Classification on the Basis of Interaction Between Different Phases
Depending on the nature of interaction between disperse phase and dispersion medium, colloids are classified as follows.
- Lyophilic colloids: In the case of lyophilic colloids, the disperse phase has great affinity for dispersion medium. In such cases the disperse phase does not easily get precipitated and the colloids are quite stable. The solids obtained after evaporation of the medium can be easily brought back to the colloidal state by shaking the solids with the dispersion medium. Such colloids are thus reversible. Examples of lyophilic colloids are gum, gelatin, starch, proteins, and certain polymers in organic solvents. If water is used as the dispersion medium, the colloid is called hydrophilic colloid.
- Lyophobic colloids: In the case of lyophobic colloids, the disperse phase has little affinity for the dispersion medium. These sols are relatively less stable. They can be easily precipitated by the addition of small amount of electrolyte. Once the sol is precipitated, it cannot be easily brought back to the colloidal state. They are thus irreversible. Examples of lyophobic sols are gold sol and sulphur sol. If water is used as the dispersion medium, the sol is called lyophobic colloid.