Weather-Resistant Thermoresponsive UV-Curable Smart Window Composites Based on Paraffin Particles.

Thermoresponsive composites made from phase change material particles embedded in polymer matrices show great promise for regulating sunlight transmittance in smart windows. However, their current performance is hindered by critical limitations. Composites obtained from water-soluble matrices present excellent optical performance, but they exhibit intrinsic poor weathering resistance, as they swell and dissolve upon water exposure (e.g., during rainfall or cleaning with aqueous solutions). In contrast, those prepared from water-resistant curable polymers typically require expensive or custom-made phase change materials, and very often show undesired optical properties (e.g., opaque states at room temperature or below). To address this challenge, in this work we developed novel thermoresponsive composite films comprising readily available paraffin particles dispersed within a cross-linked, water-insoluble acrylate matrix. The resulting materials exhibit excellent resistance to water while preserving the characteristic smart window behavior of paraffin-polymer composites; i.e., they remain transparent at low temperatures due to refractive index matching between the matrix and the solid paraffin particles, and become opaque once this condition is lost upon thermally induced paraffin melting, enabling efficient modulation of solar heating gain. In addition, because paraffin-acrylate films are produced via photopolymerization, they are obtained in a fast, straightforward and scalable manner. These features, combined with their low cost, mechanical flexibility, and multistimuli-responsive behavior, make paraffin-acrylate composites a robust and scalable platform for next-generation smart window technologies.