Preparation Of Flexible Monolithic Silica Aerogel By Ambient Pressure Drying

In order to synthesize monolithic silica aerogel via ambient drying method, tetraethoxysilane (TEOS), methyltrimethoxysilane (MTMS),3-aminopropyltriethoxysilane (APTES),1,6-bis (Trimethoxysilyl) hexane (BTMSH), hexamethyldisilane(HMDZ) and trimethylchlorosilane (TMCS) were chosen as precursor, co-precursor or modifying agent to synthetize porous monolithic silica aerogel followed with a series of characterization.The research was carried out by sol-gel method; titanium was introduced into system to prepared monolithic silica aerogels with supercritical drying method. It was observed that the content of titanium can affect the microstructure of silica aerogel and the more the amount, the shorter the gelation time is. Styrene monomer was in-situ introduced into the gel skeleton. By changing the reaction condition to carry out polymerization process, the final polystyrene and silica aerogel composite was observed to improve the strength by sacrificing density. Polyurethane sealed with 3-aminopropyltriethoxysilane, which was prepared by diphenylmethane diisocyanate (MDI), polyethylene glycol (PEG) and APTES, was introduced into gel structure as co-precursor to prepared polyurethane and silica aerogel composite. Hybrid silicon precursors of BTMSH and MTMS were used to synthesize silica aerogel, it was found that the transparency increase with the molar ratio of BTMSH/MTMS. What’s more, glass fiber and sol was mixed to prepared monolithic silica aerogel composite via ambient pressure drying method.The effect of gelation and aging temperature on the properties silica aerogels prepared with different methanol/MTMS mole ratio was also studied. It was observed that when the mole ratio was higher to 32, phase separation phenomenon occurred. When the mole ratio was lower to 10, porous network with high crosslinking degree and smaller pore diameter was formed, resulting giant stress and shrinkage. When the mole ratio was about 28, flexible and monolithic silica aerogel can be prepared. The higher the gelation temperature is the better integrity the gel will have. The increase of aging temperature can also improve the integrity of silica aerogel to some extent.In order to synthesize flexible and monolithic silica aerogel with the methanol/MTMS mole ratio lower than 10, N,N-dimethylformamide (DMF) was introduce into the system as drying control chemical additive. The use of DMF was found to be effective in obtaining MTMS based silica aerogels in terms of excellent monolithic property, hydrophobicity and elasticity. The aerogels were produced by hydrolysis and condensation of methanol diluted MTMS in presence of ammonia catalyst followed by ambient drying. It has been observed that higher DMF/MTMS value leads to lower density and higher porosity of aerogels with excellent hydrophobicity. The monolithic and elastic aerogels which can recover to their original shapes after compression were obtained. What’s more, the sample has good hydrophobic property; the contact angle is more than 130°. It can float on the water and `mm air film was formed at the interface if the silica aerogel was immersed in water.