Solvent response of diblock copolymer brushes

Abstract

We have performed continuum self-consistent field (SCF) calculations to study the solvent response of diblock copolymer A-B brushes, where all copolymer chains are grafted onto a flat and impenetrable substrate and immersed in a solvent. In order to avoid the numerical problem associated with the delta-function initial condition specifying that all A-ends are grafted at a small distance from the impenetrable substrate, we numerically integrate the Chapman-Kolmogorov equations, rather than solving the modified diffusion equations, when chains are strongly stretched (e.g., at a high grafting density or in a good solvent). This gives much better numerical performance of SCF calculations in such cases. The solvent response of the diblock copolymer brushes is characterized by the changes in brush height and surface-layer composition (i.e., relative fraction of A segments in the copolymers present in the region above the brush height) in three different solvents: Neutral, A-like, and B-like. We have systematically studied the influence of copolymer composition, copolymer chain length, chain-grafting density, and A-B incompatibility on the solvent response of diblock copolymer brushes. Our results are in good agreement with available experiments and can provide some guidance to the design of smart surfaces from diblock copolymer brushes best suited for targeted applications.