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Sufficient shape stability is essential for a high-performance phase change material (PCM). Although significant advances have been made to develop form-stable composites, technical development in the field of polymer-based PCMs is currently limited by an incomplete understanding of the shape stability. Form-stable polyethylene glycol/acetylene black (PEG/AB) PCMs containing PEGs with different average molecular weights have been obtained by melt mixing to investigate the shape stability of the PEG/AB composites. It was found that the phase change behaviors of the PEG/AB composites were not only attributed to the interactions between the AB and PEG, but also to the intermolecular interactions of the PEG chains, depending on the varying molecular weights of the PEGs. Physically crosslinked structure with temporary junctions was formed through hydrogen bonding, capillary, surface tension forces, intermolecular friction, and macromolecular entanglement, which contributed to the constrained chain motion and thus the solid-solid phase change behavior of the PEG/AB composites. The physically crosslinked structure was more stable with longer length of the PEG molecular chains, resulting in higher critical impregnated contents of the PEG into the AB and thus improved latent heat.

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Dielectric materials with thermally responsive property are being pursued in fields such as next-generation sensors, smart switches, and novel actuators. These applications require that the dielectric materials have mechanical durability and stable serviceability besides thermally responsive dielectric behavior. Herein, we report a novel thermally responsive, mechanically durable, and low-cost dielectric composite simply fabricated by vacuum impregnating polyethylene glycol (PEG) into kapok fiber and compounding them with polyvinylidene fluoride. A remarkable dielectric susceptibility, controlled dielectric transition temperature, and obvious thermal hysteresis of the composite films induced by the solid-liquid phase transition of PEG are demonstrated. The effect of molecular weights of PEG on the dielectric response behaviors is evaluated. Such thermally responsive dielectric materials with satisfactory mechanical durability will offer a chance toward constructing thermally responsive systems for reliable and stable operation.