Manipulation of pore size distributions in silica and ormosil gels dried under ambient pressure conditions

Sol-gel derived silica and organically modified silica gels were solvent-exchanged and dried from various solvent mixtures in order to control the magnitude of capillary stress imposed on the gel, and to limit shrinkage during the drying process. A collection of trends was identified in the evolution of porosity, pore size distributions, and surface area of gels dried from various alcohols and acetone/alkane mixtures. By selecting n-alcohols of increasing length from 2 to 5 carbon units, the average pore size of silica gels was adjusted systematically from 4.1 to 3.1 nm with a relatively narrow pore size distribution. The use of acetone/alkane mixtures to modify the capillary stresses that are experienced by drying gels was demonstrated to be effective in controlling pore size and pore volume at high fractions of alkane. Ambient pressure drying thus provides an efficient method of porosity control in materials derived from the sol-gel process. (C) 2002 Elsevier Science B.V. All rights reserved.