The de-agglomeration (Deflocculation) or conversion of a solid or semi-solid precipitate into a colloid in presence of an electrolyte by agitation with the solvent or dispersion medium is peptization. In case of physical separation process like ionic separation or filtration some ionic particles bearing same charge repel each other and do not filter so a flocculating agents are added to form a coalesce so that the filtration process is facilitated. And sometimes the formation of coalesce hinders the reaction or a certain unit operation so a peptizing agent is used to convert these precipitate into a colloid or sol.
In a colloid with ionic participants there is bound to be accumulation of charges around a surface plane. The bulk separates the article with a layer of fluid which is electrostatically bound to the dispersed particle. This introduces an electric potential between the dispersed particle and the stationary layer of the bulk fluid separated by the interfacial layer. This electric potential developed is called as zeta potential also called electrokinetic potential given by symbol ∈.
The random motion of the small particles in a solution or colloid which is a consequence of the molecular or atomic average velocity in different directions is called Brownian motion.
NOTE: Why the dust particles in a beam of sunlight from a window move in random?
The discovery of Brownian motion showed that the presence of gas molecules around it causes the random change in its velocity thus giving it random motion and proving the existing of atoms in the atmosphere. Perrin was awarded Noble Prize in 1926 for this work which accounts for discontinuous structure of matter.
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