Solution-shearing of dielectric polymer with high thermal conductivity and electric insulation

Abstract

Polymer dielectrics, an insulating material ubiquitous in electrical power systems, must be ultralight, mechanically and dielectrically strong, and very thermally conductive. However, electric and thermal transport parameters are intercorrelated in a way that works against the occurrence of thermally conductive polymer electric insulators. Here, we describe how solution gel-shearing-strained polyethylene yields an electric insulating material with an outstanding in-plane thermal conductivity of 10.74 W m −1 K −1 and an average dielectric constant of 4.1. The dielectric constant and loss of such sheared polymer electric insulators are nearly independent of the frequency and a wide temperature range. The gel-shearing aligns ultrahigh-molecular weight polymer crystalline chains for the formation of separated and aligned nanoscale fibrous arrays. Together with lattice strains and the presence of boron nitride nanosheets, the dielectric polymer shows high current density carrying and high operating temperature, which is attributed to greatly enhanced heat conduction.

Emerging Flexible Thermally Conductive Films: Mechanism, Fabrication, Application

“…Similarly, Ronca et al [ 22 ] fabricated PE films with the reduced number of entanglements by uniaxially and biaxially stretching in the solid-state without any solvent, and the increase of k showed two separate regimes which was attributed to the initial crystal orientation and subsequent chain extension. Recently, Ren et al [ 78 ] reported a very simple solution gel-shearing method to fabricate PE films with an in-plane k of 10.74 W (mK) −1 , which is ascribed to the alignment and close packing of ultrahigh-molecular weight crystalline chains, facilitating the formation of separated nanocapacitor with high k (Fig. 6 b).…”

“…6 b). In brief, a shearing rod drags the UHMWPE solution gel across a heated substrate while driving the gel solution between the rod and the substrate, and then the UHMWPE film is formed and peeled off from the glass substrate at room temperature [ 78 ]. The used solution gel-shearing process is more facile than widely used ultradrawing process.…”

“…Reproduced with permission from Ref. [ 78 ]. Copyright 2021, American Association for the Advancement of Science.…”

State-of-the-art, opportunities, and challenges in bottom-up synthesis of polymers with high thermal conductivity

“…9,[21][22][23][24][25][26][27][28][29][30][31][32][33][34][35] Thermally conductive polymers will open up new avenues toward advanced thermal management applications such as chip packaging, soft robotics, and organic light-emitting diodes. 9,14,21,24,25,28,29,[36][37][38][39][40][41][42][43][44][45][46][47][48][49] Conventional conjugated polymers (e.g., polythiophene), composed largely of conjugated carbon-carbon double bonds, possess characteristically low thermal conductivity on the order of ∼0.1 W m −1 K −1 ; notably, graphene is also composed of conjugated carbon-carbon double bonds. 6,8 Graphene is one of the best thermal conductors with thermal conductivity greater than ∼2000 W m −1 K −1 .…”

“…9,21–35 Thermally conductive polymers will open up new avenues toward advanced thermal management applications such as chip packaging, soft robotics, and organic light-emitting diodes. 9,14,21,24,25,28,29,36–49…”