The Formation and Collapse of Mixed Monolayer of Triolein and Tricaprylin

Abstract

Abstract The surface pressure-area curves of mixed monolayers of triolein and tricaprylin and the equilibrium spreading pressures of these liquid mixtures were measured at 25 °C. The surface pressures of the monolayers of the pure components, triolein and tricaprylin, did not vary when the monolayer was compressed below its collapse area, but the surface pressure of their mixed monolayers increased with the compression; the surface pressure at a zero area agreed well with the value of the equilibrium spreading pressure. From the two curves, the one representing the relation between the collapse pressure and the composition of the mixed monolayer, and the other representing the relation between the equilibrium spreading pressure and the composition of the liquid mixture, the compositions of the mixed monolayer and the liquid mixture coexisting in the equilibrium were obtained. Consequently, it was found that the component whose collapse pressure was lower was richer in the liquid mixture than in the mixed monolayer, while the other component, whose collapse pressure was higher, was poorer in the liquid mixture than in the mixed monolayer. It was concluded, on the basis of the phase rule and thermodynamics for a plane interface, that triolein and tricaprylin form a regular mixture in the monolayer as well as in a liquid.