly
discussed.
2. SURFACE STRUCTURE AND
MORPHOLOGY OF GRAPHENE
Surface properties of graphene are intimately related
to the graphitic basal plane character of the graphite and can be illustrated in terms of the graphite
structure. Theoretically, the graphene honeycomb
lattice is composed of sp2 hybridization carbon atoms bonded together with bonds. The remaining
n b
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three neighboring carbon atoms to form a orbital
that contributes to a delocalized network of electrons. Based on microstructure analysis, the typical configuration of single-layer graphene is not complete flat layer, but there are many initiative wrinkles
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face, which has been demonstrated by Monte Carlo
simulation [34], transmission electron microscopy
(TEM) [35] and scanning tunneling microscopy
(STM) [36], as shown in Fig. 1. Further, the correlation between fluctuations and electrical properties
of graphene was studied exclusively by using STM
technique [37,38]. Studies indicated that the change
62
J.-F. Dai, G.-J. Wang, L. Ma and Ch.-K. Wu
Table 1. Specific surface area (BET) of different graphene samples determined using N2 adsorption.
Samples
Preparation methods
SBET (m2y
W-1)
Ref.
RGO
RGO
Al-GN
MEGN
CMG
TEGN
TEGN
TEGN
TEGN
FGN
Reduced by hydrazine
Reduced by hydrazine hydrate
Reduced by aluminum power
Microwave assisted exfoliation
Chemically modified and reduced graphene
Low-temperature exfoliation under vaccum
Thermal exfoliation of GO at 1050 r
C under Ar
Thermal exfoliation of GO at 1050 r
C under Ar
Thermal exfoliation of GO at 800 r
C in H2 stream
Based on Ref. [56], with activation of KOH,
thermal exfoliation at 800 r
7e TUb
5b
320
466
365
463
705
~400
650
600~700
940
3100
[53]
[54]
[55]
[56]
[57]
[58]
[59]
[48,60]
[61]
[62]
of local electrical properties is negligible or limited
when corrugations are under 0.5 nm in height,
whereas strained graphene for bigger ripples (2~3
nm in height) exhibit tunneling conductance [39,40].
The altered electrical property of graphene with structural adjustment is likely important for possible application in graphene devices [41].
Huge specific surface area is an important feature of graphene that determines the interface interaction between graphene and matrix in composites.
N2 adsorption is a commonly used analytical technique for the determination of the specific surface
area of solid materials, and the data are usually
analyzed using the Brunauer-Emmett-Teller (BET)
theory [42]. Until now, there have been several reports on specific surface area of graphene, a few
examples were given in Table 1. Although the theoretical specific surface area of graphene is 2630
m 2y
W-1 [3], the as-prepared graphene samples (as
mentioned in Table 1) have typical experimental values of the specific surface area ranging from ~100
to ~1000 m2y
W-1, which is due to surface area of
graphene depend strongly on their layers and structure. The results further show that graphene manufactured by thermal exfoliation at high temperature
has more single-, few-layer structure, hence has
specific higher surface area. Besides, graphene
treated via chemical modification also can modulate the surface area of graphene significantly to
some extent [43]. Improvement in the interfacial interaction or practical adhesion between the
graphene and polymer matrices/metal oxides has
been demonstrated by increasing the graphene surface area and surface roughness [3,44-47], which
could be mainly attributed to mechanical interlocking and physical adsorption. For instance, PMMAbased nanocomposites filled with thermal exfoliated
graphene sheets (TEGN) showed more superb thermal, mechanical, and rheological property than composites reinforced with expandable graphite (EG) at
equivalent loading [48], and the images of electron
microscope (as seen in Fig. 2) and experimental
data suggested significant reinforcement from TEGN
is attributed to strong interfacial interaction augmented by mechanical interlocking with the host
polymer due to large surface area and wrinkled
morphology of the TEGN [48-50]. Aside from the
effect of roughness of graphene, Bruneton et al.
[51,52] proposed that a strong adhesion required
carbon materials uniform occurrence of accessible
edges (which can be created by chemical surface
treatments). Chemical surface treatments of
Fig. 2. SEM images of graphene composite: (a) EG-PMMA; (b) TEGN-PMMA (adapted from ref. [48]).
Surface properties of graphene: relationship to graphene-polymer composites
63
Table 2. Surface composition and C1s peaks of different graphene samples determined using XPS.
Samples
Treatment
C:O ratio
N(%)
sp3 hybridization
component (%)
Ref.
GO
Chemical Oxidation
of graphite
Reduced via
chemical methods
Thermal exfoliation of GO
1. Treated via
chemical methods;
2. Thermal exfoliation
1.9~2.8
0
~70
[4,65,66]
4~10.3
<3
~27~13.5
[66-68]
5.6~10.0
>246
0
<0.5
~18~14.7
~2
[48,59,69]
[62,70]
RGN
TEGN
FGN
graphene do contribute to the performance of composites significantly. However, the surface functional
groups introduced during the chemical surface treatments would change the surface chemical composition of graphene, which will be discussed in the
following section.
3. SURFACE COMPOSITION AND
CHEMISTRY OF GRAPHENE
Pristine, ideal graphene is only a single layer of
carbon atom with simplex sp2 hybridization. However, reduced graphene obtained from the reduction
of graphene oxide still has tiny oxygen-containing
groups on its surface. The presence of these functional groups changes graphene structure, thus influences the properties of graphene. Consequently,
study of the composition of graphene is a priority
during any application fields. X-ray photoelectron
spectroscopy (XPS) is a technique that allows the
composition of the outermost few atomic layers of
solid surface to be analyzed. It is commonly used
to characterize the surface composition of graphene
as well as the oxidation state of elements present
in the graphene surface by analyzing the chemical
shift of the atomic core level binding energies
[32,63,64]. In Table 2, the surface composition of
typical graphene oxide (GO), chemical reduced
graphene (RGN), thermal exfoliation graphene
(TEGN) and functionalized graphene (FGN) determined by XPS is summarized. It is found that the
main differences between the various graphene
samples are their carbon/oxygen ratios (C:O) and
degree of sp3 hybridization, which are related to the
preparation process and the surface treatment of
graphene.
Although the pristine graphene has the highest
theoretical strength, its perfect honeycomb lattice
makes graphene chemical inertness. As we known,
the presence of functional groups on graphene sur-
face can modifies its surface chemistry, even can
benefits dispersibility in some solvents and matrixes
[71]. Bao et al. [66], Liang et al. [72], and Wang et
al. [73] prepared GO/PVA composites by solution
processing method. The result shows that tensile
strength of the composites increases with the enhancement of oxygen content of GO. The authors
ascribed the result to two possible mechanisms.
First, interfacial interactions between GO and PVA
matrix is thought to be controlled by chemical bonding between suitable functional groups presented
on graphene surfaces; and second, mechanical interlocking due to the enhanced nanoscale surface
roughness that have been elaborated in this review
previously. Whereas, the situation with RGO and
TEGN is much different, the surface defects in carbon lattice due to the severe oxidation process and
poor dispersion in polymer matrix due to the functional groups removal process have reverse effects
on the performance of composites [72,74,75]. Even
if the mechanical property of RGO and TEGN is
much higher than GO, the improvement of performance of composites is still relative small [66].
The interaction of graphene and polymer matrix
at the interface has significant implications for the
final composites properties. The tailoring of interfacial interaction and dispersion by functionalization
and modification between graphene and polymer
matrix has been focused. The methods of
functionalization and modification of graphene have
already reported elsewhere. Hence, we will not repeat again. A recent in-situ polymerization strategy
has been shown to provide strong interfacial interaction and good dispersion between graphene and
polymer matrix directly [76]. The comparative studies of both GO and modified graphene oxide (MGO)
based polyimide (PI) nanocomposites were carried
out by Wang et al. [77] and Liao et al. [78]. Their
results all reveal that MGO/PI composites exhibit
greater mechanical properties than that of GO/PI
64
J.-F. Dai, G.-J. Wang, L. Ma and Ch.-K. Wu
Fig. 3. SEM images of fractured surface of GO/PI (a, b) and MGO/PI (c, d) composites; model of the
interphase structure of GO/PI (e) and MGO/PI (f) composites (adapted from ref. [77]).
composites. The enhancement to some extent of
the mechanical properties of the composites was
ascribed to better homogeneous dispersion of MGO
in the matrix than that of GO/PI composites, as
well as strong interfacial interactions between both
components (as shown in Figs. 3a-3d). In order to
explain this phenomenon accurately, the authors
simulated the process (as depicted in Figs. 3e-3f),
suggesting that graphene surface modified by polymer vary the surface composition and surface properties of graphene, thus form a flexible interphase
between polymer and graphene to provide an effective path for load transfer.
4. WETTABILITY OF GRAPHENE
The interaction between a liquid and graphene surface is manifested in the wettability of graphene,
which has attracted more and more interests in the
field of surface chemistry, physics, and materials
science because it may have lots of practical application [26,79]. However, quantitative knowledge of
wetting properties of graphene is still lacking. Experimentally, the wettability of graphene is commonly quantified by measuring contact angles (CA,
). When a liquid drop is placed on a flat solid substrate, it either spreads into a thin continuous film
or beads up. The is defined as the angle at which
a liquid-vapor interface meets the solid surface. Even
if graphene has already been recognized as a hydrophobic material [80], extensive works are still
ongoing for better understanding the wetting properties of graphene.
Recently, Wang et al. [81] reported that the water contact angle of graphene films produced by
chemical exfoliation (127.0r
) is much higher than
that of graphite (98.3r
). While Shin et al. [82] prepared single-, bi-, and multi-layer graphene by epitaxial method which have similar water contact angle
to graphite (~92r
). Interestingly, these two contradictory results are supported by consistent evidence
from water contact angle measurements. It can be
ascribed to different roughness of the tested
samples. Obviously, the irregularly stacked graphene
films comprised microstructure and nanostructure
(as shown in Fig. 4), which enhanced the CA and
hydrophobicity of graphene [83]. Although both
graphene film and graphene layer are the same kind
of material, their wettability is changed with their
different surface morphology. As a result, the
wettability of both graphene film and graphene sheet
should be further discussed respectively.
: bd
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gested that there is no thickness dependence of
the CA of water from measurements on single-, biand multi-layer graphene coated on SiC. However,
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on different layers of graphene sheets depending
on the type of substrate [86]. In their experiment, a
series of different layers of graphene sheet was prepared on Cu substrate using CVD method, and then
was transferred onto Si, Au, and glass substrates,
respectively. As shown in Fig. 5, the measurement
results of CA showed that graphene is wetting transparent for Cu substrate but not for glass, when the
layer of graphene is less than 4. Beyond four
graphene layers there is a relatively sharp increase
in the CA value. Finally, with increase of layers of
graphene, especially when it is more than 6, the CA
Surface properties of graphene: relationship to graphene-polymer composites
65
Fig. 4. SEM images of graphene layers (a, b) and graphene films (c, d). (adapted from ref.[84,85]).
Fig. 5. Water contact angle measurements on Cu and glass with different layers of graphene (adapted from
ref. [86]).
value of graphene tends to be stable and achieve
the CA value of the graphite. Subsequently, the same
results of wetting experiments were also obtained
by performing on Si and Au substrates. Molecular
dynamics simulations and theoretical predictions
further confirm that wettability of graphene layer is
related to thickness of graphene and nature of substrates. Because the CA on hydrophilic substrate
(such as glass) is dominated by short-range chemical
forces, the presence of graphene between hydrophilic substrate and water will significantly disrupt
the chemical bonding at their interface. However,
the CA on the hydrophobic surface (such as Cu, Si,
and Au) is dominated by the relatively long-range
van der Waals interactions, and is maintained for
less than four graphene layers. This conclusion was
further reported by Shin et al. [87] thoroughly. They
pointed out that a single layer graphene becomes
more transparent for wetting on hydrophilic substrates and more opaque for wetting on hydropho-
bic substrates. The finding also implies that
graphene layer can be used as an ideal material for
protecting reactive substrate surfaces without changing wetting properties of substrate materials [8890].
In addition, the wetting behavior of graphene
sheet not only depends on the layer numbers of
graphene and the substrates for preparation of
graphene, but also on the surface chemical composition of graphene. Shin et al. [82] studied the wetting behavior of various modified graphene and found
that their wettability is related to the oxygen-containing groups and even can be modulated by optimized chemical surface treatments technology (CA
in water, as shown in Table 3). Furthermore, chemical surface treatments of graphene show much more
intense influences on wettability of graphene than
variation layer of graphene at the same substrate.
In the present study, for the graphene film, it always shows highly hydrophobic behavior due to
66
J.-F. Dai, G.-J. Wang, L. Ma and Ch.-K. Wu
Table 3. The contact angle ( ) of sample to water.
Sample
/r
Singlegraphene
Bigraphene
Multigraphene
O2 Plasma
treated
One day after
plasma treated
Annealed
92.5
91.9
92.7
55.1
72.4
87.3
The data were adapted from ref. [82]
microstructure and nanostructure surface roughness
[82,91]. Zhang et al. [91] performed the experiments
on the correlation of the CA with the centrifugal
speeds (as shown in Fig. 6a). It was found that the
hydrophobicity of the graphene film is governed and
modulated by the morphology of film, especially by
microstructure of film, and is hardly influenced by
layer numbers of graphene and the substrates for
preparation of graphene. Consequently, there is
many potential controllable manipulation of the wetting action of the graphene film. As mentioned above,
chemical surface treatment of graphene has significantly influence on wettability of graphene. It means
that this method also has similar effects on
wettability of graphene film, because of the graphene
films always comprising the graphene layer. Based
on the experiment of relationship between the morphology and the hydrophobicity of graphene film,
Zhang et al. [91] further reported the tunable
wettability of graphene film by interaction with ethanol, showing that the wettability of graphene film
can be reversibly modified through exposure in air
and UV irradiation (from hydrophilic to
superhydrophobic, again to hydrophilic, as seen in
Figs. 6b and 6c). The authors ascribed the results
to the adsorption and desorption of water and oxygen molecules on the graphene surface. Obviously,
the adsorption and desorption process significantly
affect the surface components and surface energies of graphene film. Therefore, the wetting behav-
Fig. 6. (a) CA of graphene films by different centrifugal speeds, inset: SEM images of the corresponding
films by different centrifugal speeds; (b) The relationship between the CA of the graphene film and its
exposure time in air; (c) The reversible wettability transition of graphene film by exposure in UV irradiation
and in air (adapted from ref. [91]).
Surface properties of graphene: relationship to graphene-polymer composites
ior of graphene film also varies with the conversion
of the adsorption and desorption process. Rafiee et
al. [92] reported functional graphene film that the
wetting behavior of film can be tailored over a wide
range (from superhydrophobic to superhydrophilic)
by controlling relative proportion of acetone and water
in preparation process. These results demonstrate
that the surface chemistry of graphene is very important to alter the wettability of graphene essentially. Very recently, our group [93] also studied the
relationship between proportion of solvent and surface composition of graphene oxide film. It was found
that the solvent with carbonyl group can adsorb on
the surface of the graphene oxide film. Therefore,
the roughness and surface chemistry of graphene
are changed obviously which lead to the variation of
wetting behavior.
With all of the above results, we suggest that
the role of chemical heterogeneities on the graphene
surface has very important influence for the wetting
properties of graphene.
5. SURFACE ENERGY OF GRAPHENE
The investigation of the surface energy of graphene
is of great importance, because it strongly influences
the wettability of graphene and the formation of the
graphene-based composites interface. The surface
energy of graphene can be determined from the
measurement of contact angles of suitable test liquids on graphene surface using different surface
energy models following essentially two approaches:
1) the equation of state approach and 2) the surface
energy component approach [94,95]. While the
equation of state approach only provides the solid
surface energy, the various surface energy component approaches can provide further information,
such as dispersive and non-dispersive component
of graphene, including polar or acid-base components. Further details of these models can be found
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Wang et al. [81] employed contact angle method to
obtained surface free energy of RGO, GO, and graphite, and found that the surface free energy of them
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]-2 ,( ]>y
]-2, Q T .]>y
]-2, respectively. This study indicates that oxidative surface modification considerably increased the surface energy. On the other hand, reducing material
dimension from 3D to 2D may reduce the wettability
and decrease the interfacial adhesion with liquids.
However, Shin et al.[87] calculated the surface energy of monolayer, bi-layer, and tri-layer graphene
by assuming a continuous distribution of carbon
atoms and using a Lennard-Jones carbon-carbon
67
potential, and found that it is much higher than that
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b
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sults of surface energy obtained from CA may be
severely flawed for the graphene surface character.
Moreover, Raj et al. [79] further pointed out that static
contact angle measurements for wettability and
surface energy of graphene cannot solely be used
on such rough, defective and chemical heterogeneous surface. The presence of chemical inhomogeneity and the surface roughness of graphene make
the contact angle measurements less appropriate
for evaluation of surface energies [99]. In fact, it has
been reported that methods based on contact angle
measurements can influenced the facticity of the
test results, particularly those concerning acid-base
characteristic of the surface of the materials [100].
Inverse gas chromatography (IGC) is also used
to investigate the surface energies of carbon materials [101-105], such as carbon nanotubes, carbon
fibers, and carbon black. In the IGC experiment,
carbon materials are used as the stationary phase,
and a mobile gas or vapor phase with well-known
properties is injected as a probe into the column
filled with carbon material at a fixed carrier gas flow
rate. It is noted that this efficient and sensitive technique requires only a small amount of sample for
determination of surface energy. Moreover, several
thermodynamic quantities (i.e. free energy of adsorption and enthalpy of adsorption), the polar components of surface energy and acid-base properties
of the materials can also be ascertained easily using IGC technique [106]. Recently, Shaffer et al.
[107] achieved the surface properties of as-received
and modified carbon nanotubes (CNTs) using IGC,
and obtained a series of thermodynamic surface
parameters (such as dispersive surface energies,
specific surface energies, electron acceptor (KA) and
donor (KD) numbers, and adsorption capacities). In
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eb
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deconvolution of contributions of structural and
chemical surface energies of CNTs by IGC with
branched probes, and given out that the specific
surface energies is depended on the modification
treatment markedly. Inspired by these works, IGC
is also adopted to determine the thermodynamic
surface properties of graphene. In a more recent
study by Otyepka et al. [108] the adsorption enthalpies of organic molecules on graphene were
TUd
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b] /[SQy
mol-1 VbTY
S
X b]Ud
XQ Ud ) [S
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the interaction energy and specific surface energy
VWb
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b] Cd
i
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cg b
[ eb
68
J.-F. Dai, G.-J. Wang, L. Ma and Ch.-K. Wu
Table 4. Thermodynamic surface properties of graphite, GO, RGO, EG-RGO, and COOH-GO at 40 r
7
Samples
GO
COOH-GO
EG-RGO
RGO
Graphite
d
s
]>
y
]-2)
-./v)
.))v (
/(.v
&,.v )
( ,v).
p
s
]>
y
]-2)
- v))
. (v)
)-)v)
.& v
)/,v &
- GDCM [>
y
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sp
5.13
5.84
3.89
1.66
0.75
-1
)
- GEtAc [>y
]
sp
12.1
15.2
10.4
5.29
5.78
-1
)
KA
KD
0.35
0.52
0.30
0.29
0.28
0.66
0.95
0.49
0.35
0.18
The data adapted from ref. [109,110]
group [109,110] further studied the thermodynamic
surface properties of graphite, graphene oxide (GO),
reduced graphene oxide (RGO), ethylene glycoltreated graphene oxide (EG-RGO), and carboxylated graphene oxide (COOH-GO) using IGC. The
data of thermodynamic surface parameters were
summarized in Table 4. The results showed that
the decrease of oxygen-containing groups of materials reduce the polar component while increase the
dispersive surface energies, which may be attributed to the change of polar functional groups and
local defects. In Table 4, the acid-base characteristic of the as-prepared materials was also listed. It
was found that KD is bigger than KA indicative of a
Lewis-base surface for GO. As the same, the surface character of the other as-prepared materials
was also characterized: COOH-GO exhibits Lewisbase character, EG-RGO, and RGO both show
amphoteric but more Lewis-base character, while
graphite reveals Lewis-acid character. Consequently,
it can be concluded that the type and amount of
defects and functional groups on the surface of
graphene would alter the surface properties of
graphene as well as Lewis acid-base surface character of graphene. Combined with the results of
enhanced mechanical properties of graphene-based
nanocomposites [66,73,77,78] as mentioned in section two, it reveals that any surface treatments to
modify surface chemistry of graphene could lead to
the decrease of dispersive surface energy whilst
change of surface character of Lewis acid-base,
which will make better interfacial interaction and
dispersion between graphene and different polymers.
Therefore, both surface energy and surface character of Lewis acid-base could be fast and useful measurement parameters for analyzing surface treatment. Moreover, determination of surface energies
of graphene can also help to establish Hansen-like
solubility parameters of graphene [110-112], for
choosing suitable solvents to improve dispersion of
graphene theoretically. As a result, evaluation of
surface energies and surface character of Lewis acid-
base of graphene would facilitate preparation of
graphene-polymer composites and development of
graphene-based materials.
6. CONCLUSION
Graphene is considered as one of the best reinforcements for composite materials. Currently, the
development of graphene-based nanocomposites
with enhanced mechanical properties and additional
functionality (thermal, electrical, and optical properties, etc.) is ongoing. In order to fully utilize the
advantages of graphene, a comprehensive understanding of graphene surface properties is crucial,
as they determine the interfacial adhesion and compatibility at graphene-matrix interface and the overall composite performance. This review endeavors
to sum up the current research status on surface
properties of graphene that have predominated in
the application field of graphene-based composites.
The influence factors of surface properties of
graphene, such like microstructure, surface area,
surface chemistry and composition, as well as surface energy, and the techniques that can be used
to determine the surface properties of graphene were
discussed. The conclusion indicated that to tailor
the surface properties of graphene by modification
of graphene surface chemistry is essential to receive a better compatible composite which can improves the interfacial interaction via 1) mechanical
interlocking by increasing surface area and wrinkle,
2) chemical bonding by functional groups on
graphene surface, such as van der Waals and hydrogen bonding, which also leads to the decrease
of the dispersive surface energy of graphene whilst
the improvement of wettability of the graphene for
the matrix. With no doubt, further developments in
surface characterization techniques and graphene
surface treatments will lead to improved understanding of the surface properties of graphene and better
control of interfacial properties in composites. In this
way, evaluation of surface properties of graphene is
Surface properties of graphene: relationship to graphene-polymer composites
desirable, which would be used to guide the processing and application in graphene-based
nanocomposites in the future.
REFERENCES
[1] K.S. Novoselov, A.K. Geim, S.V. Morozov,
D. Jiang, Y. Zhang, S.V. Dubonos, I.V.
Grigorieva and A.A. Firsov // Science 306
(2004) 666.
[2] A.K. Geim // Science 324 (2009) 1530.
[3] S. Stankovich, D.A. Dikin, G.H.B. Dommett,
K.M. Kohlhaas, E.J. Zimney, E.A. Stach, R.D.
Piner, S.T. Nguyen and R.S. Ruoff // Nature
442 (2006) 282.
[4] O.C. Compton and S.T. Nguyen // Small
6 (2010) 711-723.
[5] Y. Sui and J. Appenzeller // Nano Lett.
9 (2009) 2973..
[6] C. Shan, H. Yang, J. Song, D. Han, A. Ivaska
and L. Niu // Anal. Chem. 81 (2009) 2378.
[7] M. Zhou, Y. Zhai and S. Dong // Anal. Chem.
81 (2009) 5603.
[8] S. Guo, S. Dong and E. Wang // ACS Nano
4 (2009) 547.
[9] A. Cao, Z. Liu, S. Chu, M. Wu, Z. Ye, Z. Cai,
Y. Chang, S. Wang, Q. Gong and Y. Liu // Adv.
Mater. (Weinheim, Ger.) 22 (2010) 103.
[10] C.J. Shih, S.C. Lin, M.S. Strano and
D. Blankschtein // J. Am. Chem. Soc. 132
(2010) 14638.
[11] C. Berger, Z. Song, T. Li, X. Li, A.Y.
Ogbazghi, R. Feng, Z. Dai, A.N. Marchenkov,
E.H. Conrad, P.N. First and W.A. de Heer //
J. Phys. Chem. B 108 (2004) 19912.
[12] V.C. Tung, M.J. Allen, Y. Yang and R.B.
Kaner // Nat. Nanotechnol. 4 (2009) 25.
[13] C.-a. Di, D. Wei, G. Yu, Y. Liu, Y. Guo and
D. Zhu // Adv. Mater. 20 (2008) 3289.
O P> Ke K DY
ceQQ T AqU %
%Chem.
Rev. 107 (2007) 718.
[15] S. Stankovich, R.D. Piner, X. Chen, N. Wu,
S.T. Nguyen and R.S. Ruoff // J. Mater.
Chem. 16 (2006) 155.
[16] R. Muszynski, B. Seger and P.V. Kamat //
J. Phys. Chem. C 112 (2008) 526.
[17] G. Williams, B. Seger and P.V. Kamat //
ACS Nano 2 (2008) 1487.
[18] Y. Xu, H. Bai, G. Lu, C. Li and G. Shi // J.
Am. Chem. Soc. 130 (2008) 5856.
[19] X. Li, X. Wang, L. Zhang, S. Lee and H. Dai //
Science 319 (2008) 1229.
[20] X. Li, G. Zhang, X. Bai, X. Sun, X. Wang,
E. Wang and H. Dai // Nat. Nanotechnol.
3 (2008) 538.
69
[21] Y. Hernandez, V. Nicolosi, M. Lotya, F.M.
Blighe, Z. Sun, S. De, I.T. McGovern,
6 < Q T A 6i
bU M ;e x >>
Boland, P. Niraj, G. Duesberg,
S. Krishnamurthy, R. Goodhue, J. Hutchison,
V. Scardaci, A.C. Ferrari and J.N. Coleman //
Nat. Nanotechnol. 3 (2008) 563.
[22] J. Longun, G. Walker and J.O. Iroh // Carbon
63 (2013) 9.
[23] J. Du and H.-M. Cheng // Macromolecular
Chemistry and Physics 213 (2012) 1060.
[24] M. Peressi, Surface Functionalization of
Graphene. In: Graphene Chemistry, (John
Wiley & Sons, Ltd, 2013) p. 233.
O
( P< 7XU A 6 AqUb > ;Y
] b
U ;;
Wallace and D. Li // Adv. Mater. 20 (2008)
3557.
[26] Y.-L. Zhang, H. Xia, E. Kim and H.-B. Sun //
Soft Matter 8 (2012) 11217.
[27] G. Ouyang, C.X. Wang and G.W. Yang //
Chem. Rev. 109 (2009) 4221.
[28] Y.X. Zhuang and O. Hansen // Langmuir 25
(2009) 5437.
[29] C.H. Sun and J.C. Berg // J. Colloid Interface
Sci. 260 (2003) 443.
[30] P. Kowalczyk, K. Kaneko, A.P. Terzyk,
H. Tanaka, H. Kanoh and P.A. Gauden //
J. Colloid Interface Sci. 291 (2005) 334.
[31] M.J. Allen, V.C. Tung and R.B. Kaner //
Chemical Reviews 110 (2010) 132.
[32] D. Chen, H. Feng and J. Li // Chemical
Reviews 112 (2012) 6027.
[33] V. Georgakilas, M. Otyepka, A.B. Bourlinos,
V. Chandra, N. Kim, K.C. Kemp, P. Hobza,
R. Zboril and K.S. Kim // Chemical Reviews
112 (2012) 6156.
[34] A. Fasolino, J.H. Los and M.I. Katsnelson //
Nat. Mater. 6 (2007) 858.
[35] J.C. Meyer, A.K. Geim, M.I. Katsnelson, K.S.
Novoselov, T.J. Booth and S. Roth // Nature
446 (2007) 60.
[36] E. Stolyarova, K.T. Rim, S. Ryu,
J. Maultzsch, P. Kim, L.E. Bru, T.F. Heinz,
M.S. Hybertsen and G.W. Flynn // Proc.
Natl. Acad. Sci. U. S. A. 104 (2007) 9209.
[37] A. Deshpande, W. Bao, F. Miao, C.N. Lau
and B.J. LeRoy // Phys. Rev. B 79 (2009)
205411.
[38] Y. Zhang, V.W. Brar, C. Girit, A. Zettl and
M.F. Crommie // Nat. Phys. 5 (2009) 722.
[39] M.L. Teague, A.P. Lai, J. Velasco, C.R.
Hughes, A.D. Beyer, M.W. Bockrath, C.N.
Lau and N.C. Yeh // Nano Lett. 9 (2009)
2542.
70
[40] K. Xu, P. Cao and J.R. Heath // Nano Lett.
9 (2009) 4446.
[41] W. Bao, F. Miao, Z. Chen, H. Zhang,
W. Jang, C. Dames and C.N. Lau // Nat
Nano 4 (2009) 56.
O(PA HX ]]Uc F pX Q TA :b
pRQ%
%
J. Phys. Chem. B 104 (2000) 7932.
[43] Q. Tang, Z. Zhou and Z. Chen // Nanoscale
5 (2013) 4541.
[44] B. Chieng, N. Ibrahim and W.W. Yunus //
Polym.-Plast. Technol. Eng. 51 (2012) 791.
[45] Q. Liu, X. Zhou, X. Fan, C. Zhu, X. Yao and
Z. Liu // Polym.-Plast. Technol. Eng. 51
(2012) 251.
[46] C.N.R. Rao, A.K. Sood, K.S. Subrahmanyam
and A. Govindaraj // Angew. Chem. Int. Ed.
48 (2009) 7752.
[47] S. Chen, J. Zhu, X. Wu, Q. Han and X. Wang
// ACS Nano 4 (2010) 2822.
[48] T. Ramanathan, A.A. Abdala, S. Stankovich,
D.A. Dikin, H.A. M., R.D. Piner, D.H.
Adamson, H.C. Schniepp, Chen X, R.S.
Ruoff, S.T. Nguyen, I.A. Aksay, R.K.
Db
eTx
< ]]UQ T@7 6b
Yc %
%Nat.
Nanotechnol. 3 (2008) 327.
[49] X. Huang, X. Qi, F. Boey and H. Zhang //
Chemical Society Reviews 41 (2012) 666.
[50] A. Dasari, Z.-Z. Yu and Y.-W. Mai // Polymer
50 (2009) 4112.
[51] E. Bruneton, B. Narcy and A. Oberlin //
Carbon 35 (1997) 1593.
[52] E. Bruneton, B. Narcy and A. Oberlin //
Carbon 35 (1997) 1599.
[53] Y. Wang, Z. Shi, Y. Huang, Y. Ma, C. Wang,
M. Chen and Y. Chen // J. Phys. Chem. C
113 (2009) 13103.
[54] S. Stankovich, D.A. Dikin, R.D. Piner, K.A.
Kohlhaas, A. Kleinhammes, Y. Jia, Y. Wu,
S.T. Nguyen and R.S. Ruoff // Carbon 45
(2007) 1558.
[55] Z. Fan, K. Wang, T. Wei, J. Yan, L. Song and
B. Shao // Carbon 48 (2010) 1686.
[56] Y. Zhu, S. Murali, M.D. Stoller, A.
Velamakanni, R.D. Piner and R.S. Ruoff //
Carbon 48 (2010) 2118.
[57] M.D. Stoller, S. Park, Y. Zhu, J. An and R.S.
Ruoff // Nano Lett. 8 (2008) 3498.
[58] W. Lv, D.-M. Tang, Y.-B. He, C.-H. You, Z.-Q.
Shi, X.-C. Chen, C.-M. Chen, P.-X. Hou,
C. Liu and Q.-H. Yang // ACS Nano 3 (2009)
3730.
[59] H.C. Schniepp, J.-L. Li, M.J. McAllister,
H. Sai, M. Herrera-Alonso, D.H. Adamson,
F Db
eTx
X ]]U F 7Qb85 GQf
YUQ T
J.-F. Dai, G.-J. Wang, L. Ma and Ch.-K. Wu
I.A. Aksay // J. Phys. Chem. B 110 (2006)
8535.
[60] M.J. McAllister, J.-L. Li, D.H. Adamson, H.C.
Schniepp, A.A. Abdala, J. Liu, M. HerreraAlonso, D.L. Milius, R. Car, R.K.
Db
eTx
X ]]UQ T 5 5[cQi%
%Chem. Mater.
19 (2007) 4396.
[61] K. Evanoff, A. Magasinski, J. Yang and
G. Yushin // Advanced Energy Materials
1 (2011) 495.
[62] Y. Zhu, S. Murali, M.D. Stoller, K.J. Ganesh,
W. Cai, P.J. Ferreira, A. Pirkle, R.M.
Wallace, K.A. Cychosz, M. Thommes,
D. Su, E.A. Stach and R.S. Ruoff // Science
332 (2011) 1537.
[63] S. Pei and H.-M. Cheng // Carbon 50 (2011)
3210.
[64] D.R. Dreyer, S. Park, C.W. Bielawski and
R.S. Ruoff // Chemical Society Reviews 39
(2010) 228.
[65] A. Ganguly, S. Sharma, P. Papakonstantinou
and J. Hamilton // J. Phys. Chem. C 115
(2011) 17009.
[66] C. Bao, Y. Guo, L. Song and Y. Hu //
J. Mater. Chem. 21 (2011) 13942.
[67] J. Paredes, S. Villar-Rodil, P. SolisFernandez, A. Martinez-Alonso and
J. Tascon // Langmuir 25 (2009) 5957.
[68] H. Shin, K.K. Kim, A. Benayad, S. Yoon,
H.K. Park, I. Jung, M.H. Jin, H. Jeong, J.M.
Kim and J. Choi // Adv. Funct. Mater. 19
(2009) 1987.
[69] Z.-S. Wu, W. Ren, L. Gao, B. Liu, C. Jiang
and H.-M. Cheng // Carbon 47 (2009) 49.
[70] W. Gao, L.B. Alemany, L. Ci and P.M. Ajayan
// Nature Chem. 1 (2009) 403.
[71] J.I. Paredes, S. Villar-Rodil, A. MartnezAlonso and J.M.D. Tascn // Langmuir 24
(2008) 10560.
[72] J. Liang, Y. Huang, L. Zhang, Y. Wang,
Y. Ma, T. Guo and Y. Chen // Adv. Funct.
Mater. 19 (2009) 2297.
[73] J. Wang, X. Wang, C. Xu, M. Zhang and
X. Shang // Polym. Int. 60 (2011) 816.
[74] H. Kim and C.W. Macosko //
Macromolecules 41 (2008) 3317.
O
-P
7 ; ]UjBQf
Qb
b >7 AUi
UbFG
Sundaram, A. Chuvilin, S. Kurasch,
M. Burghard, K. Kern and U. Kaiser // Nano
Lett. 10 (2010) 1144.
[76] V. Singh, D. Joung, L. Zhai, S. Das, S.I.
Khondaker and S. Seal // Progress in
materials science 56 (2011) 1178.
Surface properties of graphene: relationship to graphene-polymer composites
[77] J.-Y. Wang, S.-Y. Yang, Y.-L. Huang, H.-W.
Tien, W.-K. Chin and C.-C.M. Ma // J. Mater.
Chem. 21 (2011) 13569.
[78] W.-H. Liao, S.-Y. Yang, J.-Y. Wang, H.-W.
Tien, S.-T. Hsiao, Y.-S. Wang, S.-M. Li,
C.-C.M. Ma and Y.-F. Wu // ACS Appl.
Mater. Interfaces 5 (2013) 869.
[79] R. Raj, S.C. Maroo and E.N. Wang // Nano
Lett. 13 (2013) 1509.
[80] O. Leenaerts, B. Partoens and F.M. Peeters
// Phys. Rev. B 79 (2009) 235440.
[81] S.R. Wang, Y. Zhang, N. Abidi and
L. Cabrales // Langmuir 25 (2009) 11078.
[82] Y.J. Shin, Y.Y. Wang, H. Huang, G. Kalon,
A.T.S. Wee, Z.X. Shen, C.S. Bhatia and
H. Yang // Langmuir 26 (2010) 3798.
[83] X. Feng and L. Jiang // Adv. Mater. 18 (2006)
3063.
[84] X. Li, W. Cai, J. An, S. Kim, J. Nah, D. Yang,
R. Piner, A. Velamakanni, I. Jung, E. Tutuc,
S.K. Banerjee, L. Colombo and R.S. Ruoff //
Science 324 (2009) 1312.
[85] Y. Zhou, Y. Jiang, T. Xie, H. Tai and G. Xie //
Sens. Actuators B 203 (2014) 135.
[86] J. Rafiee, X. Mi, H. Gullapalli, A.V. Thomas,
F. Yavari, Y. Shi, P.M. Ajayan and N.A.
Koratkar // Nat. Mater. 11 (2012) 217.
[87] C.-J. Shih, M.S. Strano and D. Blankschtein
// Nat. Mater. 12 (2013) 866.
[88] E. Sutter, P. Albrecht, F.E. Camino and
P. Sutter // Carbon 48 (2010) 4414.
[89] M. Batzill // Surf. Sci. Rep. 67 (2012) 83.
[90] D. Prasai, J.C. Tuberquia, R.R. Harl, G.K.
Jennings and K.I. Bolotin // ACS Nano
6 (2012) 1102.
[91] X. Zhang, S. Wan, J. Pu, L. Wang and X. Liu
// J. Mater. Chem. 21 (2011) 12251.
[92] J. Rafiee, M.A. Rafiee, Z.-Z. Yu and
N. Koratkar // Adv. Mater. 22 (2010) 2151.
[93] C.K. Wu, G.J. Wang and J.F. Dai // J. Mater.
Sci. 48 (2013) 3436.
[94] C. Van Oss, R. Good and M. Chaudhury //
Langmuir 4 (1988) 884.
71
[95] C.J. Van Oss, M.K. Chaudhury and R.J.
Good // Chem. Rev. 88 (1988) 927.
[96] F.M. Etzler, In: Contact Angle, Wettability
and Adhesion, ed. by K.L. Mittal (VSP,
Utrecht, 2003), p. 1.
[97] C. Della Volpe, D. Maniglio, M. Brugnara,
S. Siboni and M. Morra // J. Colloid Interface
Sci. 271 (2004) 434.
[98] S. Siboni, C. Della Volpe, D. Maniglio and
M. Brugnara // J. Colloid Interface Sci. 271
(2004) 454.
[99] J. Long, M. Hyder, R. Huang and P. Chen //
Adv. Colloid Interface Sci. 118 (2005) 173.
[100] A. Marmur // Soft Matter 2 (2006) 12.
[101] L. Lavielle and J. Schultz // Langmuir
7 (1991) 978.
[102] E. Papirer, E. Brendle, F. Ozil and H. Balard
// Carbon 37 (1999) 1265.
[103] X. Zhang, D. Yang, P. Xu, C. Wang and
Q. Du // Journal of Materials Science 42
(2007) 7069.
[104] R. Menzel, A. Lee, A. Bismarck and M.S.
Shaffer // Langmuir 25 (2009) 8340.
[105] R. Menzel, A. Bismarck and M.S. Shaffer //
Carbon 50 (2012) 3416.
[106] H.P. Schreiber and D.R. Lloy, In: Inverse
gas chromatography: characterization of
polymers and other materials (American
Chemical Society, Washington, DC, 1989),
p. 1.
[107] R. Menzel, A. Lee, A. Bismarck and M.S.P.
Shaffer // Langmuir 25 (2009) 8340.
O&.PD @Qj
Qb: QbY
S[~ D >eb
U [Q
A
S]Q 9 Cd
i
U [f
l
QV
l f
lQ T
M. Otyepka // JACS 135 (2013) 6372.
[109] J.F. Dai, G.J. Wang and C.K. Wu //
Chromatographia 77 (2014) 299.
[110] J.F. Dai, G.J. Wang, C.K. Wu and L. Ma //
J. Mater. Sci. (2014), in press.
O PA 5i
l JQb
UQ > DQb
UTUcG JYQbF TY
FFj
QTQ5 AQb
d
mUj5 c Q T>A 8
HQcSo %
%
Carbon 75 (2014) 390.
[112] Y. Hernandez, M. Lotya, D. Rickard, S.D.
Bergin and J.N. Coleman // Langmuir 26
(2010) 3208.