Improvement in thermal conductivity of amorphous polyimide (PI) by manipulation on the molecular scale

Abstract

Due to their excellent mechanical, chemical, and electrical properties, polymers are applied in numerous applications. However, polymers have a low thermal conductivity due to their entangled and disordered polymer chains and their weak interchain interactions. To enhance the thermal conductivity of polymers, numerous researchers have investigated the construction of thermally conductive polymer composites, the alignment of polymer chains, and the development of strong interchain interactions between polymer chains. In this study, in order to improve the thermal conductivity of polyimide, one of the polymers, nanofibers with aligned polymer chains was fabricated through electrospinning. Afterward, the π-π interaction, one of the strong interaction forces between polymer chains, was enhanced by high temperature and high pressure through hot-pressing. Therefore, high thermal conductivities of 0.44 and 0.98 Wm-1K-1 were observed for single PI nanofibers (INF-PI) manufactured by electrospinning and PI film (HP-PI) undergoing hot pressing, respectively. Compared to solution casting PI (SC-PI) in which the polymer chains are randomly oriented, these values are improved by a factor of 4.5 and 10.0, respectively. The spectroscopic analysis confirmed that this improvement in thermal conductivity was the result of a change in molecular scale. In addition to observing increases in thermal conductivity, mechanical and optical properties of polyimide are also studied.