Preparation of high porosity xerogels by chemical surface modification.
OwnerRavindra Deshpande, Douglas M. Smith +1inventors
InventorsRavindra Deshpande, Douglas M. Smith, C. Jeffrey Brinker
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Abstract
This invention provides an extremely porous xerogel dried at vacuum-to-below supercritical pressures but having the properties of aerogels which are typically dried at supercritical pressures. This is done by reacting the internal pore surface of the wet gel with organic substances in order to change the contact angle of the fluid meniscus in the pores during drying. Shrinkage of the gel (which is normally prevented by use of high autoclave pressures, such that the pore fluid is at temperature and pressure above its critical values) is avoided even at vacuum or ambient pressures.
Claims11
The method of producing a xerogel of porosity greater than about 0.6 comprising the steps of:
- a) preparing a wet gel containing water, said gel having a pore fluid contact angle .THETA. and a substantial number of its atoms which are surface species, by at least one process selected from the group of hydrolysis and condensation of metal alkoxides, gelling of particulate metal oxides, and gelation of organic precursors;
- b) exchanging substantially all of the water contained in said wet gel with a protic or aprotic solvent;
- c) reacting said wet gel with a surface modification agent R.sub.x MX.sub.y, wherein R is an organic group, M is selected from the group consisting of Si and Al, and X is halogen, to cause replacement of a substantial number of surface species with a different species which substantially increases the pore fluid contact angle .THETA.;
- and
- d) drying said wet gel at one or more pressures selected to be within the range from vacuum to sub-critical.
Dependencies are inferred from the claim text.