Tailoring structure property relationships and elastic phenomenon in native and polymer reinforced silica aerogels

The focus of this work was to study the effects of flexible silica backbones on elastic properties of silica aerogels. Two routes were examined. In the first, alkyl-chain bis-silanes were used in conjunction with tetraethoxysilane (TEOS) precursor to obtain silica aerogel backbones which were later reinforced by epoxy. The alkyl-chain bis-silanes at 15 mol % concentration were found to increase the elastic recovery from a state of 25% compressive strain significantly compared to traditional formulations without bis-silane. It was noted that a reduction in modulus was observed with aerogels containing bis-silane. The length of the alkyl-chain was observed to have no appreciable impact on the elastic response of the aerogels, or other material properties such as density or surface area. Finally, an amine functionalized bis-silane was demonstrated to exhibit elastic behavior while maintaining increased reinforcement.The second approach examined the effect of reducing the silica network connectivity on elastic response. For this purpose, a bifunctional silane, dimethyldiethoxysilane (DMDES), was substituted for a part of the tetrafunctional TEOS in the silane formulation. It was found that low concentrations, DMDES helped increase elastic response, but reduced the modulus. Higher concentrations of DMDES did not result in further enhancement of elastic response.