Adsorption of multiblock copolymers at interfaces between selective solvents: Single-chain properties

We consider the configuration properties of a periodic multiblock copolymer made of a regular alternating succession of two monomer species A and B near interfaces betwen two weakly selective solvents α and β. Both solvents are assumed to be good, but their quality is slightly different for both monomer species: Solvent α 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-diblock units as effective segments of a coarse grained chain. The renormalized segments have an effective interaction with the solvent-solvent interface. This is calculated to second order in a perturbation expansion. We show that attraction of a single diblock by the interface is a second order effect. In the symmetric cse the first order contribution vanishes and the interface is always attractive. The strength of the effective attraction scales as (χn${)}^2$, where χ is the selectivity strength and n the length of an AB unit. When the interface potential is not symmetric with respect to the block species, a first order repulsive contribution appears. As a result we predict a discontinuous desorption transition for that case, controlled by the asymmetry. In marked difference to the usual adsorption problem, the largest stable adsorption blob is of finite size. © 1996 The American Physical Society.