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Studies were carried out at the water/air interface on mixed monolayers of a macromolecular substance with ionizable polar groups and a "horizontal" interface orientation, poly-2-vinylpyridine, and three lowmolecular-weight substances with a "vertical" orientation, stearic acid, methyl stearate and stearylamine, at 15 ~ 25 ~ and 35 ~ The surface areas, collapse pressures and compressibility coefficients as a function of mole ratios showed compatibility between the components for all three twocomponent systems. The values of the enthalpy and entropy contributions to the free surface energy of mixing were found to be positive for the poly-2-vinylpyridine/stearic acid system and negative for the other two systems.

At the W/A and W/O interphases, mixed monolayers were studied, consisting of a polymer with ionizable polar groups and a nearly "horizontal" disposition, poly-2-vinylpyridine (PVP), and non-ionic polymers with side chains with a "vertical" disposition with respect to the interphases, polyvinylstearate (PVS) and polyoctadecylmethacrylate (POMA), at 15, 25 and 35 ~ For the two two-component systems, PVS-PVP and POMA-PVP, complete surface compatibility at the W/A and W/O interphases was shown. A comparison of change in area as a function of mole ratios and of the thermodynamic functions of mixing at the two interphases shows that compatibility depends primarily on attractive interactions between the polar groups of the components.