Process of forming a hydrophobic aerogel

A process of forming a hydrophobic aerogel comprising:

• a gelation step of providing a gel having a SiO.sub.2 skeleton structure formed by hydrolysis and condensation of an alkoxysilane compound selected from the group consisting of the following formulae I, II, III and IV:
• ##STR3## wherein each of R.sup.1, R.sup.2 and R.sup.3 is independently a C.sub.1 -C.sub.5 alkyl group;
• R.sup.4 -Si(OR.sup.5).sub.3 (II)
• wherein each of R.sup.4 and R.sup.5 is independently a C.sub.1 -C.sub.5 alkyl group;
• Si(OR.sup.6).sub.4 (III)
• wherein R.sup.6 is a C.sub.1 - C.sub.5 alkyl group;
• and ##STR4## wherein R is independently a C.sub.1 - C.sub.5 alkyl group and n is an integral number;
• a hydrophobic step of reacting said gel in a reaction chamber with a hydrophobic agent selected from the group consisting of organosilanes, carboxylic acids and halogenated alkyl, wherein said hydrophobic agent comprises hydrophobic groups selected from the group consisting of alkyl group, fluoroalkyl group, phenyl group, and a fluorophenyl group as well as functional groups reactive with silanol groups, said functional groups selected from the group consisting of halogens, amino group, imino group, carboxyl group, alkoxyl group and hydroxyl group,
• in the presence of a medium selected from the group consisting of C.sub.1 -C.sub.4 alcohols, carbon dioxide, dichlorodifluoromethane, water and mixtures thereof
• under a supercritical condition based on said medium to form a hydrophobic gel, said hydrophobic agent being introduced into said reaction chamber after said medium reaches supercritical condition;
• and
• a dry step of supercritically drying said hydrophobic gel to remove said medium to obtain said hydrophobic aerogel which is transparent and of a porous structure.