Organic-inorganic hybrid aerogels with high mechanical properties via organotrialkoxysilane-derived sol-gel process

Abstract

A brief overview of siloxane-based low-density aerogels and aerogels-like xerogels is presented. Aerogels are highly porous solids composed of inorganic oxides, metals, cross-linked polymers and carbons, and are known to possess a number of excellent physical properties such as high visible-light transparency with low refractive index, low dielectric properties, and extremely-low thermal conductivity. Aerogels are therefore regarded as a promising candidate for applications such as superinsulators; however, a mass production and applications of aerogels have been significantly discouraged due to the lack of mechanical properties since the first invention in 1931. This review introduces the substantial effort to improve the mechanical properties of aerogels with particularly highlighting our recent findings on elastic organicinorganic hybrid aerogel monoliths obtained from methyltrimethoxysilane (MTMS) using the controlled solgel chemistry.

One-dimensional silicone nanofilaments

“…Furthermore, the educt for these aerogels is MTMS that implies a very similar composition compared to 1D-SNF. Besides equivalent educts and products, the similarity of both systems extends to the initially acidic reaction conditions, the hydrophobicity and the elasticity of the obtained products [8,100,101].…”

“…Recently, transparent and elastic aerogels could be synthesised using sol-gel synthesis [100,101]. Under certain conditions, a specific topography of the aerogel, described as 'fibrous skeleton' [101] or 'continuous fibrous network', [100] was obtained.…”

“…Under certain conditions, a specific topography of the aerogel, described as 'fibrous skeleton' [101] or 'continuous fibrous network', [100] was obtained. The structures observed by EM appear very similar to those of 1D-SNF.…”

Transition from transparent aerogels to hierarchically porous monoliths in polymethylsilsesquioxane sol–gel system

“…The PMSQ materials also exhibit unique mechanical properties arising from the lower cross-linking density compared to silica and less-polar methyl groups that repel each other when compressed. Aerogels with PMSQ composition are reported to show ''spring-back'' and bendable features without being broken [25][26][27][28][29][30]. Methylsilsesquioxane-based films (and other organotrialkoxysilane-derived films) for low-k applications also exhibit unique mechanical properties such as decreased elastic modulus, hardness, brittleness and the emergence of viscoelastic properties [31][32][33][34][35][36][37].…”

“…In this research, transitions of pore structures from mesoporous to hierarchical meso/macroporous in PMSQ monolith have been investigated in the sol-gel system containing methyltrimethoxysilane (MTMS), surfactant, and urea [26][27][28][29][30]. This system relies on the hydrolysis of MTMS in weakly acidic media and subsequent polycondensation in weakly basic media.…”