Ultra-soft Thermal Diodes Enabled by Dual-Alkane-Based Phase Change Composites

TL;DR

This paper introduces an ultra-soft phase change material-based thermal diode with high rectification, mechanical compliance, and potential for energy-efficient building temperature regulation.

Contribution

The study presents a novel heterojunction thermal diode made of dual-alkane PCM and polyurethane with record low elastic modulus and high elongation, demonstrating effective thermal rectification.

Findings

Thermal rectification factor up to 1.42

Mechanical compliance with elastic modulus of 0.4 KPa

Potential application in building temperature regulation

Abstract

Thermal diode, a type of device that allows heat to flow in one direction preferentially, can be employed in many thermal applications. However, if the mechanical compliance of the thermal diode is poor, which prevents its intimate contact with heat source or sink surfaces, the thermal rectification performance cannot be used to its full extent. In this work, we introduce a heterojunction thermal diode made of a phase change material (PCM) consisting of dual alkanes (hexadecane and paraffine wax) and polyurethane. The fabricated thermal diode exhibits an ultra soft mechanical feature, with a low elastic modulus of 0.4 KPa and larger than 300% elongation until failure: the best values reported to date for thermal diodes. The measured thermal rectification factor is as high as 1.42 that in line with the theoretical model prediction. Molecular dynamic simulations reveal that the thermal rectification mechanism of the PCM based thermal diode originates from the crystal-amorphous phase transition of the hexadecane terminal as the temperature bias flips. Therefore, the heat flow in the forward direction is greater than the flux in the reverse direction. A series of experiments and finite element analyses are employed to verify the feasibility of thermal diodes for applications. Our results demonstrate that the fabricated thermal diode can be potentially used in building envelop to help with temperature regulation and thus reduce energy consumption for space cooling or heating.