Polydopamine-Mediated Silver and Nickel Metallization of Phase Change Microcapsules for Multifunctional Flexible Epoxy Composites

This work reports an environmentally friendly method to metallize phase change material (PCM) microcapsules with thin silver or nickel coatings, using polydopamine (PDA) as a bioinspired adhesion promoter, and their incorporation into flexible epoxy matrices to produce composites with enhanced thermomechanical properties. Commercial paraffin microcapsules were first coated with an ultrathin PDA film via a simple wet chemical process, followed by electroless metallization. Silver treatment produces a discontinuous, cluster-like coating with minimal mass addition (2 wt%), preserving 98% of the original phase change enthalpy (222 J/g vs. 225 J/g for neat PCMs) while maintaining excellent interfacial adhesion with the epoxy matrix. Nickel treatments create more uniform, continuous coatings with progressively higher mass addition (15 and 28 wt% for 2- and 8-min treatments, respectively), resulting in remarkable thermal diffusivity enhancement (from 0.22 to 0.42 mm2/s for powder beds at room temperature) but reduced matrix adhesion due to shielding of the chemically active PDA layer. The phase change capability is successfully preserved across all treatments, with melting/crystallization temperatures remaining stable around 45°C/32°C. When incorporated into flexible epoxy, metallized PCMs provide increased diffusivity and heat storage, retaining mechanical strength and deformability, with strain at break values of 20%–60%. These results establish the considerable potential of metallized PCM microcapsules as multifunctional fillers for advanced thermal management applications in electronics, thermal interface materials, and smart thermoregulating packaging.