Mitigating supercooling in microencapsulated phase change materials by incorporating compatible polyethylene wax as a nucleating agent

Abstract

Microencapsulated phase change materials (MicroPCMs) have been investigated as thermal storage materials for decades, due to their benefits in storage container protection and PCM leakage prevention. For improved thermal storage properties, the elimination of supercooling, where the micro-sized PCMs crystallize at temperatures significantly below their designated melting point, or over a broad temperature range, has been targeted in many researches. However, most successful methods either compromise the protective shell or reduce the storage enthalpy. In this work, a relatively high-melting-point polyethylene wax (PE-W) that exhibits good compatibility with PCM n-octadecane (n-Oct) was introduced to mitigate the supercooling. MicroPCMs containing n-Oct core materials incorporated with PE-W, were prepared using emulsion polymerization, resulting in cross-linked shell poly(methyl methacrylate-co-allyl methacrylate) denoted as P(MMA-co-AMA). The MicroPCMs with PE-W present consistent sizes ranging from 1 to 5.5 μm, maintained a regular spherical shape, and retained uniform morphologies. The quantity incorporated is exceptionally minimal, constituting merely 2.5 ‰, owing to the effective dispersion, which arises from their intrinsic compatibility. The addition of PE-W nucleating agent significantly reduced the degree of supercooling from 8.0 °C for reference MicroPCM to 1.7 °C for MicroPCM with PE-W. Additionally, the enthalpy associated with heterogeneous nucleation saw a substantial increase, rising from 0% in the reference MicroPCM to 58% in that containing PE-W. The heat resistance of MicroPCM encapsulated by P(MMA-co-AMA) has been greatly improved by 90 °C. The endurance of the MicroPCM highlights the remarkable durability and the sustained effectiveness of PE-W in eliminating supercooling over 100 heating and cooling cycles. Furthermore, in a thermal load scenario, the MicroPCM demonstrated exceptional thermal storage and protective characteristics. The outstanding thermal energy storage properties make them promising candidates for use in textiles, preservation, and transportation applications.