Tuning density and morphology of organic-inorganic hybrid-silica aerogels through precursor dilution for lightweight applications

Abstract

Organic-inorganic hybrid-silica aerogels can be made of ethyltrimethoxysilane (MTMS, CH3Si(OCH3)3) and dimethyldimethoxysilane (DMDMS, Si(OCH3)2(CH3)2) in a typical sol-gel process yielding flexible and hydrophobic structures. In this work, MTMS and DMDMS were condensed with an increasing amount of water, leading to a decrease in the final materials density from ∼ 0.110 g cm-3 down to ∼ 0.066 g cm-3. The gels were synthesized in a one-pot synthesis and dried under ambient pressure conditions at 80°C. While the topology of the network remained intact, the size of secondary particles decreased from roughly 8.2 to 3.3 μm. The inter-particle neck thickness remained unaffected with increasing aging time for higher dilutions. The measured thermal conductivities were all in similar range (∼ 32.5 mW (m K)-1 at 25°C), showing very good insulation characteristics. In general, higher diluted samples exhibited increasing softness and decreasing Young’s modulus, even with increased aging times. Overall, our optimized recipe leads to hydrophobic aerogels with ultralow densities while demonstrating very low thermal conductivity and a flexible mechanical performance.