Boosting thermal energy transport across the interface between phase change materials and metals via self-assembled monolayers.

Thermal energy storage using phase change materials has great potential to reduce the weather dependency of sustainable energy sources. However, the low thermal conductivity of most phase change materials is a long-standing bottleneck for large-scale practical applications. In modifications to increase the thermal conductivity of phase change materials, the interfacial thermal resistance between phase change materials and discrete additives or porous networks reduces the effective thermal energy transport. In this work, we investigated the interfacial thermal resistance between a metal (gold) and a polyol solid-liquid phase change material (erythritol) at various temperatures including temperatures below the melting point (300 and 350 K), near the melting point (390, 400, 410 K, etc.) and above the melting point (450 and 500 K) adopting non-equilibrium molecular dynamics. Since the gold-erythritol interfacial thermal conductance is low regardless of whether erythritol is melted or not (<40 MW m-2 K-1), self-assembled monolayers were used to boost the interfacial thermal energy transport. The self-assembled monolayer with carboxyl groups was found to increase the interfacial thermal conductance most (by a factor of 7-9). As the temperature increases, the interfacial thermal conductance significantly increases (by ~50 MW m-2 K-1) below the melting point but decreases little above the melting point. Further analysis revealed that the most obvious influencing factor is the interfacial binding energy. This work could build on existing composite phase change material solutions to further improve heat transfer efficiency of energy storage applications in both liquid and solid states.