Green preparation and performance research of n-octadecane@silica phase change microcapsules for building energy conservation

Abstract

The synthesis of microencapsulated phase change materials (MPCMs) was accomplished via a green, low-temperature (45 ℃), low-shear (800–1000 rpm) interfacial sol–gel process, a method that circumvents the utilisation of strong acids and bases. These MPCMs are constituted of silica shells and n-octadecane cores. Utilising an optimised SDS/CTAB emulsifier system, uniform spherical microcapsules with a main diameter of 0.81 μm were obtained. The optimised MPCM2 exhibited high latent heat (ΔH_m 124.9 ± 0.8 J/g; ΔH_c 126.1 ± 1.2 J/g) with an encapsulation efficiency of 56.9 ± 0.4 %, whilst thermogravimetry showed the decomposition onset increased to 185.2 °C relative to neat n-octadecane (119.4 °C). Following 500 thermal cycles, enthalpy attenuation was recorded at only 1.2 %, thereby confirming excellent durability. When incorporated into cement boards at a 20 wt% loading, MPCM2 demonstrated a 41.14 % reduction in thermal conductivity and a 21.9 % decrease in temperature fluctuation when subjected to repetitive cycling between 5 and 120 °C (γ=0.781). No leakage or discernible chemical interaction with the matrix was observed, as substantiated by FT‑IR, XRD and SEM‑EDX analysis. The cementitious microstructure remained intact, with well-dispersed microcapsules, and compressive strength was maintained when 20 wt% MPCM2 was combined with 20 wt% quartz sand. The findings of this study demonstrate an environmentally benign approach to the fabrication of high-performance MPCMs, thereby validating their efficacy in thermal regulation within cement-based building components.