Effect of flake size on thermal properties of graphene oxide/poly(methyl methacrylate) composites prepared via in situ polymerization

The effect of graphene oxide (GO) flake size on thermal properties of GO/poly(methyl methacrylate) (GO/PMMA) composites prepared via in situ polymerization was investigated. Two styles of GO sheets were synthesized from different sizes of graphite powders by modified Hummers' method and GO/PMMA composites with GO of different sizes were prepared via in situ polymerization. Transmission electron microscopy verified that GO sheets produced from large graphite powders was obviously larger than that from small graphite powders. The similar number of layers and disorder degree of two types of GO sheets were proved by X‐ray diffraction and Raman, respectively. X‐ray diffraction and scanning electron microscopy results of GO/composites proved the homogenous dispersion of both two types of GO sheets in polymer matrix. Dynamic mechanical analysis and thermogravimetric analysis results showed that large GO sheets exhibit better improvement than small GO sheets in thermal properties of the composites. Compared with neat PMMA, the glass transition temperature and decomposition temperature of the composites with large GO sheets (0.20 wt %) were increased by 15.9 and 25.9 °C, respectively. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46290.     

Fabrication of polymer/microwave‐reduced graphite oxide nanocomposites by ball‐milling assisted wet compounding

Microwave‐induced reduction of graphite oxide (GO) is a promising method for rapid and scalable production of graphene. However, homogeneous incorporation of thus prepared graphene into polymer matrix is still a hard task. In this article, we present a ball‐milling assisted wet compounding method for the fabrications of microwave‐reduced GO (MRGO)/polymer composites. MRGO powders were added into a solution of polystyrene (PS) and then mechanically exfoliated in a stirring mill. Scanning electron microscopy and transmission electron microscopy investigations show that the graphene sheets have been homogeneously dispersed in the PS matrix. The composites show pronouncedly improved properties. The thermal degradation temperature of composites increased by 34°C with the addition of 5wt% MRGO in PS. Up to 76% improvement of storage modulus (at 30°C) is achieved by compounding with 10wt% MRGO.POLYM. COMPOS., 2013. © 2013 Society of Plastics Engineers     

高电活性石墨烯/聚苯胺纳米复合材料的制备和表征

采用了一种简单有效地方法制备了高电活性的石墨烯/聚苯胺复合材料。首先,将苯胺在氧化石墨烯（GO）的水性分散液中氧化聚合,制备了氧化石墨烯/聚苯胺（GO/PANI）,再将GO/PANI与水合肼反应,制得还原-氧化石墨烯/聚苯胺（R（GO/PANI））。利用透射电子显微镜（TEM）,热失重分析（TGA）和循环伏安法（CV）对GO/PANI和R（GO/PANI的形貌,热稳定性和电化学性能进行了分析研究。结果表明,GO表面存PANI,且R（GO/PANI）的热稳定性和电活性都明显高于GO/PANI。     

Graphene/nanosized silicon composites for lithium battery anodes with improved cycling stability

Graphene/nanosized silicon composites were prepared and used for lithium battery anodes. Two types of graphene samples were used and their composites with nanosized silicon were prepared in different ways. In the first method, graphene oxide (GO) and nanosized silicon particles were homogeneously mixed in aqueous solution and then the dry samples were annealed at 500 °C to give thermally reduced GO and nanosized silicon composites. In the second method, the graphene sample was prepared by fast heat treatment of expandable graphite at 1050 °C and the graphene/nanosized silicon composites were then prepared by mechanical blending. In both cases, homogeneous composites were formed and the presence of graphene in the composites has been proved to effectively enhance the cycling stability of silicon anode in the lithium-ion batteries. The significant enhancement on cycling stability could be ascribed to the high conductivity of the graphene materials and absorption of volume changes of silicon by graphene sheets during the lithiation/delithiation process. In particular, the composites using thermally expanded graphite exhibited not only more excellent cycling performance, but also higher specific capacity of 2753 mAh/g because the graphene sheets prepared by this method have fewer structural defects than thermally reduced GO.     

Improvement of mechanical properties of graphene oxide/poly(allylamine) composites by chemical crosslinking

Graphite oxide was prepared by oxidation of graphite using the Hummers method, and its ultrasonication in water yielded dispersed graphene oxide (GO) sheets. These sheets were then crosslinked with a water soluble polymer, namely poly (allylamine) hydrochloride (PAH), by carbodiimide coupling. Free standing composite films were obtained by filtration. These crosslinked composites showed better mechanical properties than unmodified GO films and those of composites that were made by simple mixing of GO and PAH. The filtration process was optimized to produce strong GO films which were subsequently crosslinked with PAH in-situ to produce very strong composites with tensile strengths up to146 MPa.     

水辅混炼挤出聚苯乙烯/氧化石墨烯纳米复合材料的微观结构及流变与热性能

采用自主设计的水辅混炼挤出设备,制备3种氧化石墨烯（GO）含量（0.1 %、0.3 %、0.5 %,质量分数,下同）的聚苯乙烯（PS）/GO纳米复合材料,观察样品的微观结构,测试其流变性能和热性能。结果表明,GO被较好剥离且呈网状较均匀地分散在PS基体中,这主要归因于螺杆混炼流场不断细化PS熔体中的GO悬浮液以及水对熔体的塑化和溶胀效应促进PS分子链插层进入GO片层之间的共同作用;低频区PS/GO样品的储能模量、复数黏度和松弛时间均比纯PS样品的高,这是因为较均匀分散的网状GO片与PS之间形成较强的分子间作用力,降低了PS分子链的活动性;PS/GO样品的热稳定性比纯PS样品的高,这归因于GO片在PS基体中呈网状分布和GO表面存在π键。     

Preparation and properties of reduced graphene oxide/fused silica composites

An in situ strategy for fabrication of reduced graphene oxide/fused silica (rGO/FS) composites using 3-aminopropyltriethoxysilane as surfactant is reported. GO nanosheets were bound to FS particles by an electrostatic assembly between ultra thin negatively charged GO sheets and positively charged amino-modified FS particles. After spark plasma sintering, rGO/FS bulk composites have been produced from the GO and FS composite particles with GO being reduced to rGO in vacuum at high temperatures. Results show that rGO sheets were well dispersed in the matrix, and conductivity of these rGO/FS composites at room temperature was strongly dependent on the rGO nanosheet concentration. i.e., the conductivity of rGO/FS was increased to 10⁻⁴ S/cm when a conducting network was formed inside the composites. The effect of GO nanosheets on the mechanical properties of rGO/FS bulk composites was also investigated. The addition of 1 wt.% GO sheets to FS resulted in 72% increase in Vickers hardness, indicating the stress transfering from the FS matrix to the rigid rGO sheets. With the same rGO content, the fracture toughness of the as-prepared composites was increased by 74%. The main toughening mechanisms were thought to be crack deflection, crack branching, pulling-out and bridging of the rGO sheets.     

Preparation of graphene oxide/natural rubber composites by latex cocoagulation: Relationship between microstructure and reinforcement

Graphene oxide(GO) has recently attracted substantial interest as a possible reinforcing agent for next generation rubber composite materials. In this research, GO was incorporated in natural rubber(NR) composites through latex co-coagulation technique. The microstructures of GO/NR composites were characterized through a combination of transmission electron microscope, scanning electron microscope, X-ray diffraction, Fourier transform infrared spectroscopy, and Differential scanning calorimeter. The results showed that highly exfoliated GO sheets were finely dispersed into NR rubber matrix with strong interface interaction between GO and NR. The mechanical properties of the GO/NR composites were further evaluated. The results showed that the tensile strength, tear strength and modulus can be significantly improved at a content of less than 2 phr. Especially,GO exhibited specific reinforce mechanism in NR due to the stress-induced crystallization effects of NR. The stress transfer from the NR to the GO sheets and the hindrance of GO sheets to the stress-induced crystallization of NR were further displayed in stress–strain behavior of GO/NR composites. These enhanced properties were attributed to the high surface area of GO sheets and highly exfoliated microstructures of GO sheets in NR.     

Preparation of Pt Ag alloy nanoisland/graphene hybrid composites and its high stability and catalytic activity in methanol electro-oxidation

In this article, PtAg alloy nanoislands/graphene hybrid composites were prepared based on the self-organization of Au@PtAg nanorods on graphene sheets. Graphite oxides (GO) were prepared and separated to individual sheets using Hummer's method. Graphene nano-sheets were prepared by chemical reduction with hydrazine. The prepared PtAg alloy nanomaterial and the hybrid composites with graphene were characterized by SEM, TEM, and zeta potential measurements. It is confirmed that the prepared Au@PtAg alloy nanorods/graphene hybrid composites own good catalytic function for methanol electro-oxidation by cyclic voltammograms measurements, and exhibited higher catalytic activity and more stability than pure Au@Pt nanorods and Au@AgPt alloy nanorods. In conclusion, the prepared PtAg alloy nanoislands/graphene hybrid composites own high stability and catalytic activity in methanol electro-oxidation, so that it is one kind of high-performance catalyst, and has great potential in applications such as methanol fuel cells in near future.     

Graphene oxide/polybenzimidazole composites fabricated by a solvent-exchange method

Homogenous organic dispersion of graphene oxide (GO) sheets was prepared by a solvent-exchange method. This method enabled the simultaneous achievement of full exfoliation and high concentration of GO in several organic solvents such as dimethyl sulfoxide, which would facilitate the fabrication of individual graphene reinforced polymer composites through a solution-based process. To this end, poly [2,2′-(p-oxydiphenylene)-5,5′-bibenzimidazole] (OPBI)/GO composites were fabricated. X-ray diffraction characterization showed that the GO sheets were individually incorporated into the OPBI matrix. Scanning electron microscope images that taken of the fracture surface of the composites revealed that the GO sheets were spontaneous aligned parallel to the surface of the composite films as the content of GO exceeded 0.3 wt.%. The incorporation of GO also showed profound effects on the macroscopic properties of OPBI. Compared to pure OPBI, the composites showed a 17% increase in Young’s modulus, 33% increase in tensile strength and 88% improvement in toughness by the addition of only 0.3 wt.% of GO. Moreover, although the thermal stability of GO is far inferior to OPBI, it is found the thermal stability of OPBI is still improved by the addition of GO.     

Photoelectrochemical and electrochromic properties of polyimide/graphene oxide composites

A series of novel multicolored near-infrared electrochromic polyimide (PI)-based composites with graphene oxide (GO) were prepared by using in situ polymerization. The prepared PI/GO composites are readily soluble in many organic solvents, and display outstanding thermal resistance, stably electrochromic characteristics, high coloration efficiency, short switching time, and anodic electrochromic behavior. Scanning electron microscope and transmission electron microscopy showed a good and uniform dispersion of the GO sheets in the PI matrix. The surface of the composites contains hydrophilic functional groups such as C–O and CO, which have been characterized by X-ray photoelectron spectroscopy. The typical, stable photoelectrical response showed that there was electron transfer in the interior of composites film under illumination, and the electrochemical impedance spectra result was consistent with the photoelectrical response. The different content of GO played a pivotal role in the electron transfer and regulated the conductivity of the composites. The work functions were obtained by KPFM measurements, and the work function is increasing with the contents increasing of GO in the composites. The properties prove that the composite is multipurpose material which will cater for photoelectric conversion and electrochromic application.     

Synthesis of manganese (IV) oxide at activated carbon on reduced graphene oxide sheets via laser irradiation technique for organic binder-free electrodes in flexible supercapacitors

We report a novel, green, scalable technique to synthesize binder-free, high-purity conductive composite comprising activated carbon (AC), manganese dioxide nanorods (MnO₂), and reduced graphene oxide sheets (rGO) for flexible supercapacitors with outstanding electrochemical performance. UV pulsed laser irradiation of GO-based composite dispersion (AC/GO or MnO₂@AC/GO) in ethanol aqueous medium was used to induce a photocatalytic reduction of GO and simultaneous anchor AC particles or AC loaded MnO₂ nanorods (MnO₂@AC) on the reduced GO sheets (rGO) at room temperature and atmospheric pressure. rGO sheets serve as a large surface area, conductive binder to enhance the ion adsorption, electrical conductivity, and mechanical flexibility of supercapacitor electrodes. This laser-induced photocatalytic reduction method was used to prepare two different rGO-based colloidal composites AC/rGO (CG) and MnO₂@AC/rGO (MCG). The prepared rGO-based colloidal composites were used to fabricate symmetric supercapacitors (CG//CG and MCG//MCG) and asymmetric supercapacitors (MCG//CG) in which MCG is the positive electrode and CG is the negative one. All prepared rGO-based supercapacitors demonstrated significant improvement in their electrochemical performance compared with rGO-free AC based supercapacitors. The enhancement in the electrochemical properties of rGO-based supercapacitors could be attributed to the intrinsic characteristics of rGO, such as high surface area, excellent electrical conductivity, and super mechanical flexibility. Our approach is a one-step, scalable, cost-effective synthesis technique to produce all binder-free AC/rGO based composites for flexible energy-storage devices.     

Grafting of epoxy chains onto graphene oxide for epoxy composites with improved mechanical and thermal properties

Epoxy composites filled with both graphene oxide (GO) and diglycidyl ether of bisphenol-A functionalized GO (DGEBA–f–GO) sheets were prepared at different filler loading levels. The correlations between surface modification, morphology, dispersion/exfoliation and interfacial interaction of sheets and the corresponding mechanical and thermal properties of the composites were systematically investigated. The surface functionalization of DGEBA layer was found to effectively improve the compatibility and dispersion of GO sheets in epoxy matrix. The tensile test indicated that the DGEBA–f–GO/epoxy composites showed higher tensile modulus and strength than either the neat epoxy or the GO/epoxy composites. For epoxy composite with 0.25 wt% DGEBA–f–GO, the tensile modulus and strength increased from 3.15 ± 0.11 to 3.56 ± 0.08 GPa (∼13%) and 52.98 ± 5.82 to 92.94 ± 5.03 MPa (∼75%), respectively, compared to the neat epoxy resin. Furthermore, enhanced quasi-static fracture toughness (K_IC) was measured in case of the surface functionalization. The GO and DGEBA–f–GO at 0.25 wt% loading produced ∼26% and ∼41% improvements in K_IC values of epoxy composites, respectively. Fracture surface analysis revealed improved interfacial interaction between DGEBA–f–GO and matrix. Moreover, increased glass transition temperature and thermal stability of the DGEBA–f–GO/epoxy composites were also observed in the dynamic mechanical properties and thermo-gravimetric analysis compared to those of the GO/epoxy composites.     

GS改性氧化石墨烯/聚苯胺防腐材料的制备及性能

用双子表面活性剂(GS)通过静电作用对氧化石墨烯(GO)进行插层改性制备了改性氧化石墨烯(GSGO),再以苯胺(An)为单体,过硫酸铵(APS)为引发剂,通过原位聚合法制备了GSGO/PANI复合材料。最后利用GSGO/PANI与水性醇酸树脂(WAR)共混得到了GSGO/PANI/WAR防腐涂层。采用FTIR,Raman,XRD和SEM等测试手段对GSGO和复合材料的形貌、结构进行了表征,结果表明,GS插入到GO的片层中,使得GSGO的层间距增大,且棒状的聚苯胺分散在GO的片层中,形成片状插层结构。动电位极化和电化学阻抗谱测试表明,GSGO/PANI/WAR 复合涂层比纯WAR涂层具有更高的耐腐蚀性能。当复合涂层中w(GSGO)=10% 时,涂层的耐腐蚀性能最好。腐蚀电流密度从9.82?10-6A/cm2减小至1.08?10-6A/cm2,腐蚀电从-0.56V增加到-0.28V,|Z|值可达到5.25?106 ohm.cm2。     

“Clicking” graphite oxide sheets with well-defined polystyrenes: A new Strategy to control the layer thickness

Polystyrene (PS) graft graphite oxide (GO) was synthesized by Cu (I)-catalyzed 1, 3-dipolar cycloaddition (“click” coupling) of azido modified graphite oxide with well-defined, alkyne-terminated polystyrene. This method produced PS blocks graft on GO surface, while ordered layer structure between GO sheets was observed for the first time in GO/Polymer composite. The layered structure was characterized and confirmed by 1D X-ray diffraction (XRD) and atomic force microscopy (AFM), and the layer thickness was observed to be controlled with intercalated PS length between GO layers.     

Molecular dynamics simulation of mechanical performance of graphene/graphene oxide paper based polymer composites

Highly ordered polymer composites of layered graphene/graphene oxide (GO) sheets, i.e. graphene/GO paper, are attractive candidates for novel structural and functional applications. Here, molecular dynamics simulations are employed to elucidate the structural and mechanical properties of the graphene/GO paper based polymer composites. We find that the large scale properties of these composites are controlled by the conformation and content of polymer molecules within the interlayer galleries. Polymer conformations affect the interlayer spacing, while the polymer content controls the layer–matrix interactions, thereby affecting the elastic modulus of the composites. Additionally, the chemical composition of individual GO sheets also plays a critical role in establishing the mechanical properties of the composites. Specifically, a higher density of oxygen-containing groups leads to the decrease of elastic modulus of individual GO sheets. However, the groups also lead to the increased hydrogen bonds between the GO sheets and polymer molecules, resulting in the corresponding increase in overall stiffness. Our studies suggest the possibility of tuning the properties of graphene/GO paper composites by altering the conformation and content of polymer, as well as the density of functional groups on individual GO sheets.     

Effect of surface modification of graphene oxide on photochemical stability of poly(vinyl alcohol)/graphene oxide composites

Poly(vinyl alcohol) (PVA)/graphene oxide (GO) composites were prepared to improve the photochemical stability of PVA. The surface of GO was modified by oxyfluorination to introduce the polar functional groups on GO for the stronger interfacial interaction with PVA. The photochemical stability of PVA/oxyfluorinated-GO composites was evaluated by measuring the insoluble gel content after partial photodegradation of PVA under various UV irradiations. PVA/oxyfluorinated-GO composites showed the significant improvement in both the dispersion of GO in PVA matrix and the photochemical stability of PVA as the oxygen content increased in the oxyfluorination. The photochemical stability of composites had a close relation with the uniform distribution of GO in PVA matrix. The proper modification of GO by oxyfluorination showed the better photochemical stability for PVA/GO composites as compared to that of PVA/pristine GO composite.     

Reinforced polystyrene via solvent‐exfoliated graphene

Solvent‐exfoliated graphene (SEG)‐reinforced polystyrene (PS) composites were prepared using a straightforward solution‐casting method. SEG sheets, obtained by sonication‐assisted solvent direct exfoliation from natural graphite, were well dispersed in the PS matrix as evidenced from scanning electron microscopy and transmission electron microscopy observations. Addition of 0.5 wt% SEG resulted in a 6% increase in tensile strength and a 77% improvement in Young's modulus over pure PS due to the effective load transfer between SEG and PS matrix. The Young's moduli of the PS/SEG composites were obtained from both tensile experiments and calculations using the well‐established Halpin–Tsai model. Results from dynamic mechanical analysis indicated that the storage modulus of the PS/SEG composites was significantly improved relative to neat PS. The glass transition temperatures of the composites were found to increase substantially upon addition of SEG, consistent with differential scanning calorimetry analysis. © 2017 Society of Chemical Industry     

Preparation and properties of octadecylamine modified graphene oxide/styrene‐butadiene rubber composites through an improved melt compounding method

Octadecylamine modified graphene oxide/styrene‐butadiene rubber (GO‐ODA/SBR) composites are prepared by a novel and environmental‐friendly method called “Improved melt compounding”. A GO‐ODA/ethanol paste mixture is prepared firstly, and then blended with SBR by melt compounding. GO‐ODA sheets are uniformly dispersed in SBR as confirmed by scanning electron microscope, transmission electron microscopy, and X‐ray diffraction. The interfacial interaction between GO‐ODA and SBR is weaker than that between GO and SBR, which is proved by equilibrium swelling test and dynamic mechanical analysis. GO‐ODA/SBR show more pronounced “Payne effect” than GO/SBR composites, indicating enhanced filler networks resulted from the modification of GO with ODA. GO‐ODA/SBR composite has higher tensile strength and elongation at break than SBR and GO/SBR composite. The tensile strength and elongation at break for the composite with 5 parts GO‐ODA per hundred parts of rubber increase by 208% and 172% versus neat SBR, respectively. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 42907.     

Electrical,thermal, and mechanical properties of silicone foam composites filled with carbon-based nanofillers

It is critical to develop a new method to prepare engineered carbon-based fillers for high-performance applications. In this article, the functional nanocarbon-based fillers (FG-M) composed of multiwalled carbon nanotubes (MWNTs) and graphene oxide (GO) was synthesized by a simple self-assembly reaction under the existence of triethoxyvinylsilane. Based on the FG-M fillers, the silicone foam composites (FG-M/SF) were prepared, and the electrical, thermal, and mechanical properties of the composites were studied. Results showed that the FG-M could effectively improve the electrical, thermal, and mechanical properties of the composites compared with the single-filler system (GO/SF and MWNTs/SF). Especially, the composites exhibited the best synergistic effect on electrically, thermal and mechanical enhancement while the ratio of MWNTs and GO was close to 1:1. Moreover, the effect of type and content of fillers on the rheological properties and density of the composites was also studied. The result showed that the FG-M/SF system has good thixotropic and foaming performance. The FG-M filler will have a good application prospect in the preparation of high-performance SF composites.