INTERFACIAL PROPERTIES OF MODEL GRAFT-COPOLYMERS

Abstract

We combine measurements using a surface balance technique, ellipsometry, and surface light scattering in order to study the interfacial properties of graft copolymers and the corresponding ungrafted ''parent'' homopolymer at the air/water interface. Furthermore, by using Langmuir-Blodgett (L-B) techniques to transfer monolayers of the graft copolymers onto silica substrates, we also examine thin films at the air/solid interface by atomic force microscopy (AFM). The polymers are composed of a poly(ethyl acrylate) (PEA) main chain and pendant polystyrene (PS)grafts. In addition, the copolymers have on average one, three, and five PS grafts per PEA chain backbone. The PEA component in these graft copolymers provide sufficient hydrophilicity to form stable monolayers. Our results show that, at low surface concentration, the surface pressure of these copolymers is influenced mainly by the PEA backbone. At high surface concentration, the surface pressure deviates from that found for the PEA homopolymer and depends on the number of PS grafts. This phenomenon is due primarily to the overlap of the grafted PS chains. The interfacial structure of these graft copolymers can be derived from the results of the surface pressure isotherm and ellipsometry measurements and are further confirmed by the results of the surface light scattering and AFM measurements.