SURFACE PROPERTIES OF GRAPHENE: RELATIONSHIP TO … · the property of composites is determined mainly by the synergistic combination of high specific surface area of graphene, strong

60 J.-F. Dai, G.-J. Wang, L. Ma and Ch.-K. Wu

© 2015 Advanced Study Center Co. Ltd.

Rev. Adv. Mater. Sci. 40 (2015) 60-71

Corresponding author: Guo-Jjian Wang, e-mail: [email protected]

SURFACE PROPERTIES OF GRAPHENE: RELATIONSHIPTO GRAPHENE-POLYMER COMPOSITES

Jin-Feng Dai1, Guo-Jian Wang1,2, Lang Ma1 and Cheng-Ken Wu1

1School of Materials Science and Engineering, Tongji University, Shanghai 201804, China2Key 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 elec-tronic, optical, magnetic, thermal, and mechanical properties. Despite continuing theoretical andexperimental success, the unique physical properties of graphene remain underused andunderappreciated. The key challenge in harnessing of the unique properties of graphene is thedifficulty of reliable manipulation of well-dispersed graphene which due to the surface propertiesof graphene. In this review, the recent developments of surface properties of graphene aresummarized, where tailoring of these surface properties via surface treatments and the effectson the graphene-polymer matrix interface is highlighted. Moreover, the surface testing techniqueis also commented on briefly. We believe that the future prospects of research emphasis onpreparation of modified graphene with special surface properties which would lead to bettercomposites taking into account the desired cradle-to-grave lifecycle of reinforced materials withhigh performance. Finally, we expect that this review can contribute to a better knowledge of thephysicochemical surface properties of graphene.

1. INTRODUCTION

Graphene, a nanometer-thick two-dimensional ana-log of fullerenes and carbon nanotubes [1], has re-cently sparked great excitement in the scientificcommunity given its excellent mechanical, thermaland electronic properties [2]. In addition, as a flex-ible material with large specific surface area,graphene has shown to be an outstanding building-block [3,4]. Despite its short history, graphene hasrevealed various potential applications [5-9] in theconstruction of devices, sensors, transparent con-ductive films, and composites. However, practicalapplication of graphene requires its large scale pro-duction primarily [3,10].

Up until now, versatile methods have been de-veloped for preparation of graphene and its deriva-tives, such as mechanical exfoliation [1], epitaxialgrowth [11], chemical reduction [3], liquid phaseexfoliation [12], chemical vapor deposition (CVD)

[13], and organic synthesis [14]. The advances inpreparation of graphene [2] not only provide com-mercial access to lager-area samples, but also fur-ther promote the application of graphene mining.However, as-prepared graphene easily agglomerateirreversibly due to the large surface area and sur-face energy, which makes it difficult to disperse inmost of solvents [3,10] and increases the difficultyin application. To this end, a number of researchgroups [15-21] have produced the well-dispersedgraphene sheets in solvents with decorating surfac-tants or stabilizers through physical and chemicalmethods. Although functionalization of grapheneenables us to obtain isolated graphene with gooddispersibility, this processing may destroy theunique properties of graphene.

Actually, graphene composites, especially forpolymer matrix composites, are regarded as one ofthe most promising industrial products in many ap-

61Surface properties of graphene: relationship to graphene-polymer composites

plications [22]. For graphene-polymer composites,the property of composites is determined mainly bythe synergistic combination of high specific surfacearea of graphene, strong filler-matrix interfacial ad-hesion as well as the exceptional properties ofgraphene, and also by the essential properties ofthe matrix. Importantly, the performance of compos-ites can be maximized if an effective load transferfrom the matrix to the graphene is guaranteed, be-cause graphene share major portion of the load towhich the composites structure is subjected. Thisis made possible by ensuring appropriate interfa-cial adhesion or compatibility between the matrixand the graphene. The interfacial adhesion is deter-mined by matrix properties and surface propertiesof graphene [23], such as the total surface area ofgraphene available for contact with matrix molecules;surface roughness of graphene, which may allowfor mechanical interlocking; the chemistry structureand surface energy of graphene, which determinewhether the graphene will be wetted by the matrix,as well as by the surface functional groups for form-ing attractive interactions, in particular, chemicalbonds with matrices or polar interactions (such asLewis acid-base interactions and hydrogen bonds)with matrices [24]. Therefore, the surface proper-ties of graphene and surface/ interfacial interactionbetween graphene and matrix play crucial roles incontrol of the properties of composites. Furthermore,surface properties are especially important for hy-brid materials and coatings which are used in bio-medical, electronic and energy applications [25,26].

To best of our knowledge, surface properties andinterface energies are the most important physicalattributes of nanostructures [27,28] which are con-sidered as main factor affecting interfacial adhesionand surface processing of composites essentially[29,30]. Importantly, it has been realized that theanomalous surface energy of nanostructures alwaysinduces many novel phenomena which will requiresupporting of new technology and theory. Thus,considerable researches have been carried out onthe surface characterization and surface modifica-tions of graphene, which have been reviewed in moredetail in many literatures [31-33]. However, surfaceproperties of graphene as the most fundamental is-sue still has not been understood clearly. There-fore, it is necessary to realize and determine sur-face properties of graphene. In this review, we focuson surface properties of graphene which preparedfrom graphite oxide. Several recent reviews havealready addressed the synthesis, composites andfunctionalization of graphene. Hence, these will notbe discussed in detail here. We will survey for the

Fig. 1. (a) Schematic diagram of typical configura-tion of graphene; (b) TEM atomic resolution imageof graphene; (c) STM topographic image from asingle layer of graphene (adapted from ref. [34-36]).

status and progress of research of surface proper-ties of graphene, and aim to provide an overview ofthe different surface properties of graphene, for ex-ample, microstructure, surface area, surface chemi-cal composition, as well as surface energy, and thedetermination techniques of the surface propertiesof graphene. Moreover, tailoring of these surfaceproperties via surface treatments and the effects onthe graphene-polymer matrix interface are brieflydiscussed.

2. SURFACE STRUCTURE ANDMORPHOLOGY OF GRAPHENE

Surface properties of graphene are intimately relatedto the graphitic basal plane character of the graph-ite and can be illustrated in terms of the graphitestructure. Theoretically, the graphene honeycomblattice is composed of sp2 hybridization carbon at-oms bonded together with bonds. The remainingñ orbitals on each carbon ato] overlaps with thethree neighboring carbon atoms to form a orbitalthat contributes to a delocalized network of elec-trons. Based on microstructure analysis, the typi-cal configuration of single-layer graphene is not com-plete flat layer, but there are many initiative wrinklesand height fluctuations about ±0.5 n] on its sur-face, which has been demonstrated by Monte Carlosimulation [34], transmission electron microscopy(TEM) [35] and scanning tunneling microscopy(STM) [36], as shown in Fig. 1. Further, the correla-tion between fluctuations and electrical propertiesof graphene was studied exclusively by using STMtechnique [37,38]. Studies indicated that the change


Samples Preparation methods SBET

(m2·g-1) Ref.

RGO Reduced by hydrazine 320 [53]RGO Reduced by hydrazine hydrate 466 [54]Al-GN Reduced by aluminum power 365 [55]MEGN Microwave assisted exfoliation 463 [56]CMG Chemically modified and reduced graphene 705 [57]TEGN Low-temperature exfoliation under vaccum ~400 [58]TEGN Thermal exfoliation of GO at 1050 °C under Ar 650 [59]TEGN Thermal exfoliation of GO at 1050°C under Ar 600~700 [48,60]TEGN Thermal exfoliation of GO at 800 °C in H

2 stream 940 [61]

FGN Based on Ref. [56], with activation of KOH, 3100 [62]thermal exfoliation at 800°C under Ar

Table 1. Specific surface area (BET) of different graphene samples determined using N2 adsorption.

of local electrical properties is negligible or limitedwhen corrugations are under 0.5 nm in height,whereas strained graphene for bigger ripples (2~3nm in height) exhibit tunneling conductance [39,40].The altered electrical property of graphene with struc-tural adjustment is likely important for possible ap-plication in graphene devices [41].

Huge specific surface area is an important fea-ture of graphene that determines the interface inter-action between graphene and matrix in composites.N

2 adsorption is a commonly used analytical tech-

nique for the determination of the specific surfacearea of solid materials, and the data are usuallyanalyzed using the Brunauer-Emmett-Teller (BET)theory [42]. Until now, there have been several re-ports on specific surface area of graphene, a fewexamples were given in Table 1. Although the theo-retical specific surface area of graphene is 2630m2·g-1 [3], the as-prepared graphene samples (asmentioned in Table 1) have typical experimental val-ues of the specific surface area ranging from ~100to ~1000 m2·g-1, which is due to surface area ofgraphene depend strongly on their layers and struc-ture. The results further show that graphene manu-factured by thermal exfoliation at high temperaturehas more single-, few-layer structure, hence has

Fig. 2. SEM images of graphene composite: (a) EG-PMMA; (b) TEGN-PMMA (adapted from ref. [48]).

specific higher surface area. Besides, graphenetreated via chemical modification also can modu-late the surface area of graphene significantly tosome extent [43]. Improvement in the interfacial in-teraction or practical adhesion between thegraphene and polymer matrices/metal oxides hasbeen demonstrated by increasing the graphene sur-face area and surface roughness [3,44-47], whichcould be mainly attributed to mechanical interlock-ing and physical adsorption. For instance, PMMA-based nanocomposites filled with thermal exfoliatedgraphene sheets (TEGN) showed more superb ther-mal, mechanical, and rheological property than com-posites reinforced with expandable graphite (EG) atequivalent loading [48], and the images of electronmicroscope (as seen in Fig. 2) and experimentaldata suggested significant reinforcement from TEGNis attributed to strong interfacial interaction aug-mented by mechanical interlocking with the hostpolymer due to large surface area and wrinkledmorphology of the TEGN [48-50]. Aside from theeffect of roughness of graphene, Bruneton et al.[51,52] proposed that a strong adhesion requiredcarbon materials uniform occurrence of accessibleedges (which can be created by chemical surfacetreatments). Chemical surface treatments of


graphene do contribute to the performance of com-posites significantly. However, the surface functionalgroups introduced during the chemical surface treat-ments would change the surface chemical compo-sition of graphene, which will be discussed in thefollowing section.

3. SURFACE COMPOSITION ANDCHEMISTRY OF GRAPHENE

Pristine, ideal graphene is only a single layer ofcarbon atom with simplex sp2 hybridization. How-ever, reduced graphene obtained from the reductionof graphene oxide still has tiny oxygen-containinggroups on its surface. The presence of these func-tional groups changes graphene structure, thus in-fluences the properties of graphene. Consequently,study of the composition of graphene is a priorityduring any application fields. X-ray photoelectronspectroscopy (XPS) is a technique that allows thecomposition of the outermost few atomic layers ofsolid surface to be analyzed. It is commonly usedto characterize the surface composition of grapheneas well as the oxidation state of elements presentin the graphene surface by analyzing the chemicalshift of the atomic core level binding energies[32,63,64]. In Table 2, the surface composition oftypical graphene oxide (GO), chemical reducedgraphene (RGN), thermal exfoliation graphene(TEGN) and functionalized graphene (FGN) deter-mined by XPS is summarized. It is found that themain differences between the various graphenesamples are their carbon/oxygen ratios (C:O) anddegree of sp3 hybridization, which are related to thepreparation process and the surface treatment ofgraphene.

Although the pristine graphene has the highesttheoretical strength, its perfect honeycomb latticemakes graphene chemical inertness. As we known,the presence of functional groups on graphene sur-

Samples Treatment C:O ratio N(%) sp3 hybridization Ref.component (%)

GO Chemical Oxidation 1.9~2.8 0 ~70 [4,65,66]of graphite

RGN Reduced via 4~10.3 <3 ~27~13.5 [66-68]chemical methods

TEGN Thermal exfoliation of GO 5.6~10.0 0 ~18~14.7 [48,59,69]FGN 1. Treated via >246 <0.5 ~2 [62,70]

chemical methods;2. Thermal exfoliation

Table 2. Surface composition and C1s peaks of different graphene samples determined using XPS.

face can modifies its surface chemistry, even canbenefits dispersibility in some solvents and matrixes[71]. Bao et al. [66], Liang et al. [72], and Wang etal. [73] prepared GO/PVA composites by solutionprocessing method. The result shows that tensilestrength of the composites increases with the en-hancement of oxygen content of GO. The authorsascribed the result to two possible mechanisms.First, interfacial interactions between GO and PVAmatrix is thought to be controlled by chemical bond-ing between suitable functional groups presentedon graphene surfaces; and second, mechanical in-terlocking due to the enhanced nanoscale surfaceroughness that have been elaborated in this reviewpreviously. Whereas, the situation with RGO andTEGN is much different, the surface defects in car-bon lattice due to the severe oxidation process andpoor dispersion in polymer matrix due to the func-tional groups removal process have reverse effectson the performance of composites [72,74,75]. Evenif the mechanical property of RGO and TEGN ismuch higher than GO, the improvement of perfor-mance of composites is still relative small [66].

The interaction of graphene and polymer matrixat the interface has significant implications for thefinal composites properties. The tailoring of interfa-cial interaction and dispersion by functionalizationand modification between graphene and polymermatrix has been focused. The methods offunctionalization and modification of graphene havealready reported elsewhere. Hence, we will not re-peat again. A recent in-situ polymerization strategyhas been shown to provide strong interfacial inter-action and good dispersion between graphene andpolymer matrix directly [76]. The comparative stud-ies of both GO and modified graphene oxide (MGO)based polyimide (PI) nanocomposites were carriedout by Wang et al. [77] and Liao et al. [78]. Theirresults all reveal that MGO/PI composites exhibitgreater mechanical properties than that of GO/PI


Fig. 3. SEM images of fractured surface of GO/PI (a, b) and MGO/PI (c, d) composites; model of theinterphase structure of GO/PI (e) and MGO/PI (f) composites (adapted from ref. [77]).

composites. The enhancement to some extent ofthe mechanical properties of the composites wasascribed to better homogeneous dispersion of MGOin the matrix than that of GO/PI composites, aswell as strong interfacial interactions between bothcomponents (as shown in Figs. 3a-3d). In order toexplain this phenomenon accurately, the authorssimulated the process (as depicted in Figs. 3e-3f),suggesting that graphene surface modified by poly-mer vary the surface composition and surface prop-erties of graphene, thus form a flexible interphasebetween polymer and graphene to provide an effec-tive path for load transfer.

4. WETTABILITY OF GRAPHENE

The interaction between a liquid and graphene sur-face is manifested in the wettability of graphene,which has attracted more and more interests in thefield of surface chemistry, physics, and materialsscience because it may have lots of practical appli-cation [26,79]. However, quantitative knowledge ofwetting properties of graphene is still lacking. Ex-perimentally, the wettability of graphene is com-monly quantified by measuring contact angles (CA,). When a liquid drop is placed on a flat solid sub-

strate, it either spreads into a thin continuous filmor beads up. The is defined as the angle at whicha liquid-vapor interface meets the solid surface. Evenif graphene has already been recognized as a hy-drophobic material [80], extensive works are stillongoing for better understanding the wetting prop-erties of graphene.

Recently, Wang et al. [81] reported that the wa-ter contact angle of graphene films produced by

chemical exfoliation (127.0°) is much higher thanthat of graphite (98.3°). While Shin et al. [82] pre-pared single-, bi-, and multi-layer graphene by epi-taxial method which have similar water contact angleto graphite (~92°). Interestingly, these two contra-dictory results are supported by consistent evidencefrom water contact angle measurements. It can beascribed to different roughness of the testedsamples. Obviously, the irregularly stacked graphenefilms comprised microstructure and nanostructure(as shown in Fig. 4), which enhanced the CA andhydrophobicity of graphene [83]. Although bothgraphene film and graphene layer are the same kindof material, their wettability is changed with theirdifferent surface morphology. As a result, thewettability of both graphene film and graphene sheetshould be further discussed respectively.For the graphene layer, Shin‘s report [82] sug-

gested that there is no thickness dependence ofthe CA of water from measurements on single-, bi-and multi-layer graphene coated on SiC. However,Rafiee‘s study revealed that there are different CAon different layers of graphene sheets dependingon the type of substrate [86]. In their experiment, aseries of different layers of graphene sheet was pre-pared on Cu substrate using CVD method, and thenwas transferred onto Si, Au, and glass substrates,respectively. As shown in Fig. 5, the measurementresults of CA showed that graphene is wetting trans-parent for Cu substrate but not for glass, when thelayer of graphene is less than 4. Beyond fourgraphene layers there is a relatively sharp increasein the CA value. Finally, with increase of layers ofgraphene, especially when it is more than 6, the CA


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 fromref. [86]).

value of graphene tends to be stable and achievethe CA value of the graphite. Subsequently, the sameresults of wetting experiments were also obtainedby performing on Si and Au substrates. Moleculardynamics simulations and theoretical predictionsfurther confirm that wettability of graphene layer isrelated to thickness of graphene and nature of sub-strates. Because the CA on hydrophilic substrate(such as glass) is dominated by short-range chemicalforces, the presence of graphene between hydro-philic substrate and water will significantly disruptthe chemical bonding at their interface. However,the CA on the hydrophobic surface (such as Cu, Si,and Au) is dominated by the relatively long-rangevan der Waals interactions, and is maintained forless than four graphene layers. This conclusion wasfurther reported by Shin et al. [87] thoroughly. Theypointed out that a single layer graphene becomesmore transparent for wetting on hydrophilic sub-strates and more opaque for wetting on hydropho-

bic substrates. The finding also implies thatgraphene layer can be used as an ideal material forprotecting reactive substrate surfaces without chang-ing wetting properties of substrate materials [88-90].

In addition, the wetting behavior of graphenesheet not only depends on the layer numbers ofgraphene and the substrates for preparation ofgraphene, but also on the surface chemical compo-sition of graphene. Shin et al. [82] studied the wet-ting behavior of various modified graphene and foundthat their wettability is related to the oxygen-con-taining groups and even can be modulated by opti-mized chemical surface treatments technology (CAin water, as shown in Table 3). Furthermore, chemi-cal surface treatments of graphene show much moreintense influences on wettability of graphene thanvariation layer of graphene at the same substrate.

In the present study, for the graphene film, it al-ways shows highly hydrophobic behavior due to


microstructure and nanostructure surface roughness[82,91]. Zhang et al. [91] performed the experimentson the correlation of the CA with the centrifugalspeeds (as shown in Fig. 6a). It was found that thehydrophobicity of the graphene film is governed andmodulated by the morphology of film, especially bymicrostructure of film, and is hardly influenced bylayer numbers of graphene and the substrates forpreparation of graphene. Consequently, there ismany potential controllable manipulation of the wet-ting action of the graphene film. As mentioned above,chemical surface treatment of graphene has signifi-cantly influence on wettability of graphene. It meansthat this method also has similar effects onwettability of graphene film, because of the graphene

Sample Single- Bi- Multi- O2 Plasma One day after Annealed

graphene graphene graphene treated plasma treated

/ ° 92.5 91.9 92.7 55.1 72.4 87.3

The data were adapted from ref. [82]

Table 3. The contact angle ( ) of sample to water.

Fig. 6. (a) CA of graphene films by different centrifugal speeds, inset: SEM images of the correspondingfilms by different centrifugal speeds; (b) The relationship between the CA of the graphene film and itsexposure time in air; (c) The reversible wettability transition of graphene film by exposure in UV irradiationand in air (adapted from ref. [91]).

films always comprising the graphene layer. Basedon the experiment of relationship between the mor-phology and the hydrophobicity of graphene film,Zhang et al. [91] further reported the tunablewettability of graphene film by interaction with etha-nol, showing that the wettability of graphene filmcan be reversibly modified through exposure in airand UV irradiation (from hydrophilic tosuperhydrophobic, again to hydrophilic, as seen inFigs. 6b and 6c). The authors ascribed the resultsto the adsorption and desorption of water and oxy-gen molecules on the graphene surface. Obviously,the adsorption and desorption process significantlyaffect the surface components and surface ener-gies of graphene film. Therefore, the wetting behav-


ior of graphene film also varies with the conversionof the adsorption and desorption process. Rafiee etal. [92] reported functional graphene film that thewetting behavior of film can be tailored over a widerange (from superhydrophobic to superhydrophilic)by controlling relative proportion of acetone and waterin preparation process. These results demonstratethat the surface chemistry of graphene is very im-portant to alter the wettability of graphene essen-tially. Very recently, our group [93] also studied therelationship between proportion of solvent and sur-face composition of graphene oxide film. It was foundthat the solvent with carbonyl group can adsorb onthe surface of the graphene oxide film. Therefore,the roughness and surface chemistry of grapheneare changed obviously which lead to the variation ofwetting behavior.

With all of the above results, we suggest thatthe role of chemical heterogeneities on the graphenesurface has very important influence for the wettingproperties of graphene.

5. SURFACE ENERGY OF GRAPHENE

The investigation of the surface energy of grapheneis of great importance, because it strongly influencesthe wettability of graphene and the formation of thegraphene-based composites interface. The surfaceenergy of graphene can be determined from themeasurement of contact angles of suitable test liq-uids on graphene surface using different surfaceenergy models following essentially two approaches:1) the equation of state approach and 2) the surfaceenergy component approach [94,95]. While theequation of state approach only provides the solidsurface energy, the various surface energy compo-nent approaches can provide further information,such as dispersive and non-dispersive componentof graphene, including polar or acid-base compo-nents. Further details of these models can be foundin others‘ reviews [96-98]. Based on these ]odels,Wang et al. [81] employed contact angle method toobtained surface free energy of RGO, GO, and graph-ite, and found that the surface free energy of themis 46.7 ]>·]-2, 62.1 ]>·]-2,and 54.8 ]>·]-2, re-spectively. This study indicates that oxidative sur-face modification considerably increased the sur-face energy. On the other hand, reducing materialdimension from 3D to 2D may reduce the wettabilityand decrease the interfacial adhesion with liquids.However, Shin et al.[87] calculated the surface en-ergy of monolayer, bi-layer, and tri-layer grapheneby assuming a continuous distribution of carbonatoms and using a Lennard-Jones carbon-carbon

potential, and found that it is much higher than thatof Wang‘s work [81]. It de]onstrates that the re-sults of surface energy obtained from CA may beseverely flawed for the graphene surface character.Moreover, Raj et al. [79] further pointed out that staticcontact angle measurements for wettability andsurface energy of graphene cannot solely be usedon such rough, defective and chemical heteroge-neous surface. The presence of chemical inhomo-geneity and the surface roughness of graphene makethe contact angle measurements less appropriatefor evaluation of surface energies [99]. In fact, it hasbeen reported that methods based on contact anglemeasurements can influenced the facticity of thetest results, particularly those concerning acid-basecharacteristic of the surface of the materials [100].

Inverse gas chromatography (IGC) is also usedto investigate the surface energies of carbon mate-rials [101-105], such as carbon nanotubes, carbonfibers, and carbon black. In the IGC experiment,carbon materials are used as the stationary phase,and a mobile gas or vapor phase with well-knownproperties is injected as a probe into the columnfilled with carbon material at a fixed carrier gas flowrate. It is noted that this efficient and sensitive tech-nique requires only a small amount of sample fordetermination of surface energy. Moreover, severalthermodynamic quantities (i.e. free energy of ad-sorption and enthalpy of adsorption), the polar com-ponents of surface energy and acid-base propertiesof the materials can also be ascertained easily us-ing IGC technique [106]. Recently, Shaffer et al.[107] achieved the surface properties of as-receivedand modified carbon nanotubes (CNTs) using IGC,and obtained a series of thermodynamic surfaceparameters (such as dispersive surface energies,specific surface energies, electron acceptor (K

A) and

donor (KD) numbers, and adsorption capacities). In

addition, Shaffer‘s group[105] further realized thedeconvolution of contributions of structural andchemical surface energies of CNTs by IGC withbranched probes, and given out that the specificsurface energies is depended on the modificationtreatment markedly. Inspired by these works, IGCis also adopted to determine the thermodynamicsurface properties of graphene. In a more recentstudy by Otyepka et al. [108] the adsorption en-thalpies of organic molecules on graphene weredeter]ined using IGC and ranged fro] -5.9 kcal·mol-1 for dichloro]ethane to -13.5 kcal·]ol-1 for tolu-ene. Otyepka et al. concluded that organic mol-ecules can adsorb on graphene surface is due tothe interaction energy and specific surface energyof graphene. Different fro] Otyepka‘s work, our


Samples d

s ]>·]-2) p

s ]>·]-2) - Gsp

DCM k>·]ol-1) - Gsp

EtAc k>·]ol-1) K

AK

D

GO 78.9±3.1 57.1±3.3 5.13 12.1 0.35 0.66COOH-GO 83.3±4.2 81.2±3.5 5.84 15.2 0.52 0.95EG-RGO 92.8±4.1 37.3±3.1 3.89 10.4 0.30 0.49RGO 106.8±5.3 8.05±1.4 1.66 5.29 0.29 0.35Graphite 124.6±3.8 3.96±1.0 0.75 5.78 0.28 0.18

The data adapted from ref. [109,110]

Table 4. Thermodynamic surface properties of graphite, GO, RGO, EG-RGO, and COOH-GO at 40°C.

group [109,110] further studied the thermodynamicsurface properties of graphite, graphene oxide (GO),reduced graphene oxide (RGO), ethylene glycol-treated graphene oxide (EG-RGO), and carboxy-lated graphene oxide (COOH-GO) using IGC. Thedata of thermodynamic surface parameters weresummarized in Table 4. The results showed thatthe decrease of oxygen-containing groups of mate-rials reduce the polar component while increase thedispersive surface energies, which may be attrib-uted to the change of polar functional groups andlocal defects. In Table 4, the acid-base characteris-tic of the as-prepared materials was also listed. Itwas found that K

D is bigger than K

A indicative of a

Lewis-base surface for GO. As the same, the sur-face character of the other as-prepared materialswas also characterized: COOH-GO exhibits Lewis-base character, EG-RGO, and RGO both showamphoteric but more Lewis-base character, whilegraphite reveals Lewis-acid character. Consequently,it can be concluded that the type and amount ofdefects and functional groups on the surface ofgraphene would alter the surface properties ofgraphene as well as Lewis acid-base surface char-acter of graphene. Combined with the results ofenhanced mechanical properties of graphene-basednanocomposites [66,73,77,78] as mentioned in sec-tion two, it reveals that any surface treatments tomodify surface chemistry of graphene could lead tothe decrease of dispersive surface energy whilstchange of surface character of Lewis acid-base,which will make better interfacial interaction anddispersion between graphene and different polymers.Therefore, both surface energy and surface charac-ter of Lewis acid-base could be fast and useful mea-surement parameters for analyzing surface treat-ment. Moreover, determination of surface energiesof graphene can also help to establish Hansen-likesolubility parameters of graphene [110-112], forchoosing suitable solvents to improve dispersion ofgraphene theoretically. As a result, evaluation ofsurface energies and surface character of Lewis acid-

base of graphene would facilitate preparation ofgraphene-polymer composites and development ofgraphene-based materials.

6. CONCLUSION

Graphene is considered as one of the best rein-forcements for composite materials. Currently, thedevelopment of graphene-based nanocompositeswith enhanced mechanical properties and additionalfunctionality (thermal, electrical, and optical prop-erties, etc.) is ongoing. In order to fully utilize theadvantages of graphene, a comprehensive under-standing of graphene surface properties is crucial,as they determine the interfacial adhesion and com-patibility at graphene-matrix interface and the over-all composite performance. This review endeavorsto sum up the current research status on surfaceproperties of graphene that have predominated inthe application field of graphene-based composites.The influence factors of surface properties ofgraphene, such like microstructure, surface area,surface chemistry and composition, as well as sur-face energy, and the techniques that can be usedto determine the surface properties of graphene werediscussed. The conclusion indicated that to tailorthe surface properties of graphene by modificationof graphene surface chemistry is essential to re-ceive a better compatible composite which can im-proves the interfacial interaction via 1) mechanicalinterlocking by increasing surface area and wrinkle,2) chemical bonding by functional groups ongraphene surface, such as van der Waals and hy-drogen bonding, which also leads to the decreaseof the dispersive surface energy of graphene whilstthe improvement of wettability of the graphene forthe matrix. With no doubt, further developments insurface characterization techniques and graphenesurface treatments will lead to improved understand-ing of the surface properties of graphene and bettercontrol of interfacial properties in composites. In thisway, evaluation of surface properties of graphene is


desirable, which would be used to guide the pro-cessing and application in graphene-basednanocomposites 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 // Nature442 (2006) 282.

[4] O.C. Compton and S.T. Nguyen // Small6 (2010) 711-723.

[5] Y. Sui and J. Appenzeller // Nano Lett.9 (2009) 2973..

[6] C. Shan, H. Yang, J. Song, D. Han, A. Ivaskaand 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 Nano4 (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 andD. 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 andD. Zhu // Adv. Mater. 20 (2008) 3289.

[14] >. Wu, W. Pisula and K. Müllen // 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.

[21] Y. Hernandez, V. Nicolosi, M. Lotya, F.M.Blighe, Z. Sun, S. De, I.T. McGovern,B. Holland, M. Byrne, Y.K. Gun’Ko, >.>.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 // Carbon63 (2013) 9.

[23] J. Du and H.-M. Cheng // MacromolecularChemistry and Physics 213 (2012) 1060.

[24] M. Peressi, Surface Functionalization ofGraphene. In: Graphene Chemistry, (JohnWiley & Sons, Ltd, 2013) p. 233.

[25] H. Chen, M.B. Müller, K.>. Gil]ore, G.G.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 InterfaceSci. 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 // ChemicalReviews 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 Reviews112 (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 // Nature446 (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. Lauand B.J. LeRoy // Phys. Rev. B 79 (2009)205411.

[38] Y. Zhang, V.W. Brar, C. Girit, A. Zettl andM.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.


[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 // NatNano 4 (2009) 56.

[42] M. Tho]]es, R. Köhn and M. Fröba //J. Phys. Chem. B 104 (2000) 7932.

[43] Q. Tang, Z. Zhou and Z. Chen // Nanoscale5 (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 andZ. Liu // Polym.-Plast. Technol. Eng. 51(2012) 251.

[46] C.N.R. Rao, A.K. Sood, K.S. Subrahmanyamand 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.Prud’Ho]]e and L.C. Brinson // 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 // Polymer50 (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. C113 (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 andB. 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,R.K. Prud’ho]]e, R. Car, D.A. Saville and

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. Herrera-Alonso, D.L. Milius, R. Car, R.K.Prud’ho]]e and I.A. Aksay // Chem. Mater.19 (2007) 4396.

[61] K. Evanoff, A. Magasinski, J. Yang andG. Yushin // Advanced Energy Materials1 (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 // Science332 (2011) 1537.

[63] S. Pei and H.-M. Cheng // Carbon 50 (2011)3210.

[64] D.R. Dreyer, S. Park, C.W. Bielawski andR.S. Ruoff // Chemical Society Reviews 39(2010) 228.

[65] A. Ganguly, S. Sharma, P. Papakonstantinouand 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. Solis-Fernandez, A. Martinez-Alonso andJ. 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. Jiangand 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. Martnez-Alonso 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 andX. Shang // Polym. Int. 60 (2011) 816.

[74] H. Kim and C.W. Macosko //Macromolecules 41 (2008) 3317.

[75] C. Goě]ez-Navarro, >.C. Meyer, R.S.Sundaram, A. Chuvilin, S. Kurasch,M. Burghard, K. Kern and U. Kaiser // NanoLett. 10 (2010) 1144.

[76] V. Singh, D. Joung, L. Zhai, S. Das, S.I.Khondaker and S. Seal // Progress inmaterials science 56 (2011) 1178.


[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 // NanoLett. 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 andL. 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 andH. 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 andP. 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 Nano6 (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 andN. 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.

[95] C.J. Van Oss, M.K. Chaudhury and R.J.Good // Chem. Rev. 88 (1988) 927.

[96] F.M. Etzler, In: Contact Angle, Wettabilityand 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 InterfaceSci. 271 (2004) 434.

[98] S. Siboni, C. Della Volpe, D. Maniglio andM. 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: Inversegas chromatography: characterization ofpolymers and other materials (AmericanChemical Society, Washington, DC, 1989),p. 1.

[107] R. Menzel, A. Lee, A. Bismarck and M.S.P.Shaffer // Langmuir 25 (2009) 8340.

[108] P. Lazar, F. Karlick~, P. >urečka,M. Koc]an, E. Otyepková, K. Šafářová andM. 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.

[111] M. Ayán-Varela, >.I. Paredes, S. Villar-Rodil,R. Rozada, A. Martínez-Alonso and >.M.D.Tascón // Carbon 75 (2014) 390.

[112] Y. Hernandez, M. Lotya, D. Rickard, S.D.Bergin and J.N. Coleman // Langmuir 26(2010) 3208.

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SURFACE PROPERTIES OF GRAPHENE: RELATIONSHIP TO … · the property of composites is determined mainly by the synergistic combination of high specific surface area of graphene, strong