END-GRAFTED POLYSTYRENE BRUSHES IN A CRITICAL BINARY MIXTURES. K. Satija, P.D. Gallagher, A. Karim, NIST, Gaithersburg, MD and L. Fetters, Exxon Corporate Research Laboratories, Annandale, NJ

We report neutron reflectivity measurement on end-grafted polystyrene brushes in contact with binary mixtures of cyclohexane and methanol. End-grafting was done by adsorbing trichlorosilane terminated perdeuterated polystyrene on silicon substrates. Neutron reflectivity measurements were done with mixtures of cyclohexane and methanol of various proportions (including the critical composition) and at different temperature. On the methanol rich side the brush is quite collapsed, however, the brush height increases on decreasing the temperature indicating that the proportion of cyclohexane next to the brush increases upon lowering the temperature. As we lower thetemperature through the phase transition, the brush streches suddenly andfurther decrease of temperature brings about a normal decrease in brushheight. On the cyclohexane rich side, a small amount of addition ofmethanol (5%) gives rise to a very large change in the reflectivity. Our preliminary results in this regime indicate that with the additionof methanol the brush has streched considerably compared to the pure cyclohexane case. Results of all these composition and temperaturescans will be described.