What is the difference between lyophilic and lyophobic colloids?

This is a very common exam topic. Let’s break it down point-wise:

Lyophilic Colloids (Solvent-loving)

1. Definition – Colloids in which dispersed particles have a strong affinity for the dispersion medium.
2. Formation – Readily formed by direct mixing (self-formation is easy).
3. Reversibility – Reversible sols → if dried, they can be reconstituted by simply adding the dispersion medium.
4. Stability – Very stable because the medium strongly binds with dispersed particles.
5. Electrolyte effect – Not easily coagulated by electrolytes.
6. Examples – Gum, starch, gelatin, proteins in water.
7. Properties – High viscosity, show Tyndall effect, and are hydrated/solvated.

Lyophobic Colloids (Solvent-hating)

1. Definition – Colloids in which dispersed particles have little or no affinity for the dispersion medium.
2. Formation – Not easily formed; usually prepared by special methods (e.g., chemical reactions, electrical dispersion).
3. Reversibility – Irreversible sols → once dried, they cannot be easily reconstituted.
4. Stability – Less stable; require stabilizing agents to prevent coagulation.
5. Electrolyte effect – Easily coagulated/precipitated by small amounts of electrolytes.
6. Examples – Sols of metals (Au, Ag), metal sulfides (As₂S₃, Sb₂S₃).
7. Properties – Lower viscosity, no strong solvation.

In short:

• Lyophilic colloids = solvent-loving, stable, reversible (e.g., starch, gum).
• Lyophobic colloids = solvent-hating, unstable, irreversible, need stabilizers (e.g., metal sols).