Gel Point

Abstract The gel point (GP) marks the instant at which a material passes from liquid to solid due to gelation. A material at its GP, commonly called critical gel , is in a critical state with unique physical and chemical properties. Polymer gelation occurs in amorphous materials when its constituents connect internally by chemical or physical bonds to form macromolecular clusters. Gels often assemble from a mixture of different molecular or particular species. The chemical or physical GP is reached when the first macromolecular cluster has grown to infinite size. While the connectivity typically grows slowly during gelation, its reversal may occur rather rapidly. Reverse gelation due to the fluctuation or breakage of internal junctions will cause a gel to pass backwards through GP and, thus, assume its liquid state. GP is important industrially and in biology. Many soft materials, namely in food, pharmaceuticals, photographic media, adhesives, foams, crystallizing polymers, vibration dampeners, super absorbers, proteins, polysaccharides, clotting blood (to name a few), are close to their chemical of physical GP, that is they are liquids just before reaching their GP or they are solids that have barely passed the GP. The universality of the linear viscoelasticity at GP provides a powerful tool for developing new materials and processes.