Lateral compression of homopolymers and copolymers at the air-liquid interfaces for good solvents

Abstract

End-tethered polymer layers are formed when a collection of polymers is anchored by one end to a surface, with the reminder dangling into solvent. These systems have been studied extensively both experimentally and theoretically, and numerical self- consistent field (nSCF) theory can now explain much of their structure and physical behavior very well. However, the surface pressure is not yet understood. -- Bijsterbosch et al. performed experiments in which they examined a series of polystyrene-poly(ethylene ) (PS-PEO) diblock copolymers at the air-water interface with varying length of PEO block. They found that surface pressure excess varies smoothly and slowly with polymer density. On the other hand, Kent et al. investigated systems of diblock copolymer poly(dimethylsiloxane-styrene) (PDMS-PS) spread as a monolayer at the free surface of ethyle benzoate (EB). In these systems PDMS lies flat on the top of EB, with PS dangling into EB which is a good solvent for PS. They reported that surface pressure excess varies smoothly and slowly at low density, then quickly at high density. -- All theoretical treatments except one give weak variation similar to observations of Bijsterbosch and coworkers. The exception is the nSCF calculation of Baranowski. In this thesis, nSCF calculations have been performed to examine Baranowski's work, and to model Kent's experiments. The results are in good agreement with predictions of the scaling theories for the surface pressure isotherms, which are also compatible with experimental measurements performed by Bijsterbosch et al.