On the basis of interaction or affinity of phases, a colloidal solution is classified as lyophilic and lyophobic.
i. Lyophilic colloids:
- A colloidal solution in which the particles of dispersed phase have a great affinity for the dispersion medium are lyophilic colloids.
- If the lyophilic sol is evaporated, the dispersed phase separates. However, if it is remixed with the medium, the sol. can be formed again and hence, such sols are called reversible sols.
- They are stable and difficult to coagulate.
ii. Lyophobic colloids:
- Colloidal solution in which the particles of the dispersed phase have no affinity for the dispersion
medium are called lyophobic colloids.
- The common examples are Ag, Au, hydroxides like Al(OH)3 , Fe(OH)3 , metal sulphides.
- Once precipitated or coagulated they have little tendency or no tendency to revert back to colloidal state.
[Note: Lyo means liquid and philic means loving whereas phobic means fearing and hence liquid hating. If water is the dispersion medium, the terms hydrophilic and hydrophobic are used.]
