Tunable Thermal Switch via Order–Order Transition in Liquid Crystalline Block Copolymer

Abstract

Organic material-based thermal switch is drawing much attention as one of the key thermal management devices in organic electronic devices. This study aims at tuning the switching temperature (<i>T</i>_S) of thermal conductivity by using liquid crystalline block copolymers (BCs) with different order-order transition temperature (<i>T</i>_tr) related to the types of mesogens in the side chain. The BC films with low <i>T</i>_tr of 363 K and high <i>T</i>_tr of 395 K exhibit reversible thermal conductivity switching behaviors at <i>T</i>_S of ∼360 K and ∼390 K, respectively. The BC films also exhibit thermal conductivity variation originating from the anisotropy of the internal structures: poly(ethylene oxide) domains and liquid crystals. These results demonstrate that the switching behavior is attributed to an order-order transition between BC films with vertically arranged cylinder domains and the ones with ordered sphere domains. This highlights that BCs become a promising thermal conductivity switching material with tailored <i>T</i>_S.