This study explores the impact of pore volume distribution on the structural, thermal, and mechanical properties of spinodal phase-separated silica gels synthesized with poly(ethylene oxide) as a phase-separating agent. By systematically varying gelation temperatures between 20 and 60 °C, we investigate how reaction kinetics influence the resulting pore architecture, thermal conductivity, and elasticity. Nitrogen sorption, mercury intrusion porosimetry, and SEM analysis reveal a transformation from a bimodal pore structure at low temperatures, featuring interconnected macropores, to a predominantly mesoporous network with loss of bimodality. This shift in the diameter of the macropores significantly impacts the thermal insulation properties of the gels as thermal conductivity decreases from 68 to 27 mW (m·K)⁻¹ due to reduced macroporosity, enhanced mesoporosity, and the Knudsen effect. Mechanical testing revealed a substantial decline in Young’s modulus with increasing gelation temperature. These changes are attributed to the interplay of mesoscale structural differences and density variations, driven by increasing gelation temperatures. While higher temperatures lead to reduced strut thickness and the loss of interconnected macropores, the substantial decline in Young’s modulus highlights the critical role of mesoscale structural integrity in maintaining mechanical stability. The findings underscore the importance of an optimized pore volume distribution in tailoring pore structure and performance characteristics, providing a pathway for optimizing silica gels for applications in thermal insulation, filtration, and catalysis.

²⁹Si MAS NMR, Raman spectroscopy and hyperpolarized¹²⁹Xe NMR reveal the post-synthetic modification of porous glass. The grafting, the effect on the pore structure and the identity of the immobilized species are investigated.

The impact of gelation temperature and starting composition (solvent, silica, and polymer content) on the pore structure of silica xerogels with bimodal meso‐/macropore structure is explored. Using statistical regression models, precise control over the pore structure is demonstrated, a challenge in previous studies. Higher gelation temperatures and increased polyethylene oxide (PEO) content enhance the mesopore volume, while higher solvent content and reduced polymer content increase the macropore volume. The ratio of mesopore to macropore volume can be effectively adjusted, facilitating the design of xerogels with tailored properties. These findings optimize silica xerogels with bimodal pore structure for applications in catalysis, thermal insulation, and other advanced technologies.

The thermal conductivity and mechanical strength of porous materials are critically influenced by their internal architecture. Beyond the total porosity, the hierarchical arrangement of pore sizes governs whether heat transfer is dominated by continuum conduction or Knudsen effects, and whether the solid network can efficiently carry mechanical loads. Despite this recognized importance, the specific contribution of mesopores within a macroporous scaffold has remained unclear. In this study, we systematically investigate the role of a secondary mesopore system in hierarchically structured silica xerogels. By combining controlled sol-gel synthesis with polymer-induced phase separation and subsequent calcination, we generate bimodal monoliths with tailored mesopore volumes and structurally comparable macroporous frameworks. Selective reduction of mesopores at 950 °C yields macropore-dominated reference samples, enabling direct assessment of mesoporosity effects. Morphological analysis confirms that mesopore reduction leads to densification within the silica struts, accompanied by moderate macropore shrinkage but preservation of the overall network geometry. Thermal conductivity measurements reveal a pronounced decrease of up to 53% with the addition of mesopore volume, attributed to enhanced Knudsen scattering. In contrast, compressive strength correlates positively with bulk density and inversely with mesoporosity, indicating a trade-off between insulation performance and mechanical stability. A power-law relationship between strength and density is observed, modulated by pore hierarchy. These findings demonstrate that mesoporosity is a powerful yet nuanced design parameter in silica-based monoliths, enabling functional tuning of heat transport and structural integrity. The insights presented here provide a quantitative foundation for the targeted design of advanced thermal insulation materials with application-specific property profiles.