Compression of polystyrene–poly(ethylene oxide) surface aggregates at the air/water interface

Abstract

We have investigated the effect of surface compression on the form of surface aggregates of diblock copolymers of polystyrene and poly(ethylene oxide) formed on a water subphase. The hexagonal order found in the surface aggregates at low surface pressures is disrupted as the surface pressure increases up to the transition in the surface pressure–area isotherm. We show that the PEO block does not go into the aqueous subphase to form a brush. Three models describing the conformation of the copolymer in the surface aggregates are proposed and their relative merits in terms of the experimental evidence are discussed. The most favored model is one where the polystyrene core of the surface aggregates sits on top of a coherent film of PEO. There is a good correlation between the behavior of the diblock copolymer and previous work by Shuler and Zisma on spread films of homopoly(ethylene oxide). In this description the PEO undergoes a dehydration process and a conformational change upon compression.