The Colloidal State

Colloidal systems involve microscopic particles dispersed in a medium, called the dispersion medium or continuous phase.

For instance, when a sodium chloride solution is added to a silver nitrate solution, the resulting silver chloride forms tiny crystals, creating a colloidal system rather than a filterable precipitate.

These colloidal particles, or the dispersed phase, can exist in a solid, liquid, or gaseous state within a dispersion medium.

For instance, sols have a liquid or a solid dispersion medium, while aerosols have a gas dispersion medium. Foams contain either a liquid or a solid dispersion medium. Emulsions and colloidal suspensions have a liquid dispersion medium.

Lyophilic or solvent-loving colloidal systems are thermodynamically stable due to strong solvent-solute interactions. They form spontaneously from the dry bulk material of colloidal particles in the dispersion medium.

But lyophobic or solvent-hating colloids are thermodynamically unstable and may require the presence of adsorbed ions for their stabilization.

Colloidal suspensions with particles greater than 10³ Å will eventually settle down due to gravity, forming noncolloidal suspensions by a process known as sedimentation.