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Optimization of instantaneous solvent exchange/surface modification process for ambient synthesis of monolithic silica aerogels

2008; Elsevier BV; Volume: 322; Issue: 1 Linguagem: Inglês

10.1016/j.jcis.2008.02.060

1095-7103

Sungwoo Hwang, Tae Youn Kim, Sang‐Hoon Hyun,

Silicone and Siloxane Chemistry

The instantaneous solvent exchange/surface modification (ISE/SM) process for the ambient synthesis of crack-free silica aerogel monoliths with a high production yield was optimized. Monolithic forms of silica wet gels were obtained from aqueous colloidal silica sols prepared via the ion exchange of sodium silicate solutions. Crack-free silica aerogel monoliths were synthesized via an ISE/SM process using isopropyl alcohol/trimethylchlorosilane as a modification agent and n-hexane as a main solvent, followed by ambient drying. The optimum process conditions of the ISE/SM process were investigated by clarifying the reaction mechanism and phenomena. Most effective ranges of process variables on the ISE/SM stage were determined as 0.2500–0.3567 of TMCS/H2O (pore water) in molar ratio and 15–30 of n-hexane/TMCS in volumetric ratio, with a reaction temperature below 283 K. Crack-free silica aerogel monoliths synthesized via these conditions had a well-developed mesoporous structure and excellent properties (bulk density of 0.12–0.14 g/cm3, specific surface area of 724 m2/g), and a high yield (nearly 80%).