Copolymer adsorption on planar substrates with a random distribution of chemical heterogeneities

We use a 3D SCF model of polymer adsorption to investigate the adsorption o f A-B copolymers from A-B/homopolymer A mixtures onto planar substrates com posed of two chemically distinct randomly distributed sites, one of which h as a preferential affinity for the B segments of the copolymer. Our results show that when the chemically heterogeneous substrate motifs are recognize d by the copolymer, the copolymers can transcript them with a relatively hi gh fidelity into three dimensions. The way the surface motif is transferred is strongly dictated by the copolymer sequence. We show that block copolym ers are capable of detecting small clusters of the substrate adsorption sit es. The fidelity of the pattern shape and the distance from the substrate t o which the pattern gets transferred increases with decreasing the length o f the adsorbing block of the copolymer. Our results also indicate that incr easing (i) the interactions between the copolymer adsorbing segments and th e "sticky" points at the substrate, and/or (ii) the repulsion between the c opolymer segments increases the total adsorbed amount of the copolymer at t he mixture/substrate interface but it decreases the fidelity of the substra te chemical pattern transfer into the mixture. We show that, in contrast to the block copolymers, macromolecules with alternating sequence distributio ns adopt different conformations on random substrates in that they tend to localize at the boundaries between the C/D surface sites, where the substra te chemical pattern more closely matches the sequence distribution of the B stickers along the copolymer. We claim that this feature allows us to use alternating copolymers in situations where one needs to suppress the chemic al pattern transfer on such random substrates. (C) 2001 American Institute of Physics.