ADSORPTION OF MULTIBLOCK COPOLYMERS AT INTERFACES BETWEEN SELECTIVE SOLVENTS - SINGLE-CHAIN PROPERTIES

We consider the configuration properties of a periodic multiblock copo lymer made of a regular alternating succession of two monomer species A and B near interfaces between two weakly selective solvents alpha an d beta. Both solvents are assumed to be good, but their quality is sli ghtly different for both monomer species: Solvent alpha is better for A than for B, and vice versa. We map the problem into a corresponding homopolymer adsorption problem by considering the individual AB-dibloc k units as effective segments of a coarse-grained chain. The renormali zed segments have an effective interaction with the solvent-solvent in terface. This is calculated to second order in a perturbation expansio n. We show that attraction of a single diblock by the interface is a s econd-order effect. In the symmetric case the first-order contribution vanishes and the interface is always attractive. The strength of the effective attraction scales as (chi n)(2), where chi is the selectivit y strength and n the length of an AB unit. When the interface potentia l is not symmetric with respect to the block species, a first-order re pulsive contribution appears. As a result we predict a discontinuous d esorption transition for that case, controlled by the asymmetry. In ma rked difference to the usual adsorption problem, the largest stable ad sorption blob is of finite size.