Surface active inverse micelles

Surface tension of solutions of a commercial non-ionic surfactant, Laureth 4, and two hydrocarbons, decane and hexadecane, with added water, was determined using a de Nouy ring. The results showed a reduction of surface tension with added water, confirming an earlier suggestion of surface activity of inverse micelles. The surface activity is ascribed to the orientation of the hydrocarbon chains in the inverse micelle, giving a preferential location of the low surface free-energy methyl groups at the surface of the micelle. The location of the micelle at the surface was estimated from calculations of the minimum in the free energy when a solid particle was transferred across the liquid–air interface. This energy showed a distinct minimum indicating the location of the particle. However, the conditions for that minimum to occur were such that no balance of surface tension forces along the liquid surface to air could occur. The reason for that apparent discrepancy is discussed.