PREFERENTIAL SOLVATION IN POLY(STYRENE) BRUSHES

We have investigated the preferential solvation effect in poly(styrene ) brushes immersed in a binary mixture. The small angle neutron scatte ring technique has been used for determining the chemical composition of the mixture trapped into the polymer interface. When both of the so lvents are good for the polymer, no effect has been noticed. However, for a mixture of acetone and cyclohexane (both poor solvents for the p oly(styrene)), we have observed that this mixture can behave as a good solvent-cosolvency effect. The thickness of the interface can be twic e that in either pure acetone or pure cyclohexane. Moreover, the chemi cal composition of the mixture trapped into the brush is different fro m that of the bulk: it is enriched in the component which tends to ach ieve the best composition (for which the thickness is maximum). Finall y, for a mixture of a good and a poor solvent, we recover the same non linear behavior as we have described previously (ref 3). This is assoc iated with a strong preferential solvation of the good solvent.