Thermal Diode Films with Liquid Crystal Elastomer Microstructures

Abstract

Thermal diodes enabling asymmetric heat flow via efficiently conducting heat in one direction while blocking it in the opposite direction have great potential for controlling and managing thermal energy. Here, a thermal diode film with a scalable and thin-film form factor is presented, which utilizes thermal contact asymmetry that varies with the direction of heat flow. The proposed thermal diode film is fabricated using two liquid crystal elastomer (LCE) layers separated by an air gap: one surface has a pillar structure, and the other has a hexagonal honeycomb structure. In forward mode, heating the LCE layer with the hexagonal honeycomb structure causes the sidewalls to buckle and contact the pillar structure on the opposite side, facilitating efficient conductive heat transfer. In reverse mode, heating the LCE layer with a pillar structure causes it to contract, increasing the gap between the layers with the pillar and hexagonal structures. This increased gap reduces convective heat transfer across the air gap. The thermal contact asymmetry, depending on the direction of heat flow, enables the film to achieve a thermal rectification ratio of approximate to 2.0 over a wide temperature range of 60-100 degrees C.