Integrated Silica-Encapsulated Lauric Acid Phase Change Material into Acid-Activated Geopolymer for Thermal Energy Storage Applications.

This paper investigates the development of a sustainable thermal energy storage material for buildings by combining silica-encapsulated lauric acid phase change materials (PCMs) with an acid-activated geopolymer matrix. The study addresses two significant environmental concerns: the high CO2 emissions associated with Portland cement production and the large energy consumption of buildings for heating and cooling. Lauric acid, a biobased fatty acid PCM, was selected as a by-stander because of its high latent heat capacity and suitable melting temperature facilitating encapsulation and leakage characterization. Lauric acid has been encapsulated inside silica (SiO2) shells using a TEOS-based emulsion process. The resulting microcapsules were then integrated into a phosphate-based acid-activated geopolymer, an environmentally friendly alternative to conventional cement. SEM and EDS confirmed the formation of spherical silica microcapsules containing the PCM, with diameters between 15 and 40 μm. FTIR spectroscopy demonstrated successful silica shell formation and preservation of the lauric acid compound, indicating good chemical compatibility with the geopolymer matrix. Thermal analyses showed that the microcapsules contain 49 wt.% of PCM inside 51 wt.% of silica shell and possessed a latent heat of about 80 J/g. Eventually, 17 wt.% of PCM@SiO2 have been incorporated inside the geopolymer, resulted in a latent heat of 16 J/g, corresponding to approximately 9 wt.% PCM. Leakage tests revealed that the silica shells significantly reduced PCM leakage, although complete sealing was not achieved because of shell porosity. Despite this limitation, the geopolymer composite maintained reversible thermal energy storage behavior and showed promising compatibility between the PCM microcapsules and the acid-activated geopolymer matrix.