Also called frozen gel. Under certain conditions, the colloidal particles in the sol can be connected to each other to form a spatial network structure. The structural gaps are filled with liquid as a dispersion medium. Regardless of the amount of liquid, this dispersed system that has lost its fluidity is called a gel. Fresh gel is called a wet gel. When the liquid in the gel is completely lost, it is also called a gel, which is a dry gel. The structural gaps of the dry gel are filled with gas.
When the liquid filled in the gaps of the gel structure is water, it is called a hydrogel.
The gel has a certain geometric shape and has the mechanical properties of a solid, such as strength, elasticity and yield value. But from the internal structure, it is different from ordinary solids. It consists of two phases, solid-liquid, and also has some properties of liquids. For example, the diffusion rate of ions in fresh hydrogels is close to the diffusion rate in aqueous solutions. This shows that in fresh hydrogels, both the dispersed phase and the dispersion medium are continuous phases, which is the structural characteristic of the gel.