TETHERED ADSORBING CHAINS - NEUTRON REFLECTIVITY AND SURFACE PRESSUREOF SPREAD DIBLOCK COPOLYMER MONOLAYERS

Spread monolayers of diblock copolymers of styrene and ethylene oxide at the air-water interface were studied by surface pressure measuremen ts and neutron reflectivity, as a function of coverage sigma and chain length N. The surface pressure data have three regions, one at low co verage, where a relatively sharp increase due to increasing intermolec ular interaction is found, a more gently increasing part at intermedia te coverage, where the poly(ethylene oxide) block gradually desorbs to form a blush, and a sharply increasing part at high coverage, where t he blush is compressed. The neutron reflectivity measurements, taken i n the intermediate and high coverage regions, confirm the presence of a brush with a thickness scaling, by approximation as sigma(1/3). Thes e brushes could be compressed by a factor of about 5 without desorptio n occurring. The observations are in good agreement with numerical cal culations based on a mean field lattice model for terminally anchored, adsorbing chains. These calculations predict a gradual change in the average configuration from a flat, adsorbed state to a brush consistin g of stretched chains.