ABSTRACT
I t is difficult to provide a clear-cut definition of a gel. In general, gels are characterized by a preponderance of solvent and the presence of a three-dimensional network of connected molecules or particles, at least over the time scale considered. Rheologically, they are characterized by a predominantly elastic behavior over the time scale considered and a modulus that is relatively small (generally <107 Pa) compared with real solids (generally 109-1011 Pa). Various types of gels can be distinguished, where the precise division may depend on the criteria used.
