# Influence of Gelation Temperature on Structural, Thermal, and Mechanical Properties of Monolithic Silica Gels with Mono- and Bimodal Pore Structure

## TL;DR

This study shows how changing the temperature during gel formation affects the structure and properties of silica gels, impacting their thermal and mechanical performance.

## Contribution

The study reveals how gelation temperature alters pore structure and material properties, offering insights for optimizing silica gels for specific applications.

## Key findings

- Lower gelation temperatures produce bimodal pore structures with interconnected macropores.
- Higher temperatures result in mesoporous networks with reduced thermal conductivity and mechanical strength.
- Thermal conductivity decreases from 68 to 27 mW (m·K)−1 with increasing gelation temperature.

## Abstract

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.