Coagulation can be caused by the following methods:
By electrophoresis:
In electrophoresis, the particles of dispersed phase move towards oppositely charged electrode and get neutralized. If the process is continued for sufficient time, these neutral particles unite and grow in size and settle down.
By mutual precipitation:
Mutual precipitation is a process in which oppositely charged sols are mixed in proper proportions to neutralize the charges of each other causing coagulation of both the sols. For example: if positively charged arsenious sulphide sols are mixed, both the sols get coagulated.
By prolonged dialysis:
The stability of a colloidal sol is due to presence of a small amount of the electrolyte. On prolonged dialysis, the electrolyte is completely removed. As a result, the colloidal sol becomes unstable and gets coagulated.
By heating or cooling:
In some cases, heating the sol results into coagulated e.g. coagulation of butter. Similarly, in some cases, cooling the sol results in coagulation e.g. coagulation of milk i.e. on cooling milk, fats start floating on the surface.
