Adsorption and pinning of multiblock copolymers on chemically heterogeneous patterned surfaces

The results of Monte Carlo simulations carried out on a system of multiblock copolymers having two different types of monomer units adsorbed on checker board surface configurations are presented here. We investigated the adsorption behavior for a series of different chess board square dimensions and also for various block lengths of the copolymer. We find that the specific heat capacity curves for adsorption indicate double peaks showing a two stage pattern recognition of the copolymer on the surface. It is also seen that the transition that happens at lower temperature corresponds to pinning where the junction point of the different blocks gets pinned to the interface between the different surface sites. It is interesting to see that the multiblock copolymers form multiple pinning sites on the boundary between different kinds of surface sites. There exists an intermediate size of the square on the board where the recognition and pinning are most favored and for smaller and larger size of the board and block length, the adsorption proceeds like in homopolymer on homogeneous surfaces. Unlike in the case of the simplest model of diblock copolymer on stripe-patterned surfaces [K. Sumithra and E. Straube, J. Chem. Phys. 125, 154701 (2006)], here the recognition is stronger and the average adsorption energy and the perpendicular component of the radius of gyration show distinct changes corresponding to the two transitions. The conformational properties of the multiblock copolymer near the checkered surface show interesting effects with the perpendicular component showing strong deviations from the standard behavior.