Tailoring Elastic Properties of Silica Aerogels Cross-Linked with Polystyrene

Abstract

The effect of incorporating an organic linking group, 1,6-bis(trimethoxysilyl)hexane (BTMSH), into the underlying silica structure of a styrene cross-linked silica aerogel is examined. Vinyltrimethoxysilane (VTMS) is used to provide a reactive site on the silica backbone for styrene polymerization. Replacement of up to 88 mol % of the silicon from tetramethoxyorthosilicate with silicon derived from BTMSH and VTMS during the making of silica gels improves the elastic behavior in some formulations of the cross-linked aerogels, as evidenced by measurement of the recovered length after compression of samples to 25% strain. This is especially true for some higher density formulations, which recover nearly 100% of their length after compression to 25% strain twice. The compressive modulus of the more elastic monoliths ranged from 0.2 to 3 MPa. Although some of these monoliths had greatly reduced surface areas, changing the solvent used to produce the gels from methanol to ethanol increased the surface area in one instance from 6 to 220 m(2)/g with little affect on the modulus, elastic recovery, porosity, or density.

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

“…2c as a function of density (r). The data follows a power law Y f r 2.6 , which is within the range of exponents measured for native silica aerogels (between about 2.4 and 3.7) [18e20], but lower than the exponents measured for crosslinked aerogels (between about 3.9 and 5) [21,22]. To explain this discrepancy, we note that power law relationships between modulus and density depend strongly on the connectivity between particles [21e23].…”

Elastic Behavior of Methyltrimethoxysilane Based Aerogels Reinforced with Tri-Isocyanate

“…Note that this analysis is typically performed for experiments in tension loading, and direct comparisons to other systems outside this study should be made with caution. Empirical models for toughness for nonreinforced (standard error ) 0.69, r 2 ) 0.92) and reinforced aerogels (standard error ) 0.35, r 2 ) 0.99) are shown in Figure 10 graphed vs total Si concentration and mol fraction BTMSPA for acetone prepared samples (Figure 10a) and for acetonitrile prepared samples (Figure 10b) (20). Polymer reinforced samples made using 80 mol % Si derived from BTMSPA show up to an order of magnitude increase in toughness over nonreinforced samples of the same composition.…”

Flexible aerogels with interpenetrating network structure of bacterial cellulose–silica composite from sodium silicate precursor via freeze drying process

“…1,6-bis(trimethoxysilyl)hexane] into the silica skeleton to reduce the Si-O-Si bonds followed by the conformal coating of polymer. 19 Both the exible links and the isotropic coating endow the aerogels with outstanding exibility and recovery (they recover nearly 100% of their original size aer compression to 25% strain twice). However, they pointed out that the preparation process was fairly involved, and the method of conformally coating the silica gel skeleton with a polymer was required to be streamlined to adapt to commercial scale manufacturing.…”