Interfacial tension.

• It is the force operating along the surface of separation between two insoluble or sparingly soluble liquids.
• Conceptually it is equivalent to the surface tension.

e.g, In a heterogeneous colloid solution like protein in water, protein represent a phase which is different from that of water because protein is not soluble in water. So a surface of separation will be observed between protein and water exerting interfacial tension between these two phases.