Self-consistent field study of copolymer adsorption at planar chemically 'rough' surfaces: an interplay between the substrate chemical pattern and copolymer sequence distribution

We extend the one-dimensional self-consistent field (SCF) scheme of Scheutj ens-Fleer to three dimensions (3D) and use this three-dimensional SCF model to investigate the adsorption of A-B copolymers from A homopolymer matrice s onto planar substrates composed of two chemically distinct sites (C and D ), one of which has a preferential affinity for the B segments of the copol ymer. To address the role of the substrate chemical heterogeneity on copoly mer adsorption, we keep the fraction of the C and D sites constant (50% of each site) and vary their spatial distribution on the substrate. The interp lay between the surface chemical heterogeneity and the chain microstructure is examined for A-B diblock, A-B-A, B-A-B triblock, and A-alt-B alternatin g copolymers. Our results indicate that regardless of the type of the surfa ce chemical heterogeneity, the A-B diblock and triblock copolymers adopt 'b rush'-like and 'bridge'-like structures, respectively, with the B block bei ng anchored to the substrate. In contrast, the A-alt-B macromolecule is fou nd to be 'zipped' to the substrate. For a fixed chemical potential of the c opolymer in the A-B/A mixture and the surface adsorption energy of B, the a mount of the adsorbed copolymer depends on: (1) the number of the B segment s; (2) the copolymer microstructure; and (3) the distribution of the C and D regions on the substrate. Three-dimensional maps of the spatial density o f copolymer segments provide insight into copolymer conformation at the mix ture/substrate interface and also the ability of the copolymer to recognize and mimic the substrate pattern. In addition, we discuss the circumstances under which the substrate pattern is transferred deep inside the A-B/A mix ture and those, which lead to strong damping of the substrate motif as one moves away from the substrate/mixture interface. (C) 2001 Elsevier Science B.V. All rights reserved.