Dielectric,thermal and mechanical properties of hybrid PMMA/RGO/Fe2O3 nanocomposites fabricated by in-situ polymerization

Currently, the organic-inorganic hybrid materials have gained tremendous importance due to their unique applications in different technological fields. In this connection, the chemical synthesis of poly(methyl methacrylate) (PMMA) and its binary and ternary nanocomposites by in-situ bulk polymerization with various percentages of reduced graphene oxide (RGO) and hematite nanoparticles (Fe₂O₃ NPs) is presented. Dielectric properties of binary and ternary nanocomposites are investigated in the frequency range of 25 Hz-1 MHz for each composition. Ternary nanocomposite of PMMA with RGO:Fe₂O₃ NPs (2:2 wt%) exhibits a substantial enhancement of the dielectric constant up to ≈308 and suppressed dielectric loss of 0.12 at 25 Hz. Appearance of three types of interfaces in ternary PMMA nanocomposites accounts for the superior dielectric properties due to the accumulation of greater number of charges at the interfaces as compared to the binary nanocomposites with only one interface. The same optimized ternary PMMA nanocomposite shows a remarkable improvement in the thermal conductivity (2.04 W/mK), which is attributed to the formation of efficient thermal conducting pathways contributed by the synergic reduction in thermal resistance of both RGO and Fe₂O₃ NPs (2:2 wt%) relative to the binary nanocomposites PMMA/2 wt% RGO (1.04 W/mK) and PMMA/2 wt% Fe₂O₃ (0.98 W/mK). Thus, ternary nanocomposites prove to be the excellent candidates for thermal management applications. Furthermore, a comparison of the mechanical strength and thermal stability for all the binary and ternary nanocomposites is presented. In the last section, respective precursors and optimized binary and ternary nanocomposites are characterized by XRD, FTIR and SEM which reveal the strong interaction of respective nanofillers into PMMA matrix.     

Fabrication,Characterization and Dielectric Studies of NBR/Hydroxyapatite Nanocomposites

Nitrile rubber (NBR) based nanocomposite consists of different concentrations of hydroxyapatite nanoparticles (HA) were prepared and characterized by FTIR, UV and X-ray diffraction studies. The surface morphology of the nanocomposites were analyzed using SEM and optical microscopy. The glass transition temperature and thermal stability of NBR and its nanocomposites were done by DSC and TGA respectively. The electrical properties such as AC conductivity, dielectric constant and dielectric loss tangent were investigated in the frequency range of 10²–10⁶ Hz at room temperature. The FTIR spectra confirmed the interfacial interaction between NBR and the HA nanoparticles. The shift in the UV peak with broadness of composite indicates the formation of nanoparticles within the macromolecular chain of NBR. XRD pattern ascertained the ordered arrangement of nanoparticles with a decrease in the amorphous nature of parent polymer. Both the glass transition temperature and the thermal stability of the nanocomposites were higher than pure NBR and the glass transition temperature improved with the increase in concentration of nanoparticles in NBR composite indicating the strong interfacial adhesion between the polymer and nanoparticles. From DSC studies, thermodynamic parameters such as enthalpy and entropy change of the composites were also evaluated. AC conductivity of the nanocomposite was much greater than NBR and the magnitude of conductivity enhanced with the addition of nanoparticles. The observed enhancement in dielectric constant and dielectric loss tangent of composite with the increase in concentration of nanoparticle was attributed to the increase in number of interfacial interaction between the polymer and the nanoparticles.     

Preparation and properties of transparent zinc oxide/silicone nanocomposites for the packaging of high‐power light‐emitting diodes

New transparent zinc oxide (ZnO)/silicone nanocomposites with outstanding integrated properties, including a high UV‐shielding efficiency and transparency, bigger thermal conductivity, and lower dielectric constant, were successfully developed; they were prepared by the uniform dispersion of organic modified nano‐ZnO in a silicone matrix through in situ polymerization. The ZnO precursor was prepared by a direct precipitation method, which was then calcinated at different temperatures to produce nano‐ZnO with various morphologies and sizes. The effects of the size, surface nature, and content of nano‐ZnO on the key properties (e.g., optical and dielectric properties, thermal conductivities) of the composites were systematically investigated. The results show that the organic nano‐ZnO prepared by 3‐methacryloxypropyltrimethoxysilane can increase the dispersion of nano‐ZnO in silicone resin, and the interfacial adhesion between inorganic and organic phases, and consequently improve the integrated properties of nanocomposites. The increase of the particle content and size of ZnO in composites can lead to high thermal conductivity and UV‐shielding efficiency but lower visible‐light transparency, so there is an optimum content and size of ZnO in composites to obtain the best integrated properties of the composites. Specifically, the nanocomposite containing 0.03 wt % organic nano‐ZnO with an average size of 46 ± 0.4 nm not only had a high visible‐light transparency, UV‐shielding efficiency, and thermal conductivity but also possessed a low dielectric constant and loss and met the requirements of high‐performance electronic packaging for high‐power light‐emitting diodes. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Synthesis and properties of poly(methyl methacrylate)/montmorillonite (PMMA/MMT) nanocomposites

PMMA/MMT nanocomposites were successfully synthesized via in situ intercalative polymerization, and characterized by means of wide‐angle X‐ray diffractometry, transmission electron microscopy, thermal gravimetric analysis, dynamic mechanical analysis and Fourier‐transform infrared analysis. The nanocomposites possess partially exfoliated and partially intercalated structure, in which the silicate layers are exfoliated into nanometre secondary particles with thickness of less than 20 nm and uniformly dispersed in the polymer matrix. In comparison with pure PMMA, the thermal stability, glass transition temperature, and mechanical properties of the polymer are notably improved by the presence of the nanometric silicate layers. It was found that part of the PMMA chains in the nanocomposites are well immobilized inside and/or onto the layered silicates and, therefore, the unique properties of the nanocomposites result from the strong interactions between the nanometric silicate layers and the polymer chains. Copyright © 2003 Society of Chemical Industry     

Development of polyaniline/zinc oxide nanocomposite impregnated fabric as an electrostatic charge dissipative material

The paper presents the electrostatic charge dissipative performance of conducting polymer nanocomposite impregnated fabric based on polyaniline (PANI) and zinc oxide nanoparticles (ZnO NPs). Conducting polymer nanocomposites (PANI‐ZnO NPs) were synthesized by in situ chemical oxidative polymerization of aniline by using sodium dodecyl sulfate as surfactant and HCl as dopant. Coating of PANI‐ZnO nanocomposites on the cotton fabric was carried out during polymerization. The interaction of ZnO NPs with the PANI matrix was determined by Fourier transform infrared spectra (FTIR), TGA, XRD, scanning electron Microscopy (SEM), high resolution transmission electron microscopy (HRTEM) and conductivity measurements. The conductivity of PANI‐ZnO NP coated fabric was found to be in the range 10^?3 ? 10^?6 S cm^?1 depending on the loading concentration of ZnO NPs in the polymer matrix. TEM and HRTEM images showed that the PANI‐ZnO nanocomposites had an average diameter of 25–30 nm and were nicely dispersed in the polymer matrix. Antistatic performance of the nanocomposite impregnated fabric was investigated by static decay meter and John Chubb instrument. The static decay time of the film was in the range 0.5 ? 3.4 s on recording the decay time from 5000 V to 500 V. This indicated that the nanocomposite based on PANI‐ZnO nanocomposites has great potential to be used as an effective antistatic material. © 2015 Society of Chemical Industry     

Thermal,mechanical, and dielectric properties of polystyrene/expanded graphite nanocomposites

We herewith report the thermal, mechanical (modulus), and dielectric properties of polystyrene (PS)/expanded graphite (EG) nanocomposites fabricated by a simple technique of dispersing EG (up to 2.5 vol %) in PS matrix via solution method followed by hot pressing. The thermal stability and char yield of the nanocomposites are improved marginally. The modulus, electrical conductivity, dielectric constant, and dielectric loss tangent of the nanocomposites are significantly increased with EG content. The modulus of the nanocomposites increases by about twofold at 30°C compared with that of pure PS. The dielectric constant and the loss tangent of nanocomposites are increased up to 13‐fold and 200‐fold compared with that of pure PS, respectively, at 1 MHz and varied with frequency. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Enhanced dielectric constant and suppressed electrical conductivity in polymer nanocomposite films via loading MXene/TiO2/MoS2 nanosheets

Conductor/polymer nanocomposites can achieve high dielectric constant with low filler loading, but conductive fillers come into contact with each other easily, resulting in the formation of conductive paths. In this work, MXene/TiO₂/MoS₂ nanosheets were prepared by one-step hydrothermal method, and MXene/TiO₂/MoS₂/poly(vinylidene fluoride-co-hexafluoropropylene) (P(VDF-HFP)) nanocomposite films were prepared by solution casting method. At 1 kHz, with an optimized MXene/TiO₂/MoS₂ nanosheets loading of 8.0 wt%, MXene/TiO₂/MoS₂/P(VDF-HFP) nanocomposite films achieve a high dielectric constant of 944 and maintain a low dielectric loss of 0.19. TiO₂ and MoS₂ semiconductive layers on the surface of MXene nanosheets can prevent the formation of conductive paths, and therefore, nanocomposite films possess suppressed electrical conductivity. Moreover, MXene/TiO₂/MoS₂ nanosheets can build more microcapacitor structures in nanocomposite films with higher filler loading, which further improves the dielectric constant of nanocomposite films. Finite element simulation shows that TiO₂ and MoS₂ semiconductive layers can lower the electric field intensity and polarization intensity at the interface between conductive fillers and polymer matrix. Herein, MXene/TiO₂/MoS₂/P(VDF-HFP) nanocomposite films possess not only excellent dielectric properties, but also excellent mechanical properties, which can be used as flexible dielectric materials in electronic packaging technology.     

Electrical properties and thermal degradation of poly(vinyl chloride)/polyvinylidene fluoride/ZnO polymer nanocomposites

In this work, polymer nanocomposites consisting of a poly(vinyl chloride) (PVC) and polyvinylidene fluoride (PVDF) polymer network with ZnO nanoparticles as a dopant were prepared by solution casting. An XRD study of the PVC/PVDF/ZnO polymer nanocomposites shows predominantly sharp and high intensity peaks. However, the intensity and sharpness of the XRD peaks decreases with further increment in loading of ZnO (wt%), which reveals a proper intercalation of ZnO nanoparticles within the PVC/PVDF polymer system. Fourier transform infrared spectroscopy has been used to verify the chemical compositional change as a function of ZnO nanoparticle loading. TGA analysis clearly describes the thermal degradation of the pure polymer and polymer nanocomposites. The complex dielectric function, AC electrical conductivity and impedance spectra of these nanocomposites were investigated over the frequency range from 10 Hz to 35 MHz. These spectra were studied with respect to the Wagner ? Maxwell ? Sillars phenomenon in the low frequency region. Nyquist plots of the PVC/PVDF/ZnO nanocomposites were established from impedance measurements. The temperature‐dependent DC ionic conductivity obtained from the Nyquist plots follows Arrhenius behaviour. © 2016 Society of Chemical Industry     

保温时间对聚对亚苯基/LiNi-铁氧体纳米复合材料输运性能的影响

以溶剂热法合成聚对亚苯基/LiNi_0.5Fe₂O₄纳米复合材料,分别对放电等离子烧结时不同保温时间制备的样品的电导率和热导率进行了研究。发现,保温时间不同对聚对亚苯基/ LiNi_0.5Fe₂O₄纳米复合材料的电导率没有明显的影响,但对热导率具有一定的影响,保温时间越长热导率越大。保温时间延长,导致铁氧体晶粒长大,使材料体系的声子平均自由程增加,因此声子热导率增加,从而导致总热导率的增加。由于铁氧体具有较差的电输运特性,因此晶粒长大对电导率大小没有明显的影响。     

Ag-doped ZnO Reinforced Polymeric Ag:ZnO/PMMA Nanocomposites as Electron Transporting Layer for OLED Application

Nanostructured Ag-doped ZnO nanoparticles, and its polymeric nanocomposites (Ag:ZnO/PMMA) were synthesized in the laboratory via free radical polymerization process. The formation of PMMA matrix, its nanocomposites and relative changes in nano structured properties were examined by Fourier transform infrared spectroscopic (FTIR) analysis. Nanohexagonal structure was formed in the PMMA polymeric pattern with the incorporation of Ag:ZnO nano fillers, as examined by surface morphology images. Optical absorption spectra associated with the blue region of visible range and the optimized concentration showed reduced band gap ~2.55 eV which led to increase the p-type conductivity. Increased rate of electron–hole radiative recombination and an enhanced current density ~85.70% were examined. This revealed a significantly improved conductivity of the Ag:ZnO/PMMA nanocomposites. The nano fillers Ag:ZnO have fairly improved the optical absorption, conduction and an enhanced current density of nanocomposites which can be used as electron transport layer in the OLED device fabrication.     

Polylactide/graphite nanosheets/MWCNTs nanocomposites with enhanced mechanical, thermal and electrical properties

In this study, we have prepared a series of novel biodegradable polymer [polylactide (PLA)]-based nanocomposites using graphite nanosheets (GNs) and multi-walled carbon nanotubes (MWCNTs) by solution-blending technique and investigated their morphologies, structures, thermal stabilities, mechanical and dielectric properties, and electrical and thermal conductivities. Before preparation of the PLA/GNs/MWCNTs nanocomposites, the raw GNs used were endured a rapid expansion by thermal treatment. Temperature of this treatment had some obvious impacts on morphological changes of graphite nanosheets which were verified by means of scanning electron microscope (SEM) and X-ray diffraction (XRD) techniques. Resultant nanocomposites were characterized and evaluated by means of SEM, XRD, thermal conductivity measurements, tensile and impact tests, thermogravimetric analysis and dielectric measurements. Results obtained in this study indicated that thermal-expanded GNs in the presence of MWCNTs facilitate the formation of an appropriate conductive network in PLA matrix which resulted in a relatively low percolation threshold for thermal and electrical conductions of PLA/GNs/MWCNTs nanocomposites. Significant improvements in thermal and electrical conductivities, thermal stability and mechanical properties of PLA/GNs/MWCNTs nanocomposites obtained through the presence of both nanoparticles in PLA matrix were associated with their good co-dispersion and co-reinforcement effects. The macroscopic properties of nanocomposites were found to be strongly dependent on their components, concentrations, dispersion, and the resulted morphological structures.     

Eco-friendly poly(vinyl alcohol)/delaminated V2C MXene high-k nanocomposites with low dielectric loss enabled by moderate polarization and charge density at the interface

High-dielectric-constant (high-k) polymer/conductor composites with low dielectric loss are desirable for energy storage. However, high leakage currents from interfacial regions with high charge density are difficult to handle. In this work, high permittivity and low dielectric loss were achieved in poly(vinyl alcohol) (PVA)/V₂C MXene nanocomposite films fabricated by solution casting by taking advantage of the interfacial compatibility and moderate interfacial charge density of the nanocomposites. Water-soluble PVA was utilized as the polymer matrix. Delaminated V₂C MXene nanosheets with appropriate conductivity were prepared and used as the filler. The mild interface polarization of the nanocomposites was responsible for achieving favourable permittivity values. The small gap between the work functions of PVA and V₂C contributed to moderate interfacial charge density values and thus low dielectric loss values. A proportional correlation between the interfacial charge density and the conductivity of composites was also verified. The depth of charge injection from the MXene to PVA was found to be half of the interlamellar spacing of the delaminated MXene. The dependence of the electrical properties of the nanocomposites on the frequency and MXene content was also studied. The composite with 4 wt% MXene exhibited a permittivity of ~24 (16 times that of PVA) and a dielectric loss of ~0.14 (1.5 times that of PVA) at 1 kHz, as well as breakdown strength of ~31 MV m⁻¹ (63% of PVA). This work might enable environmentally friendly fabrication of promising composite dielectrics.     

Thermophysical properties of foliated graphite/nickel reinforced polyvinyl chloride nanocomposites

A novel, polymer‐based foliated graphite/nickel nanocomposites with high thermal conductivity, mechanical properties, and low dielectric constant was developed. The network structure of polyvinyl chloride (PVC) reinforced foliate graphite and nickel nanoparticles (GN) were tested in terms of X‐ray diffraction (XRD), scanning electron microscope (SEM), energy dispersive x‐ray analysis (EDX), and thermal‐gravimetric analyses (TGA). Thermogravimetric analysis revealed a large improvement in the thermal stability of PVC/GN nanocomposites. Thermal conductivity and diffusivity of the composites increased with increasing GN content and temperature. The obtained experimental thermal conductivity result are compared with the existing theoretical models. The measured values of thermal conductivity were in excellent agreement with those calculated from the Agari model. In addition, specific heat, coefficient of thermal expansion (TEC), micro porosity, and crosslinking density (CLD) of composites were investigated. The mechanical properties such as tensile strength, tensile modulus, hardness, and elongation at break of the nanocomposites were improved with inclusion GN which is proportional to GN content. Finally, the dielectric properties of PVC/GN nanocomposites as a function of frequency have been investigated in details. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Electrical properties of low density polyethylene/ZnO nanocomposites: The effect of thermal treatments

Low density polyethylene (LDPE)/ZnO nanocomposites were prepared by melt compounding followed by annealing or quenching treatment. Electrical properties of the thermally treated nanocomposites were investigated. The results showed that thermal treatments exerted a pronounced effect on the electrical properties of LDPE/ZnO nanocomposites. The dielectric constant of annealed LDPE/ZnO nanocomposites at various ZnO contents was higher than that of quenched nanocomposites. In sharp contrast, the resistivity of annealed LDPE/ZnO nanocomposites was considerably lower than that of quenched samples. The frequency dependence of dielectric constant was much pronounced for both the annealed and quenched LDPE/ZnO nanocomposites associated with the formation of ZnO network as the ZnO volume content reached 52 vol %. The structure–property relationship of the nanocomposites is discussed. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 1436–1444, 2006     

High dielectric constant epoxy nanocomposites containing ZnO quantum dots decorated carbon nanotube

Zinc oxide (ZnO) quantum dot (QD) decorated multi-walled carbon nanotube (MWCNT) hybrid was utilized in the fabrication of high dielectric constant epoxy nanocomposites. Because of the shielding effect of ZnO QD, the well-dispersed epoxy hybrid nanocomposites exhibit frequency insensitive high dielectric constant as well as greatly reduced dielectric loss. With only 1.5 wt% of MWCNT addition, the epoxy/MWCNT-ZnO nanocomposite possesses dielectric constant as high as 31 and dielectric loss as low as 0.01 at 1 kHz. In addition, the epoxy nanocomposite exhibits greatly enhanced tensile properties. The role of ZnO QD decorated MWCNT in the preparation and property improvement of multi-functional polymer nanocomposites is discussed.     

PMMA/o‐MMT nanocomposites obtained using thermally stable surfactants

In the preparation of polymer/montmorillonite (MMT) nanocomposites, the commonly used compatibilizers (cations of long carbon‐chain alkyl ammonium salts) present the drawback of a poor thermal stability. During bulk processing of nanocomposites elevated temperatures are usually required and, if processing temperature is close to decomposition temperature of the surfactant, decomposition will occur altering the interface between filler and polymer. To solve this problem, organically modified MMTs with thermally stable imidazolium surfactants have been prepared. A series of nanocomposites were obtained by dispersing o‐MMT in poly(methyl methacryate) (PMMA) matrix via an in situ free radical polymerization. The nanocomposites were characterized by X‐ray diffraction, transmission electron microscopy, gel permeation chromatography, thermogravimetric analysis, dynamic mechanical analysis, and nanoindentation measurements. The results showed that nanocomposite thermal stability depended on both the kind of used surfactant and degree of exfoliation. Under the same values of molecular weight, the nanocomposites containing imidazolium cations showed a better thermal stability with respect to the nanocomposite obtained using a standard alkylammonium surfactant. Dynamic mechanical and Nanoindentation measurements showed an improvement of mechanical properties, such as modulus and hardness, with respect to pure PMMA. Solution blending treatments on these nanocomposites led to obtaining of further improvement of the thermal performance. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41393.     

Morphological,structural, dielectric and electrical properties of PEO–ZnO nanodielectric films

The morphological, structural, dielectric and electrical properties of aqueous solution-cast prepared poly(ethylene oxide)–zinc oxide (PEO–ZnO) nanocomposite films have been investigated as a function of ZnO nanoparticle concentrations up to 5 wt%. Scanning electron microscopy (SEM) images of these films show that the morphology of pristine PEO aggregated spherulites changes into fluffy, voluminous and highly porous with dispersion of ZnO nanoparticles into the PEO matrix. X-ray diffraction (XRD) study confirms that the crystalline phase of PEO greatly reduces at 1 wt% ZnO, and it again increases gradually with further increase of ZnO concentration. The dielectric relaxation spectroscopy (DRS) over the frequency range 20 Hz–1 MHz reveals that the real part of complex dielectric permittivity at audio frequencies decreases non-linearly whereas it remains almost constant at radio frequencies for these polymeric nanocomposites. Dispersion of nanosize ZnO particles into the PEO matrix reduces the values of dielectric permittivity which also exhibits a correlation with the dispersivity of ZnO nanoparticles. The relaxation peaks observed in the dielectric loss tangent and electric modulus spectra reveal that the electrostatic interactions of nanoscale ZnO particles with the ethylene oxide functional dipolar group of PEO monomer units decrease the local chain segmental dynamics of the polymer. Real part of ac conductivity spectra of these films have been analyzed by power law fit over the audio and radio frequency regions, respectively, and the obtained dc conductivity values for these regions differ by more than two orders of magnitude. The temperature dependent relaxation time and dc conductivity values of the nanodielectric material obey the Arrhenius relation of activation energies and confirm a correlation between dc conductivity and PEO chain segmental motion which is exactly identical to the characteristics of solid polymer electrolytes. Results imply that these nanocomposite materials can serve as low permittivity flexible nanodielectric for radio frequency microelectronic devices and also as electrical insulator for audio frequency operating conventional devices in addition to their suitability in preparation of solid polymer electrolytes.     

Enhanced through-plane thermal conductive properties of Ag/rGO nanocomposite

High thermal conductivity of nanocomposite-based polymer matrix is one of the most important keys in developing many heat exchanger instruments. Here, we report a novel nanocomposite system based on silver-coated reduced graphene oxide (Ag/rGO) in silane cross-linked low-density polyethylene (XLPE) matrix with unprecedented through-plane thermal conductivity. Compared to the virgin rGO, Ag/rGO nanocomposite showed 67% higher thermal conductivity due to the Ag nanoparticles (NPs) decoration. The Ag NPs within the nanocomposites are believed to act as a thermal conductor among rGO nanosheets and eventually enhance the heat conduction in 3D manner.     

High‐performance flexible epoxy/ZnO nanocomposites with enhanced mechanical and thermal properties

Flexible epoxy/ZnO nanocomposites were prepared using different loadings of ZnO nanoparticles (NPs) and nanotubes (NTs) via in situ curing of epoxy with polyoxyethylene diamines (ED₆₀₀). ZnO precursor was synthesized via precipitation method and ZnO NPs with an average size of 25 nm were used in the preparation of the nanocomposites. ZnO NTs with an average outer diameter, length of 200 nm and 2.4 µm respectively, were prepared by the wet method (hydrothermal method). The morphology, structure, and composition of the nanocomposites were characterized by transmission electron microscopy (TEM), scanning electron microscopy (SEM), X‐ray diffraction (XRD), Fourier transform infrared spectroscopy (FT‐IR), and thermo‐gravimetric analysis (TGA). The effect of morphology and content of nano‐ZnO materials on the thermal and mechanical properties of flexible epoxy was studied. In addition, the hardness and indentation depth were calculated by means of nanoindentation. Results showed that the mechanical and thermal properties of flexible epoxy were enhanced by incorporation of ZnO nanostructure into the polymer matrix. POLYM. ENG. SCI., 57:932–946, 2017. © 2016 Society of Plastics Engineers     

Electrical properties of flexible graphene reinforced polyimide composites

The electrical properties of polyimide and the composite at different volumes fractions were studied in the frequency range 200–20 kHz and in the temperature range 30–200 °C. Increasing the volume fraction of graphene up to 10%, resulted in an extremely large increase in the dielectric constant, which indicates the composites remarkable ability to store electric potential energy under the effect of alternating electric field. An increase in dielectric constant was also observed with increasing temperature and decreasing frequency. The outstanding dielectric properties of polyimide graphene nanocomposites are attributed to the large volume fraction of interfaces in the bulk of the material. The measured increase in dielectric constant with increasing temperature was attributed to the segmental mobility of the polymer chains. The AC conductivity for polyimide and the composites was calculated from the loss factor and a remarkably high conductivity was obtained for the composites due to the formation of conducting paths in the matrix by the graphene sheets. Also this study showed that the thermal conductivity of the composites increased sharply with increasing graphene concentration. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 45372.