SOLID AND LIQUID MONOMOLECULAR FILM AT OIL/H2O INTERFACES

Discontinuities in slopes of interfacial tension vs. temperature (γ vs. T) are observed for triglyceride oil H2O systems, the discontinuities being seen when the oil contains low to moderate percentages of certain oil-soluble, water-insoluble surface-active components such as propylene glycol monoester or monoglyceride. It is proposed that such a γ vs. T break involves melting of a monomolecular layer adsorbed at the interface. The large change in slope at the break can be interpreted from the equation ( ∂H ∂A)P,T = γ - T( ∂γ ∂T)P,A with the change in ( ∂H ∂A) at the break corresponding approximately to the heat of fusion of a monolayer. Estimated areas per molecule in the two regions, above and below the break, are of the order 60 A2 and 20 A2, and are thus compatible with the hypothesis. © 1969.