Equilibrium gel
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Equilibrium gel is made from a synthetic clay. Unlike other gels, it maintains the same consistency throughout its structure and is stable, which means it does not separate into sections of solid mass and those of more liquid mass. Equilibrium gel filtration liquid chromatography is a technique used for the quantitation of ligand binding.[1][2]
The gel is created by suspending synthetic clay in water. The initial fluid transformed into gel after a few months with concentrations of up to 1% clay by weight. After three years the substance separated into two phases. One phase was clay-rich while the other was clay-poor. However, at concentrations above 1% no such phase separation occurred. Unlike the lower concentrations where the arrangement of clay particles was continually in flux, the particles above 1% concentration locked into a stable structure which is known as equilibrium gel.[3]
Clay particles interact in an anisotropic way differing from the typical isotropic way of colloidal particles, which normally interact with all of their nearest neighbors when forming a gel. The clay particles are disc-shaped giving them an asymmetric charge distribution with a net positive charge on their edges and net negative on their faces. This doesn't allow them to interact with their neighbors, and they tend to form T-bonds. This lets clay particles connect in a chain and allows the gel to form at a low density.[4][5]