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.     

Thermal-oxidative aging behavior of graphene and graphene oxide-filled nitrile butadiene rubber: A molecular simulation approach

Nitrile rubber (NBR) is commonly used as a stator rubber for screw pumps because of its excellent mechanical properties. However, under high-temperature conditions, using NBR for long-term operations is difficult, since it is highly susceptible to a thermal-oxidative aging phenomenon that leads to its failure. In this study, the thermal-oxidative aging behavior of graphene and graphene oxide (GO) in an NBR composite system was investigated using simulated molecular dynamics at 298 K and 348 K. The results showed that Young's moduli of graphene/NBR and GO/NBR composite systems were enhanced by about 33% and 44%, respectively, when the temperature was increased. That is, adding graphene and GO improved the resistance of NBR composites to elastic, bulk, and shear deformation, playing an important role in slowing down the thermal and oxygen aging of rubber. Furthermore, the binding energy, mean square displacement, and free volume fraction of the NBR composite systems were analyzed. The abundant oxygen-containing functional groups in GO increased the intermolecular interaction force between GO and NBR and effectively inhibited the migration of antioxidants 4020. Therefore, GO retards the thermal and oxygen aging of NBR composite systems more effectively.     

Synthesis and characterization of well-defined poly(l-lactide) functionalized graphene oxide sheets with high grafting ratio prepared through click chemistry and supramolecular interactions

Two simple and effective methods, “click” chemistry and supramolecular interactions, are demonstrated here to synthesize well-defined poly(l-lactide) (PLLA) functionalized graphene oxide (GO) sheets. We provide a simple method to introduce azide groups on GO sheets by the ring opening reaction of sodium azide with the epoxide groups of GO. The GO-N₃ sheets can easily undergo “click” reaction with alkyne-terminated PLLA by “grafting onto” method to produce GO/PLLA composites with high grafting ratio and exfoliated structure. Interestingly, GO-N₃ can be grafted with oxygen-containing polymers such as PLLA, polymethyl methacrylate (PMMA) or polyethylene oxide (PEO) via supramolecular interactions between the azide groups and these oxygen atoms on polymers, producing GO/polymer composites with low grafting ratio and intercalated structure. These “grafting onto” methods are useful to produce a variety of GO/polymer composites with different structure via “click” reaction or supramolecular interactions, which have potential applications in material science.     

Enhanced properties of polyvinyl chloride modified by graphene reinforced thermoplastic polyurethane

Graphene sheets with a range of unusual properties and thermoplastic polyurethane (TPU ) were combined to modify polyvinyl chloride (PVC ), and the enhanced properties such as flexibility, thermal stability and mechanical properties of the PVC were investigated. In order to avoid the C ? Cl bonds in PVC being weakened, graphene was incorporated into TPU in the melting state first and then this TPU was employed as a modifier to enhance and plasticize PVC in another melt blending step. In comparison with the ternary blending method, this step‐by‐step melt blending method was more efficient and convenient. The distribution of graphene sheets in the polymer matrix is uniform and no C ? Cl bond weakened effect can be observed. Due to the similar polarity, TPU showed good compatibility with PVC and its plasticizing effect allowed a broader range of low temperature flexibility of the modified PVC matrix. Moreover, other properties of the resultant PVC matrix (PTG ‐x ) including mechanical properties, thermal stability and plasticizer migration resistance were all found to be improved. With innovative applications in mind, the development of new graphene‐based materials will certainly lead to many future advances in science and technology. © 2017 Society of Chemical Industry     

Synthesis of glycidylethylhexylphthalate and its effects on poly(vinyl chloride) films as a novel plasticizer

To improve the processability and prevent the thermal degradation of poly(vinyl chloride) (PVC), various plasticizers and heat stabilizers have to be compounded. Phthalic plasticizers and metal soap stabilizers are usually used with epoxides as costabilizers. Epoxidized soybean oil (ESO), is one of the most commonly used epoxides because of its typical combined roles as a plasticizer and heat stabilizer in PVC compounds. ESO, however, sometimes causes surface contamination of PVC compounds because saturated fatty acids such as stearic and palmitic acids in soybean oil easily bleed onto the surface. In addition, some ingredients in ESO with hydroxide groups and unreacted double bonds during epoxidization also tend to increase the bleeding of ESO. This is due to their low compatibility with PVC resins. In this study, a novel plasticizer of PVC resins, glycidylethylhexylphthalate (GEHP), was synthesized, and its performance was evaluated. GEHP was designed to act as a plasticizer like normal phthalic plasticizers and to act as a heat stabilizer like ESO. Through the addition of epoxy groups in phthalic compounds, the resistance to bleeding was improved, and the plasticizing and heat‐stabilizing effects on the PVC compounds were preserved. Soft PVC films were prepared with GEHP. The mechanical properties, thermal stability, and bleeding properties of the films were investigated. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 96: 1347–1356, 2005     

Unusual functionalization of reduced graphene oxide for excellent chemical surface-enhanced Raman scattering by coupling with ZnO

A low-cost noble metal-free substrate comprised of annealed graphene oxide (GO)/ZnO composites is prepared to demonstrate an efficient chemical surface-enhanced Raman scattering effect. A high enhancement factor of about 10⁴, better than those reported for reduced GO (rGO)/Au and GO/Ag composites, is mainly attributed to the unusually abundant oxygen-containing groups generated on surface of rGO by coupling with ZnO nanoparticles at moderate temperature. High-resolution transmission electron microscopy, X-ray diffraction, and Fourier transform infrared spectroscopy are employed to examine the evolution of ZnO as well as reduction and functionalization of GO after different heat treatments.     

氧化石墨烯在水泥基体中的分散性及对其结构和性能的影响

为了解决氧化石墨烯(GO)纳米片层在水泥基体中的分散问题,制备了丙烯酸(AA)、丙烯酰氧乙基三甲基氯化铵(AAC)和丙烯磺酸钠(SAS)的共聚物(PAAS),PAAS与GO纳米片层形成PAAS/GO复合物并显示出分散作用。结果表明,w(PAAS)=2%分别与w(GO)=0.01%、0.02%和0.03%形成的复合物可使水泥基体分别形成由花状晶体、多面体状晶体和针状晶体构成的规整有序的微观结构,28 d时的抗折强度分别比对照样提高了63.0%、90.4%和87.9%,抗压强度分别提高了32.6%、74.2%和71.3%,同时这些水化晶体容易生长在裂缝、孔洞等缺陷处,具有修复结构缺陷的效果。PAAS通过与GO纳米片层形成复合物实现了GO在水泥基材料中的均匀分散以及对水泥基材料微观结构和性能的调控。     

Preparation and properties of dopamine reduced graphene oxide and its composites of epoxy

To improve the thermal and mechanical properties and further to expand its applications of epoxy in electronic packaging, reduced graphene oxide/epoxy composites have been successfully prepared, in which dopamine (DA) was used as reducing agent and modifier for graphene oxide (GO) to avoid the environmentally harmful reducing agents and address the problem of aggregation of graphene in composites. Further studies revealed that DA could effectively eliminate the labile oxygen functionality of GO and generate polydopamine functionalized graphene oxide (PDA‐GO) because DA would be oxidated and undergo the rearrangement and intermolecular cross‐linking reaction to produce polydopamine (PDA), which would improve the interfacial adhesion between GO and epoxy, and further be beneficial for the homogenous dispersion of GO in epoxy matrix. The effect of PDA‐GO on the thermal and mechanical properties of PDA‐GO/epoxy composites was also investigated, and the incorporation of PDA‐GO could increase the thermal conductivity, storage modulus, glass transition (T_g), and dielectric constant of epoxy. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 39754.     

Effect of base‐deposited graphene oxide on the thermal stabilization of poly(vinyl chloride)

Graphene oxide was deposited in a base solution to form base‐deposited graphene oxide (bd‐GO) particles. The structure and properties of the bd‐GO particles were evaluated using transmission electron microscopy, powder X‐ray diffraction and X‐ray photoelectron, Fourier transform infrared, UV‐visible and fluorescence spectroscopies. The effect of the bd‐GO particles on the thermal stabilization of poly(vinyl chloride) (PVC) was investigated using the Congo red test and thermogravimetric analysis. The results showed that the thermal stability of PVC was greatly improved by the bd‐GO particles. Furthermore, this stabilization mechanism was investigated using UV‐visible spectroscopy and nitrogen adsorption–desorption isotherm analysis. It was found that the improvement of thermal stability was mainly related to the deactivation of thermally labile structural defects in the PVC chains by the carboxylate and alkoxide moieties of the basic groups in the bd‐GO particles, and the highly efficient adsorption of the bd‐GO particles with hydrogen chloride produced during PVC degradation. © 2015 Society of Chemical Industry     

Effects of processing on the structure of PVC/montmorillonite composites. I. Melt and solution processes

The effects of processing conditions on the structure of poly(vinyl chloride) (PVC)/clay composites were investigated. Dry‐blending conditions were shown to affect composite structure in compression‐molded samples. PVC/(Cloisite Na) nanocomposites could not be prepared by melt compounding. Partially exfoliated and intercalated PVC/(Cloisite 30B) nanocomposites could be prepared by melt compounding. The effects of the grain structure of PVC resin and the PVC fusion mechanism on nanocomposite formation were considered. The particulate structure of the PVC resin was found to restrict the distribution ofclay, which could be improved by increasing the processing temperature. Almost fully exfoliated PVC/(Cloisite 30B) nanocomposites were prepared from solutions in tetrahydrofuran, and the plasticizer migration resistance of these composites was substantially improved. J. VINYL ADDIT. TECHNOL., 2011. © 2011 Society of Plastics Engineers     

Ionic liquid‐modified graphene/poly(vinyl alcohol) composite with enhanced properties

How to preserve the structure integrity of graphene while enhance its dispersion and compatibility in matrix attracts the attention of researchers in graphene/polymer nanocomposite field. In this paper, methacryloxyethyltrimethyl ammonium chloride (DMC), a kind of ionic liquids, was first used to non‐covalently functionalize graphene in the process of graphene oxide (GO) reduction. The as‐modified graphene (DMC‐rGO) was further incorporated into poly(vinyl alcohol) (PVA) matrix by solution casting technique to fabricate DMC‐rGO/PVA composites. The structure and properties of the obtained DMC‐rGO were investigated by X‐ray diffraction analysis (XRD), X‐ray Photoelectron Spectroscopy (XPS), Transmission Electron Microscope (TEM), Atomic force microscopy (AFM), and Raman test. The results showed that graphene could be successfully modified by DMC through ionic–π interaction and the structure integrity of the graphene could be reserved by this non‐covalently approach. Furthermore, after co‐reduction process, some hydroxyl groups were introduced into DMC‐rGO. In virtue of these intrinsic properties of DMC‐rGO, the fabricated DMC‐rGO/PVA composites exhibit considerable enhancements in mechanical properties and remarkable improvements in thermal stability, as well as the enhancement in electrical conductivity at low DMC‐rGO loading. This simple modification approach gives a new opportunity to improve the performances of graphene/polymer composites. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 45006.     

Preparation of graphene aerogel-poly(3,4-ethylenedioxythiophene) conductive composite by using simultaneous co-vaporized vapor phase polymerization

We prepared spherical reduced graphene oxide aerogels (rGOA) through freeze casting and thermal reduction for the fabrication of carbon-conducting polymer composites with excellent electrical and mechanical properties. The rGOA-poly(3,4-ethylenedioxythiophene) (PEDOT) or rGOA-PEDOT-SiO₂ composites were prepared by simultaneous co-vaporized vapor phase polymerization (SC-VPP). The rGOA spherical particles, prepared by freeze casting of GO solution, had a radially oriented pore structure at the center of its cross section and increasing density of GO sheet towards its center because the temperature gradient of the droplet of the GO solution rapidly freezes from the water outside the droplet during the process. The morphology of the rGOA-PEDOT-SiO₂ composites prepared using SCVPP was more spherical compared to rGOA-PEDOT composites, and the orientation of the cross-pore structure was well-developed. Moreover, micrometer-sized conductive PEDOT-SiO₂ hybrid spheres could be formed on the composite’s surface by controlling the amount of FTS oxidant. The rGOA-PEDOT-SiO₂ composites showed lower resistance values and higher current densities at the same voltage than rGOA or rGOA-PEDOT composites. This can be attributed to the surface area of the particle’s surface, which is enlarged due to the presence of the microspheres, which can cause the widening of the contact area with the electrode to facilitate better electron migration.     

A comparison of thermoplastic polyurethane incorporated with graphene oxide and thermally reduced graphene oxide: Reduction is not always necessary

Despite wide applications of reduced graphene-oxide (GO)-reinforced polymer-based composites, the necessity of the reduction procedure toward GO is still controversial. In this article, thermoplastic polyurethane (TPU) composites incorporated with GO and thermally reduced graphene oxide (TGO) were fabricated. GO and TGO exhibited different effects on crystallization behaviors, and mechanical and thermal properties of the TPU matrix. With 2.0 wt % filler loading, TPU composite reinforced by GO (TPU-GO-2 wt %) exhibited better thermal stability than that reinforced by TGO (TPU-TGO-2 wt %). The interfacial interaction between the nanofillers and the TPU matrix as well as their influence on the mobility of TPU chains were investigated, which proved that GO is superior to TGO in improving interface adhesion and maintaining crystallization of the TPU matrix. Compared with TPU-TGO-2 wt %, improved mechanical properties of TPU-GO-2 wt % were also evidenced owing to more oxygen-containing groups. This work demonstrates that the reduction of GO is not always necessary in fabricating polymer composites. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47745.     

Millimeter-long multilayer graphene nanoribbons prepared by wet chemical processing

Millimeter long multilayer graphene nanoribbons were prepared by a chemical treatment of graphite oxide (GO). To our knowledge, this is the very first report to harvest ultralong graphene ribbons with length dimension >1 mm using a wet chemical process. Scanning electron microscope (SEM) images reveal the nanoribbon length larger than 1 mm and width ∼10 μm. X-ray photoelectron spectroscopy (XPS) analysis shows that oxygen-containing functional groups decreased as the extent of the chemical treatment increased. X-ray diffraction (XRD) and Raman spectroscopy studies confirmed the XPS result and unveil more graphitic sheet like structure formed as GO was reduced by more concentrated NaOH. It is found that by adjusting NaOH/GO mass ratio during the chemical treatment, we can produce >1 mm long multilayer graphene nanoribbons and achieve controllable degree of reduction to the GO material. It is expected that this technique will make ultralong graphene nanoribbons readily available for research and applications.     

Pulsed laser assisted reduction of graphene oxide

We report a simple approach to reduce graphene oxide (GO) solution by pulsed laser irradiation. The reduction was rapidly carried out at room temperature in only 5 min. The reduced graphene oxide (r-GO) was characterized with UV–visible spectroscopy, X-ray diffraction, Raman spectroscopy, X-ray photoelectron spectroscopy, thermo-gravimetric analysis, Fourier transform infrared spectroscopy, scanning electron microscopy and atomic force microscopy. Based on this reducing method, an r-GO conductive film with a sheet resistance of 53.8 kΩ/sq was obtained. The pulsed laser reduction of GO in solution creates a new way to produce graphene composites for a variety of applications.     

改性氧化石墨烯/丁基橡胶复合材料的制备和隔声性能研究

通过Hummers法并以硅烷偶联剂KH-550为改性剂制备改性氧化石墨烯(GO),以改性GO作为补强填料、丁基橡胶(IIR)为橡胶基体制备改性GO/IIR复合材料,并对其性能进行研究。结果表明:加入改性GO制备的复合材料的拉伸强度先增大后减小,损耗因子峰值增大,阻尼温域扩宽,隔声性能略有提升;复合材料可以有效抑制单层镀锌钢板的共振和吻合效应,基于其阻尼特性制备的约束阻尼隔声板隔声性能明显提高。     

Perspectives of Epoxy/Graphene Oxide Composite: Significant Features and Technical Applications

In this article, advancement in epoxy/graphene oxide composites is presented. These materials are comprised of graphene oxide (GO) as filler (carbon-based material, thermodynamically stable, two-dimensional, planar and layered structure). Due to improved properties (mechanical response, low density, electrical resistance, and thermal stability), epoxy resins are used in several applications. Graphene oxide proposes unique properties to epoxy composites as high surface area, thermal and electrical conductivity as well as mechanical and barrier properties, relative to neat matrix. The corresponding significance of epoxy/GO-based materials, related challenges, and potential exploitation regarding technical applications (aerospace, gas sensor, electronic devices, etc.) have been overviewed.     

一种新型蓖麻油酸季戊四醇酯的制备及应用

用季戊四醇和蓖麻油酸通过酯化反应反应制备了蓖麻油季戊四醇酯。采用红外光谱仪和核磁共振仪对制备的产品的化学结构进行表征。并将其作为增塑剂与聚氯乙烯（PVC）共混,研究了塑化PVC的平衡扭矩、热性能和力学性能,对该增塑剂在不同溶媒中的耐迁移性进行了研究,并与邻苯二甲酸二辛酯和环氧大豆油的塑化性能进行了对比。结果表明,蓖麻油季戊四醇酯塑化PVC的加工平衡扭矩为14.9 N·m,改善了PVC的加工稳定性;塑化PVC的拉伸强度为23.28 MPa,断裂伸长率为263.13 %,耐迁移性能较邻苯二甲酸酯和环氧豆油较好,可以作为PVC增塑剂使用。     

氧化石墨烯复合水泥基材料的分子动力学模拟

氧化石墨烯（GO）边缘的大量含氧官能团具有更好的反应活性，能够有效的增强水泥基材料的性能。本文为探究氧化石墨烯中各含氧官能团对水泥基材料性能的影响，建立了GO/C-S-H、GO羧基/C-S-H、GO羟基/C-S-H和GO环氧基/C-S-H模型。采用分子动力学的方法对复合材料的力学参数、界面吸附能、动力学特性进行研究。结果表明：GO的加入使复合材料的杨氏模量提高了10.7%，泊松比提高了12%。GO中的环氧基有助于复合材料界面的稳定性，羟基有助于复合材料内部原子间作用更紧密。含氧官能团与钙原子间的钙氧键是粘聚力的来源之一，钙氧键键长的顺序为Ca-OH相似文献   

A simple two-step electrochemical synthesis of graphene sheets film on the ITO electrode as supercapacitors

In this study, a simple and controllable two-step electrochemical process is described for the synthesis of graphene sheets (GS) film on a cleaned indium tin oxide (ITO) sheet electrode. Namely, the main procedures involve the electrophoretic deposition (EPD) of graphene oxide (GO) film onto ITO electrode and the subsequent in situ electrochemical reduction (ECR) of GO to generate GS film. X-ray photoelectron spectroscopy (XPS) measurement demonstrates that most of the oxygen-containing functional groups in GO film have been removed after ECR. By electrochemical measurements, the maximum specific capacitance of the prepared GS film electrode was calculated to be 156 F g⁻¹, besides, the capacitance retention of the material remained 78% after 400 times of cycling, showing a promising prospect as supercapacitor materials.