title: Optimization of instantaneous solvent exchange/surface modification process for ambient synthesis of monolithic silica aerogels.
abstract: 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%).
authors.affiliation: School of Advanced Materials Science and Engineering, Department of Ceramic Engineering, Yonsei University, 134 Shinchon-dong, Seodaemun-Gu, Seoul 120-749, South Korea.
authors.forename: Sung-Woo
authors.initials: SW
authors.lastname: Hwang
authors.forename: Tae-Youn
authors.initials: TY
authors.lastname: Kim
authors.forename: Sang-Hoon
authors.initials: SH
authors.lastname: Hyun