A switchable hydrophilicity solvent mediated process to prepare fine silica aerogel powder as an excellent flatting agent

Abstract

This work demonstrates a facile two-step method to produce fine silica aerogel powder from silica hydrogel by using N,N-dimethylcyclohexylamine (CyNMe2) as a CO2-mediated switchable hydrophilicity solvent. The solvent can almost be totally recycled. More than 70% pore water from silica hydrogel was removed by a quick CO2 reaction with CyNMe2 to form a water miscible phase. The silica cake was then dried under ambient pressure with assistance of ethyl acetate as an azeotropic agent. The N2 adsorption-desorption analysis showed that, the as-prepared silica aerogel powder from a typical hydrogel had a BET surface area of 507.8 m2/g, BJH pore volume of 2.6 cm3/g, and an average pore size of 29.1 nm. The pore volume as well as a narrow particle size distribution (D50 = 6.7 μm) significantly affected the application of the as-produced silica aerogel powder as a flatting agent (FA). Film transmittance index was additionally applied for comparison of the transparence of the applied FA beside the normal extinction index as the performance index. The extinction indices of 61.7 and 52.8% and film transmittance indices of 78.3 and 86.1%, separately for both hydrophobic and hydrophilic applications were measured, hence revealing excellent performance of the as-produced silica aerogel powder.