Adsorption characteristics of water‐soluble polymers at aqueous‐organic liquid interfaces

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Abstract
Adsorption characteristics of water‐soluble polymers, as denoted by interfacial tension measurements, were investigated at aqueous‐organic liquid interfaces via the volume ‐drop and pendant‐drop techniques. Interfacial results obtained from both studies parallel the alkanol adsorption data of Bartell and Davis. If surface tension data are included in the comparison, discrepancies with respect to the alkanol data are observed; macromolecular aqueous solution surface pressures are substantially lower than corresponding interfacial pressures at aqueous‐hexane boundaries. Minute amounts of organic impurities in the air phase effect surface pressures approximate with aqueous‐hexane boundary data. The observations reflect a lesser degree of unfolding and surface occupation at the aqueous‐air interface than at high energy aqueous‐organic boundaries.Poly(ethylene oxide) possesses a random conformation in bulk benzene solutions and a highly ordered structure in aqueous solutions. An inquiry into boundary conformational effects was undertaken via pendant‐drop studies of PEO adsorption at the common interface from both benzene and aqueous phases. Despite different conformations in two media with different solvating characteristics equivalent interfacial pressures were obtained. Interfacial pressure equilibrium attainment was achieved more rapidly from the aqueous phase. Additional hexane‐water and aqueous‐air boundary studies show the faster equilibrium attainment rate to be related more to the ability of the benzene phase to rapidly orient interfacial polymer segments than to conformational effects.