Gels Preparation and Surface Properties

By changing the R/C molar ratio, the microstrnctnre of the polymerized gels and therefore of the final carbon gels can be varied. A low R/C ratio resnlts in polymeric gels, whereas high R/C ratios give rise to colloidal gels. The main reactions between R and F include an addition reaction of F to the 2-, 4-, and/or 

The second stage in the preparation of carbon gels is drying of the wet gel to remove the solvent trapped in its gel strnctnre. The volnme occnpied by the solvent will essentially constitute the meso- and/or macropore network of the 

Subcritical drying can sometimes yield porous xerogels when the gel structure is strong enough to withstand capillary pressures [11,31], although it is not possible to produce carbon xerogels with both small pores and high pore volumes 

The solvent of the wet gel (usually, water) is first exchanged with another organic solvent, such as methanol, ethanol, or acetone. The latter solvent is further exchanged with liquid CO2 (Tc = 304 K and Pc = 7.4 MPa). Once transformed in a supercritical fluid (e.g., at 313 K and 9 MPa), with null surface tension, it can be evacuated from the pore texture of tlie gel without pore collapse. 

Freezing-drying methods give rise to cryogels. In this case, the solvent is frozen and then removed by sublimation, avoiding a vapor-liquid interface 

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