Monte Carlo study of block copolymer adsorption from dilute solutions

We present results from Monte Carlo simulations of a lattice model for block copolymers in dilute solution; we emphasize adsorption on a substrate. The model includes pairwise short-ranged interactions between monomers as well as interactions between monomers and the substrate. By varying the relative values of different interactions, the lengths of the different blocks in the copolymer, and the temperature, we are able to study systematically a variety of thermodynamic properties, including especially the adsorption temperature and the density distributions for the various blocks in the polymer. Special attention is paid to the case in which the A monomers attract each other and are attracted to the substrate while the B monomers experience no attractive forces from either themselves, the A monomers, or the substrate. This case corresponds to having a selective solvent that is good for the B's and poor for the A's. Then the A block becomes adsorbed at sufficiently low temperatures while a block of B's does not, but rather extends some distance into the solvent. We also present for comparison simulations of the properties of a single block of monomers anchored at one end to the substrate. A general conclusion of this comparison is that when the A block of the copolymer is firmly adsorbed to the substrate, the behavior of the B block or blocks is qualitatively much the same as the behavior of a single block anchored at one end.