Abstract
Properties of polyvinyl alcohol (PVA) at the paraffin-water interface were studied with the aid of three different monolayer techniques: (a) spreading on a constant small area (b) spreading on a large area, followed by compression and expansion cycles and (c) compressing and expanding adsorbed monolayers. Attention was paid to the influence of the percentage of acetate residues in the molecule and to the influence of the molecular weight. Spread PVA monolayers are relatively expanded. The singularity with PVAsamples containing 2% acetate groups as previously detected in measurements of the interfacial tension as a function of time and of polymer concentration, was encountered again in the π- A curves. For low molecular-weight polymers the spread monolayers exhibit hysteresis, but for high molecular-weight polymers they are completely reversible. Marked differences were observed between adsorbed monolayers of polymers of different acetate content. In PVA samples with 2% acetate groups there were clear indications of structure formation; the resulting films showed considerable hysteresis upon aging. The time effects observed with samples of PVA containing 12% acetate groups could largely be ascribed to reconformation effects, encountered before in the interfacial tension studies.
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