Achieving synchronously high thermal conductivity and breakdown strength in PVA modulated via multiple ordered liquid crystal domains

Abstract

Polyvinyl alcohol (PVA) composites with concurrently high thermal conductivity (k) and breakdown strength (E_b) are highly desirable in various industry circle, however, high loading of inorganic fillers necessary for achieving a large k inevitably deteriorates the E_b, optical and mechanical performances of the composites. In this work, two kinds of liquid crystal (LC) organic molecules of 4,4′-bis(6-hydroxyloxy) biphenyl (BHHBP) and 4,4′-dihydroxydiphenyl (DOD), were employed to engineer ordered structure in PVA for simultaneously elevated k and E_b along with good mechanical and optical performances. This paper reveals how to achieve this goal via changing the mesogenic units into ordered domains in PVA via a self-assembly process. The findings indicate that the PVA dispersed with BHHBP and DOD showcase evidently higher k owing to the self-assembled ordered domains, paving highways for phonon transport leading to boosted k compared with neat PVA. Further, these multiple domains not only effectively impede long-distance charge migration, but also induce traps to capture charge carriers subsequently resulting in enhanced E_b. Therefore, the high k and E_b coupled with good mechanical flexibility and transparency, are concurrently achieved in PVA via inducing ordered LC domains and regulating their spatial dispersion in host matrix, which cannot be accomplished in traditional PVA composites. The developed PVA films with BHHBP domains present the synchronously high k (0.53 W/(m·K)) and E_b (95.3 kV/mm), low dielectric permittivity (3.0, 10³ Hz) and loss (0.035), along with good mechanical and optical performances, demonstrating promising potential utilizations in high frequency electronics and high-voltage power systems.