Enhancing thermal conductivity of amorphous polymers

Department of Mechanical EngineeringHigh thermal conductivity of polymers is important to improve the functionality and reliability of products by efficiently dissipating heat in polymer products. Several studies have demonstrated that extended polymer chain conformation enhances the heat transfer in amorphous polymers. Here, we demonstrate that the tacticity of polymers alters the chain conformation in ionized polymers due to the difference in the coulombic interaction among the functional groups. Depending on their tacticity, polymers with the similar degree of ionization were observed to have significantly different cross-plane thermal conductivities, as high as 1.14 W/m???K in ionized atactic poly(acrylic acid)(PAA) and 0.69 W/m???K in ionized syndiotactic poly(methacrylic acid)(PMAA) but merely 0.55 W/m???K in ionized isotactic PAA and 0.48 W/m???K in ionized isotactic PMAA and atactic PMAA. Elastic modulus, viscosity data which affects the conformation of the polymer chain, suggested validating effect on the thermal conductivity of polymers. In addition, we have systematically investigated the effect of annealing temperature on the cross-plane thermal conductivity of an amorphous natural bio-polymer. The results display a systematic increase in thermal conductivity (0.2 W/m???K to 1.3 W/m???K) with annealing temperature. This high thermal conductivity is mainly achieved by improving the crystallinity of polymer and low inter-planar spacing resulted to efficient phonon transport.clos

Low-cost synthesis of high quality graphene oxide with large electrical and thermal conductivities

A simple and cost-effective method for synthesizing high quality thermally reduced graphene oxide (TrGO) thin films using Shellac, is presented. The synthesis temperature ranges from 550 degrees C to 900 degrees C, and is the sole control parameter to obtain a carbon content as high as 97 atomic percentage. For TrGO synthesized at 900 degrees C, its XPS, Raman, and TEM data indicate a large portion of sp(2) hybridized carbon atoms and large crystal sizes (similar to 1 mu m), which resulted in very high electrical and cross-plane thermal conductivities, 2488 S/cm and 1.3 W/m-K, respectively. Furthermore, this high electrical conductivity of TrGO was observed to remain unaffected under mechanical stress 10 times higher than that completely broke solution-processed reduced graphene oxide (rGO) films, promising its potential for robust, transparent, and cost-effective conductive coating. (C) 2021 Elsevier B.V. All rights reserved

Tacticity-dependent cross-plane thermal conductivity in molecularly engineered amorphous polymers

The low thermal conductivity of polymers impedes heat dissipation in plastic products and often limits their functionality and reliability. Extended polymer chain conformation (i.e., planar zigzag) has widely been found to enhance heat transfer in both a single polymer chain and bulk polymers. Here, we show that the tacticity of polymers (poly(acrylic acid) (PAA) and poly(methacrylic acid) (PMAA)) significantly affects the thermal conductivity of ionized polymers, in which the extended chain conformation is induced by electrostatic repulsion. Depending on their tacticity, polymers with similar degrees of ionization were observed to have significantly different thermal conductivities, as high as 1.14 W m(-1)center dot K-1 in ionized atactic PAA and 0.69 W m(-1)center dot K-1 in ionized syndiotactic PMAA, but only 0.55 W m(-1)center dot K-1 in ionized isotactic PAA and 0.48 W m(-1)center dot K-1 in ionized isotactic PMAA. The elastic modulus, degree of ionized carboxyl groups, and viscosity data suggest that the size and spatial arrangement of side groups, which influence the conformation of the polymer chain, affect the thermal conductivity of polymers

Direct growth of thermally reduced graphene oxide on carbon fiber for enhanced mechanical strength

In this study, carbon fiber (CF) composites were prepared by synthesizing thermally reduced graphene oxide (TRGO) directly on the surface of CFs in order to reinforce the interface between the CFs and the matrix. The conformal and robust coating of TRGO on the CF surface is achieved by the direct conversion of shellac, a lowcost natural polymer, to TRGO via single-step low-temperature (400-700 degrees C) annealing. X-ray photoelectron spectroscopy, Raman analysis, Fourier-transform infrared spectroscopy, scanning electron microscopy, transmission electron microscopy, atomic force microscopy, contact angle measurement, and energy dispersive spectrometry results confirmed the synthesis of high-quality TRGO, which prompted hydrogen bonding and mechanical interlocking at the composite interfaces. The CF-TRGO composites showed 60 and 152% higher interlaminar shear strength (ILSS) and flexural strength, respectively than the untreated CF composites. The fracture surface analysis by SEM further reveals that the interfacial bonding between the matrix and the CFs increased significantly with TRGO coating