Xerogels defined

Many of the early physisorption measurements were undertaken on ill-defined silica gels of unknown origin. However, as a result of systematic work on the formation of the hydrogel and its ageing and conversion to the xerogel, it is now possible to control the adsorptive properties within quite narrow limits (Barby, 1976 Her 1979, p. 488 Unger, 1979, p. 196 Kenny and Sing, 1994). 

The dendrons 46-[G ] and 47-[G ] allowed us to obtain another type of hybrid material incorporating dendritic structiues. The co-hydrolysis and polycondensation of these macromolecules with a defined and varying number of equivalents of tetraethoxysilane (TEOS) was carried out via a sol-gel protocol, giving rise to dendrimer-silica xerogels, in which the dendron is covalently linked by one Si-C bond to the silica [54] (Scheme 30). The natiue of the material was determined by solid NMR ( Si, P), thermal analyses, and nitrogen adsorption (BET) measiuements. Some of these materials were found to be mesoporous with a narrow pore size distribution. 

Figure 25.12. Photograph of a xerogel monolith of a Fesorcinol-formaldehyde/ammonium nitrate (3 7 w/w) nanostructured energetic composite illustrating the capability for sol-gel energetic materials to be cast and dried to well-defined shapes.

Sol is defined as small particles dispersed in a medium, while gel is a relatively rigid interconnected network containing different-sized pores connected by polymeric chains. The wet gel can result in a xerogel if the volatile components are... 

---