Fabrication of inorganic eutectic salt@SiO2 phase change microcapsules and their influence on mechanical and thermal properties of gypsum-based composites

Phase change materials offer potential for improving building energy efficiency through heat absorption/release during phase transition. This study develops novel inorganic hydrated salt@SiO₂ phase change microcapsules using modified eutectic hydrated salt as the core and a dual-component silica/nanosilica shell via the Pickering emulsion method. These microcapsules were incorporated into gypsum for forming functional composites. Comprehensive investigations were conducted to evaluate the thermal properties of the modified eutectic hydrated salts and the microcapsules, alongside the mechanical properties and thermal management capabilities of the composites. Optimized microcapsule properties: The optimized microcapsules exhibited a rough surface, an average size of 6.3 μm, a phase-change temperature of 21.31°C, and an enthalpy of 286.8 J/g. Remarkably, the enthalpy loss was limited to 0.4 % after 120 heating-cooling cycles. Composite performance: In the gypsum composites, 7-day compressive and flexural strengths peaked at 10.8 MPa and 5.3 MPa (2.0 wt% microcapsules), declining to 6.6 MPa and 3.5 MPa at 4.0 wt%. Infrared thermography confirmed effective thermal buffering: incorporating 4.0 wt% microcapsules reduced surface temperature by 4°C versus the control specimen after 480 s heating. Concurrently, thermal conductivity decreased by 32.8 % (measured at 4.0 wt% content), further enhancing potential for building thermal regulation. By delaying heat transfer through diurnal phase-change cycles, they directly reduce cooling loads in hot climates, enabling significant annual energy savings in air-conditioned buildings and advancing sustainable construction.