Highly conductive graphene by low-temperature thermal reduction and in situ preparation of conductive polymer nanocomposites

Polydopamine-coated graphene oxide (DGO) films exhibit electrical conductivities of 11?000 S m(-1) and 30?000 S m(-1) upon vacuum annealing at 130 °C and 180 °C, respectively. Conductive poly(vinyl alcohol)/graphene and epoxy/graphene nanocomposites show low percolation thresholds due to the excellent dispersibility of the DGO sheets and their effective in situ reduction.     

Mechanical,thermal conductive,and dielectric properties of fluoroelastomer/reduced graphene oxide composites in situ prepared by solvent thermal reduction

Fluoroelastomer (FKM)/reduced graphene oxide (rGO) composites are in situ prepared by solvent thermal reduction method in N,N‐dimethylformamide (DMF) solution. The reduction of graphene oxide (GO) is characterized by X‐Ray photoelectron (XPS), ultraviolet–visible (UV–vis), and Fourier transform infrared (FTIR) spectra. GO and rGO are both efficient fillers to improve the mechanical properties of FKM. The dispersibility of rGO is improved after solvent thermal reduction which is confirmed by scanning electron micrograph (SEM) and X‐ray diffraction (XRD). The homogenous suspension of FKM/rGO composites in DMF can stay stable for more than a month. The dielectric permittivity of FKM/rGO (5 phr) is 26.4 at the frequency of 10⁻¹ Hz, higher than the pure FKM (8.1). The thermal conductivity of rGO/FKM composites increases. POLYM. COMPOS., 35:1779–1785, 2014. © 2013 Society of Plastics Engineers     

In situ chemical reduction and functionalization of graphene oxide for electrically conductive phenol formaldehyde composites

We report an efficient one-step approach to reduce and functionalize graphene oxide (GO) during the in situ polymerization of phenol and formaldehyde. The hydrophilic and electrically insulating GO is converted to hydrophobic and electrically conductive graphene with phenol as the main reducing agent. Simultaneously, functionalization of GO is realized by the nucleophilic substitution reaction of the epoxide groups of GO with the hydroxyl groups of phenol in an alkali condition. Different from the insulating GO and phenol formaldehyde resin (PF) components, PF composites are electrically conductive due to the incidental reduction of GO during the in situ polymerization. The electrical conductivity of PF composite with 0.85 vol.% of GO is 0.20 S/m, nearly nine orders of magnitude higher than that of neat PF. Moreover, the efficient reduction and functionalization of GO endows the PF composites with high thermal stability and flexural properties. A striking increase in decomposition temperature is achieved with 2.3 vol.% of GO. The flexural strength and modulus of the PF composite with 1.7 vol.% GO are increased by 316.8% and 56.7%, respectively.     

Self-healable and reprocessible liquid crystalline elastomer and its highly thermal conductive composites by incorporating graphene via in-situ polymerization

The booming of modern electronic devices featuring increasing power and multi-functionalization demands novel high thermal conductive materials with various functions, such as self-healing property and high deformability, while traditional polymer-based or metallic-based materials could hardly provide. Therefore, we report a high thermal conductive and disulfide-based self-healable and reprocessible liquid crystalline elastomer (SHLCE) composite by incorporating graphene nanoplates (GNPs) fillers. The obtained GNPs/SHLCE composites exhibited desired thermal conductivity (5.08 Wm⁻¹ K⁻¹) when the content of GNPs was 20 wt% to the composites. Moreover, the GNPs/SHLCE composites showed intriguing recycled performance (Tensile strength after recycle could maintain over 93% compared with that of original composites). Furthermore, we concluded that the improved thermal conductivity of GNPs/SHLCE composites was beneficial to the thermal induced reprocessible and shelf-healable systems.     

Preparation of conductive polypyrrole composites by in‐situ polymerization

Two kinds of conductive polypyrrole composites were prepared by in‐situ polymerization of pyrrole in a suspension of chlorinated polyethylene powder or in a natural rubber latex using ferric chloride as oxidizing agent. The preparation conditions were studied and the results showed that it is better to swell the chlorinated polyethylene powder with the monomer first, followed by addition of the oxidant, than to add the oxidant first, and that conversion can reach 98% for 6 h at room temperature. The conductivity percolation threshold of the composite is about 12%. The composites can be processed repeatedly, exhibiting a maximum tensile strength over 9 MPa and a maximum conductivity near 1 S cm⁻¹. The polypyrrole/natural rubber composites were prepared successfully by using a nonionic surfactant (Peregal O) as stabilizer at pH less than 3 with a molar ratio of FeCl₃/pyrrole = 2.5 below 45 °C. The latter composites show a low conductivity percolation threshold about 6%, a maximum tensile strength over 10 MPa and a maximum conductivity over 2 S cm⁻¹. The composites were characterized by FTIR and TGA. The polypyrrole/chlorinated polyethylene composites are very stable in air and almost no decrease of conductivity was observed for over 10 months examined. © 1999 Society of Chemical Industry     

Multifunctional polyimide/graphene oxide composites via in situ polymerization

In this article, we detail an effective way to improve electrical, thermal, and gas barrier properties using a simple processing method for polymer composites. Graphene oxide (GO) prepared with graphite using a modified Hummers method was used as a nanofiller for r‐GO/PI composites by in situ polymerization. PI composites with different loadings of GO were prepared by the thermal imidization of polyamic acid (PAA)/GO. This method greatly improved the electrical properties of the r‐GO/PI composites compared with pure PI due to the electrical percolation networks of reduced graphene oxide within the films. The conductivity of r‐GO/PI composites (30:70 w/w) equaled 1.1 × 10¹ S m^?1, roughly 10¹⁴ times that of pure PI and the oxygen transmission rate (OTR, 30:70 w/w) was reduced by about 93%. The Young's modulus of the r‐GO/PI composite film containing 30 wt % GO increased to 4.2 GPa, which was an approximate improvement of 282% compared with pure PI film. The corresponding strength and the elongation at break decreased to 70.0 MPa and 2.2%, respectively. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40177.     

Highly thermal conductive graphene/carbon nanotubes films with controllable thickness as thermal management materials

As electronic devices continue to be integrated and miniaturized, the increased system power density leads to a continued increase in operating temperature, ultimately leading to degradation of stability and performance. Therefore, the development of thermal management materials with superior thermal conductivity is urgently needed. Herein, full-carbon graphitized graphene/carbon nanotubes (CNTs) (gGC) films with controlled thickness were fabricated through compositing followed by compaction. The appropriate amount of CNTs doping enlarges the crystallinity and improves the stacking order of the composite film during the structural evolution process. Ultimately, the thermal synergy between CNTs and graphene sheets accelerates the propagation of phonons and endows the free-standing gGC film with good performance. The flexible gGC film shows an in-plane thermal conductivity of 1280.3 W/mK, an electrical conductivity of 6559 S/cm, and the foldability of 10,000 times at a thickness of 30 μm. Moreover, gGC films with controllable thicknesses were successfully prepared through a convenient “multilayer compaction” strategy, which allows thick gGC films to maintain a high level of thermal dissipation, while effectively mitigating the rapid decline in thermal conductivity of the films with increasing thickness. This work provides a general method for the realization of large-scale and convenient production of high-thermally conductive thick films.     

Tuning graphene properties by a multi-step thermal reduction process

A multi-step thermal reduction process to produce graphene from graphite oxide was developed to optimize the degree of reduction, its BET surface area and its suitability as electrode in electrochemical energy storage devices. The procedure combines an initial flash pyrolysis to a temperature below 460 °C and a subsequent ramp-heating treatment up to the selected final temperature. With this methodology, the morphology of the graphene materials obtained, which has a great influence in their behavior as electrodes, is controlled.     

石墨烯导热高分子复合材料的制备、性能与机理

石墨烯是一种具有超大的比表面积、良好的热和化学稳定性、超高的热导率以及易于化学修饰的蜂窝状单层碳材料,已作为填料广泛应用于导热高分子复合材料领域。近年来石墨烯导热高分子材料的研究重点是改善石墨烯在聚合物基体中的界面相容性和分散性能。阐述了近年来石墨烯导热高分子复合材料的制备方法及其热性能,并重点对石墨烯导热高分子复合材料的导热机理进行综述,同时结合研究现状对石墨烯导热高分子复合材料的研究方向进行展望。     

In situ polymer/polymer composites from poly(ethylene terephthalate), polyamide-6, and polyamide-66 blends

In situ reinforced binary and ternary polymer/polymer composites are obtained by the melt blending of poly(ethylene terephthalate) (PET), polyamide-6 (PA-6), and polyamide-66 (PA-66) in an extruder in the presence of a catalyst, followed by drawing of the extrudate and annealing of the drawn blends. The blends were studied by DSC, X-ray, SEM, and mechanical testing. After drawing, all the components were found to be oriented, forming microfibrils with diameters of about 1–2 μm. The chemical nature of the homopolymers affects the blends' morphologies; while the PA-66/PA-6 blend is homogeneous, phase separation is established in the case of PET/PA-6. The decrease in the enthalpy of melting of the blend components as well as the depression of their peaks of crystallization from the melt, compared to pure homopolymers, are indications that block copolymers have been formed via interchange reactions during the blending process. On the one hand, these copolymers improve the compatibility of the homopolymers, and on the other hand, they alter the chemical composition of the blends. After thermal treatment at 245°C, i.e., above the T_m of PA-6, the latter undergoes some disorientation, while PET and PA-66 retain their microfibrillar shape, and in this way, a compositelike structure is created. The presence of chemical bonds between the separate phases via copolymers favors the cocrystallization of PA-66 and PA-6 as well as the cooperative crystallization of PET, PA-6, and PA-66, both modes fostering improved compatibility (adhesion) of the blend components. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 67: 723–737, 1998     

Simultaneous surface functionalization and reduction of graphene oxide with octadecylamine for electrically conductive polystyrene composites

Simultaneous surface functionalization and reduction of graphene oxide (GO) was realized by simple refluxing of GO with octadecylamine (ODA) without the use of any reducing agents. The presence of the long octadecyl chain made the hydrophilic GO hydrophobic, evidenced by the selective dispersion of the ODA-functionalized GO (GO–ODA) in chloroform solvent rather than in water. Interestingly, different from the insulating GO, GO–ODA became electrically conductive due to the reduction in the presence of ODA. The electrical conductivity of GO–ODA was further increased by incidental thermal reduction during the compression-molding of its polystyrene (PS) composites at 210 °C, which exhibited a sharp transition from electrically insulating to conducting with a low percolation threshold. The high conductivity of the PS/GO–ODA composites is attributed to the improved dispersion and the reduction of GO–ODA in comparison with GO.     

Electrically conductive textiles by in situ polymerization of aniline

Two methods of obtaining electrically conductive fabrics by in situ polymerization of aniline were compared. Conductive fabrics were prepared by immersing the nylon 6 fabrics in 100% aniline or an aqueous hydrochloride solution of aniline followed by initiating successive polymerization in a separate bath (DPSB) or in a mixed bath (DPMB) of oxidant and dopant solution with aniline. In each case, the polymerization conditions were optimized to obtain the maximum quality of polyaniline (PAn) on the fabrics. The higher conductivity of composite fabrics, whose value reached up to 0.6 × 10⁻¹ s/cm, was obtained by the DPMB process. Moreover, this method induced the least decrease in the degree of crystallinity as compared to the DPSB process. The serviceability of the PAn–nylon 6 composite fabrics was also evaluated. No significant changes in the conductivity were observed after abrading the composite fabrics over 50 cycles and multiple acid and alkali treatment. The stability of conductivity was slightly decreased by less than 1 order after exposure to light for 100 h, but it was significantly decreased after washing with detergent. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 2094–2101, 1999     

Copper nanowire/PA6 composites prepared by in situ polymerization and its properties

Most magnetic composite materials have a serious sedimentation problem because of their large density. When the nanomaterials are combined with magnetic materials, the density would become larger. In this article, polystyrene (PS) beads were used as core to synthesize raspberry-like PS-Fe₃O₄@TiO₂ particles (PFTPs) by a facile method, which could float on the water. The loaded Fe₃O₄@TiO₂ particles were characterized by X-ray diffraction (XRD), which could confirm the anatase phase TiO₂ coated on Fe₃O₄ nano-particles. Transmission electron microscopy (TEM) and scanning electron microscopy (SEM) confirmed the presence of acrylic acid in reaction media could effectively tune the morphology of resulting composite particles between “core-shell” and “raspberry-like”. The data of Vibrating sample magnetometer (VSM) indicated the change in saturation magnetization before and after TiO₂ coated, the introduction of PS could further influence the saturation magnetization of Fe₃O₄. Lastly, we proved the sedimentation stability of PFTPs via capturing the photographs of them in water and oil.     

Enhanced mechanical and thermal properties of polyurethane/functionalised graphene oxide composites by in situ polymerisation

ABSTRACT

Isocyanate-functionalised graphene (iGO) was prepared and incorporated into a thermoplastic polyurethane via an in situ polymerisation. Firstly, graphene oxide was successfully modified using a mixture of isocyanate- and diisocyanate-containing compounds, leading to the formation of good dispersions of resulting functional graphene oxide in organic solvents, such as N,N-dimethylacetamide and N,N-dimethylformamide. The addition of iGO into polyurethane matrix improved both mechanical and thermal properties in the polyurethane/iGO composites relative to neat polyurethane. An addition of only 0.03?wt-% of functionalised graphene into the polyurethane increased Young’s modulus by 1.4 times and tensile strength by two times. Meanwhile, the elongation at break was similar to that of the neat polymer. In addition, dynamic mechanical analysis also confirmed the improvement in storage modulus of the polymer composites especially at high-temperature range. We believe that the developed modification approach for graphene oxide and polyurethane/graphene composites presented herein could be useful in polymer/graphene composite development.     

导电型聚合物/石墨烯复合材料的研究进展

分别介绍了导电型聚合物/石墨烯复合材料的导电机理、制备方法以及相关的应用领域,分析了导电型聚合物/石墨烯复合材料目前存在的一些问题,并对导电型聚合物/石墨烯复合材料的未来发展作出了一定展望。     

原位聚合尼龙6/纳米SiO2复合材料的研究

将经湿法处理的纳米SiO_2处理液直接加入到己内酰胺反应物中,原位水解开环聚合制备了尼龙6/纳米SiO_2复合材料,表征了该纳米SiO_2复合材料的相对分子质量、结晶结构和热性能等。结果表明,尼龙6纳米SiO_2复合材料随着纳米SiO_2含量的增加,尼龙6的相对分子质量降低,结晶度与熔点略有下降,储能模昔幅度提高。     

Flammability and thermal behavior of phosphorus-containing polyamide-6

An investigation is reported on the flammability and thermal behavior of polyamide-6, obtained by anionic polymerization of ?-caprolactam, carried out in bulk, in the presence of the following N-substituted phosphorus-containing lactam derivatives: diethyl-(N-caprolactam)-phosphonite (PL₁), diethyl-(N-caprolactam)-phosphonate (PL₂), and 2,5-dichlorophenyl-bis(N-caprolactam)-phosphinate (PL₃). Phosphorus-containing lactam derivatives PL,₁ and PL₃ are used as activators of the anionic polymerization of ?-caprolactam, and PL₂, as a modifying additive. The phosphorus-containing polyamide-6 possesses improved flame retardancy, as well as improved thermo- and thermooxidative resistance. Destruction kinetics were studied in nitrogen and air atmospheres, and the activation energy for thermal and thermooxidative destruction have been determined. The effect of PL₁ PL₂, and PL₃ on the melting temperature (T_m) and glass-transition temperature (T_g) of polyamide-6 was established. © 1993 John Wiley & Sons, Inc.     

Preparation of polyacrylonitrile/graphene oxide by in situ polymerization

Highly oriented molecular structure is essential for high‐performance carbon fibers. The addition of a small amount of graphene sheets may enhance the degree of molecular orientation of precursor fibers during spinning and stabilization by limiting the disorientation of the chain segments. Graphene sheets merge into the carbon fiber structure during carbonization. The structure and properties of polyacrylonitrile containing graphene oxide (GO) prepared by in situ polymerization were investigated. With increasing GO loading, the molecular weight of the polymer decreased gradually from 69 000 g mol^?1 for the sample without GO to 60 600 g mol^?1 for the sample with 2.5 wt% loading of GO. Scanning electron microscopy and X‐ray diffraction results indicated that GO was dispersed in single layers in the polymer matrix. The degree of crystallization of the polymer with 0.5 wt% GO was increased by 8%. Moreover, differential scanning calorimetry and thermogravimetric analysis showed that an appropriate amount of GO, e.g. 0.5 wt%, made the carbon yield of the polymer increase by 5.0 wt%, because the GO in the composite improved the intermolecular crosslinking reaction. Copyright © 2012 Society of Chemical Industry     

GO表面原位生长CNTs改善聚丙烯导热复合材料分散与界面形态

二维结构氧化石墨烯(GO)纳米片在高分子导热复合材料领域有良好应用前景,但常受限于片层间相互作用过大导致的局部团聚,不利于力学性能和导热性能的提高。借助GO纳米片表面和边缘提供的大量活性位点以吸附铁基催化剂,进而通过微波辅助合成方法在GO表面原位生长碳纳米管(CNTs)的策略,在数分钟内合成具有三维多层次结构的纳米杂化体(GO-CNT)。通过常规熔融共混方法,可获得GO-CNT在聚丙烯(PP)基体中良好剥离与均匀分散形态,明显不同于GO/PP复合体系中严重的局部团聚现象。均匀分散的GO-CNT对PP复合材料的力学性能和导热性能提升效果显著：在3%(质量分数)含量下,复合材料的屈服强度和热导率分别达到了38.0 MPa和0.76 W/(m·K),较纯PP增幅分别为20%和230%,明显优于传统GO改性复合材料。本研究为解决纳米片状填料在导热复合材料中的应用瓶颈提供了可行的结构设计策略和复合材料制备方法。     

Simultaneous in situ reduction,self-alignment and covalent bonding in graphene oxide/epoxy composites

Graphene oxide (GO)/waterborne epoxy (EP) composites are prepared using an easy, all aqueous, in situ polymerization method. GO is reduced in situ using hydrazine to achieve highly stable reduced graphene oxide (rGO)/EP dispersions, leading to the formation of composites with a self-aligned layered structure and highly anisotropic properties between the direction of alignment and that perpendicular to it. The strong covalent bonding between the epoxy and rGO and the highly aligned, ultralarge rGO sheets give rise to a remarkable percolation threshold of 0.12 vol.%, as well as much improved mechanical, electrical and thermal properties of the composites in the alignment direction. They outperform those containing GO sheets that are bonded to the epoxy matrix through a weaker π–π stacking mechanism.