The behavior of linear polymers at interfaces

Abstract

Monolayers of synthetic linear polymers were studied by means of measurements of interfacial pressure and potential at air/water and oil/water interfaces. The polymers examined were: poly- N-vinyl pyrrolidone, polyvinyl acetate, polyvinyl stearate, polymethyl methacrylate, polymethacrylic acid, copolymers of polymethacrylic acid and diethylaminoethyl vinyl ether, poly-ϵ-caproamide, polyethylene terephthalate, and polyacrylonitrile. All the polymers except polyvinyl acetate give films of the condensed type at the air/water interface, whereas all the polymers except polyethylene terephthalate and polyacrylonitrile give films of the expanded type at the oil/water interface. The film of the condensed type gives a constant surface moment up to a collapse point, and the true molecular weight can be obtained from the surface pressure. The film of the expanded type gives a constant surface moment at larger areas, but the moment changes at a certain area. In this case, a smaller molecular weight than the true one is obtained from the surface pressure. The film of the expanded type at the oil/water interface has segments in the main chain as a statistical kinetic unit, each consisting of about 48 skeletal atoms, and is discussed in the light of the Singer equation of state. The value of surface moment is determined chiefly by the orientation of the CO bond. The behavior of an ampholyte was studied by the measurement of interfacial potential. The results showed that the amine groups could not be ionized more than about 20 mole per cent owing to the strong cohesion between major nonionized carboxyl groups at the air/water interface, but such a restriction was not found at the oil/water interface owing to the sufficiently expanded state. The extension of these conclusions to proteins is suggested.