Influence of silica derivatizer and monomer functionality and concentration on the mechanical properties of rapid synthesis cross-linked aerogels

Abstract

The relationship between both monomer functionality and concentration and the mechanical properties of cross-linked aerogels was investigated. For this, alcogels were synthesized using a gelation solution containing an alkoxide (tetramethyl orthosilicate, TMOS) to form the oxide gel skeleton, trimethoxysilylpropyl methacrylate (MTMS) to attach a coupling acrylic group to the pore walls, an acrylic monomer, a photoinitiator (Eosin Y) and a tertiary amine acting as base catalyst for gelation and as polymerization co-initiator. The gelation solvent was the ethanol–water azeotrope mixture (4.4% water by volume). After gelation, alcogels were cross-linked by photopolymerization using green light and were dried using the ethanol–water azeotrope as a supercritical fluid. Densities, shrinkage, surface areas, pore sizes, moduli and specific energy absorptions of the resulting monoliths were measured and found to depend very strongly on MTMS and monomer concentration and, to a lesser extent, on monomer functionality. Optimization of the gelation solution composition allowed for the fabrication of aerogel composites with Young's modulus of 257 MPa and specific energy absorption of 19.4 J g−1, which makes them possible candidates for ballistic protection applications.