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

We have investigated the effect of surface compression on the form of surfa ce aggregates of diblock copolymers of polystyrene and poly(ethylene oxide) formed on a water subphase. The hexagonal order found in the surface aggre gates at low surface pressures is disrupted as the surface pressure increas es 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 aggrega tes are proposed and their relative merits in terms of the experimental evi dence are discussed. The most favored model is one where the polystyrene co re of the surface aggregates sits on top of a coherent Dlm of PEO. There is a good correlation between the behavior of the diblock copolymer and previ ous work by Shuler and Zisman(1) on spread films of homopoly(ethylene oxide ). In this description the PEO undergoes a dehydration process and a confor mational change upon compression.