Structure of Poly(ethylene oxide) Surfactant Polymers at Air−Water and Solid−Water Interfaces

Abstract

The surface active properties of novel poly(ethylene oxide) (PEO) containing surfactant polymers were investigated at the air−water and graphite−water interfaces. The surfactant polymers are comblike polymers consisting of a poly(vinylamine) backbone with 2 kDa PEO and hexanal side chains. The polymers were prepared with various grafting ratios of the two side chains. Surface pressure isotherms were obtained for spread monolayers for the range of polymer compositions. Two transitions are observed at 5 and 11 mN/m, which are interpreted as stages of desorption for the PEO side chains from the interface into the aqueous subphase. It is demonstrated that it is possible to scale the isotherms quantitatively to provide an accurate determination of the side chain composition. We characterized the adsorption process of two of the surfactant polymers at the water−graphite interface, using tapping mode atomic force microscopy (AFM). With high hexanal:PEO content (e.g., 8:1), the surfactant polymer rapidly forms a compact and complete monolayer 1.2 nm thick. At lower hexanal:PEO content (e.g., 4:1), a disordered layer is formed. After several hours, this layer rearranges into small scattered domains with banded structures. The structure of these layers is interpreted using a model of surface adsorption and the surface pressure isotherms.