Hydrophobic silica-shelled shape-stabilized phase change materials for durable, leakage-resistant cementitious mortars

Shape-stabilized phase change materials (SSPCMs) are promising for thermally functional mortars, but slight leakage during mixing and phase transition can degrade the particle–matrix interface and reduce durability. This study developed a surfactant-free interfacial self-assembly route to build a hydrophobic silica shell on diatomite/ n -hexadecane SSPCM particles. The shell increased the particle contact angle from 112.1° to 140.2° and reduced leakage to 0.12% after 4 h at 60 °C. At equal PCM dosage, the shell-modified mortar showed lower water absorption and chloride diffusion and higher compressive strength than mortar with unmodified SSPCM. After 500 thermal cycles between 0 and 40 °C, the shell-modified mortar retained a melting enthalpy of 8.85 J/g with only 1.8% latent-heat loss. Microscopy and nanoindentation indicated a denser interfacial region, showing that a simple mineral shell can improve thermal-storage mortar reliability for building applications.