Microstructural Engineering of Porous Polymethylsilsesquioxane via Solvothermal Synthesis in Diverse Solvents

Polymethylsilsesquioxane (PMSQ) aerogel and foams synthesized under solvothermal conditions exhibit a unique combination of structural, mechanical, and functional properties. In this study, we investigated the influence of various solvents, guided by Hansen solubility parameters, along with controlled reaction conditions such as saturated vapor pressure (VP) and temperature, on the particle size distribution, pore structure, and material performance. Porous PMSQ displays low densities (0.07–0.11 g/cm³), high porosity (over 95%), and large pore sizes, resulting in high flexibility and resilience. These properties are particularly suitable for applications where traditional brittle aerogels fall short. Mechanical testing reveals that the interparticle neck structure and particle size distribution play important roles in compression strength and densification behavior, with a trend of smaller particles leading to higher strength and densification. The hydrophobic surface of porous PMSQ, imparted by the methyl groups of the silane precursors, enhances their processing and properties, allowing for consistent performance from ambient pressure drying and enabling applications such as oil–water separation. In addition to mechanical and surface properties, porous PMSQ demonstrates excellent acoustic absorption performance, especially in the low-frequency range below 2000 Hz, with preliminary tests revealing superior absorption compared to polyurethane foams, even at reduced thicknesses. These findings highlight the potential of porous PMSQ materials for use in lightweight, flexible materials for acoustic insulation, oil–water separation, and other advanced applications.