New flexible aerogels and xerogels derived from methyltrimethoxysilane/dimethyldimethoxysilane co-precursors

Gen Hayase, Kazuyoshi Kanamori, Kazuki Nakanishi
2011 Journal of Materials Chemistry  
Highly flexible aerogels have been obtained from methyltrimethoxysilane (MTMS) and dimethyldimethoxysilane (DMDMS) 5 co-precursor systems with surfactant n-hexadecyltrimethylammonium chloride (CTAC) to control phase separation in a 2-step acid/base sol-gel reaction. Since first prepared in 1931, 1 aerogels have been synthesized with various chemical compositions such as inorganic oxides (e.g. silica, alumina and titania) 2-4 , organic crosslinked polymers (e.g. resorcinol-formaldehyde (RF)) 5,6
more » ... and biopolymers (e.g. cellulose and chitosan). 7, 8 In all cases, wet gels are typically prepared via liquid-phase processes and dried using a supercritical fluid such as carbon 10 dioxide. Silica aerogels derived from tetraalkoxysilane or water glass are most extensively investigated because they have outstanding properties such as high optical transparency (> 90 %), low refractive indices (< 1.01), low thermal conductivity (< 0.02 W/mK at ambient pressure), good acoustic insulation abilities, and low dielectric constants due to their dilute nano-sized frameworks with high porosities. 2 These features have been applied to multiple fields such as heat insulators, low-k materials for semiconductor devices, stardust capturers for space exploration and catalyst supports. 4,9 However, since their mechanical strength is too low even against a small applied stress, 15 the porous structure is easily collapsed and a drying gel body will exhibit shrinkage and cracks. Supercritical drying, which avoids networks collapsed by capillary force, is hence required to obtain dried aerogels. 2 This process, which needs a special condition such as high pressure and high temperature, prevents aerogels from extended applications. In recent years, there are some reports on improvements of mechanical properties. 10 One promising way is to use organoalkoxysilanes with small organic substituent groups such as methyl group to obtain organic-inorganic hybrid aerogels, but these aerogels are usually opaque because of phase separation of 20 15 Notes and references
doi:10.1039/c1jm13664j fatcat:6k7as5zbgbgb3ban7r5apbwllm