Pulling polymers adsorbed on a striped surface

We consider the adsorption of a linear homopolymer on a striped surface where the monomers have different energies of interaction with each of the two kinds of stripe. In addition, the polymer is subject to a force that tends to desorb the polymer, and the force can be applied at different angles. We consider both a partially directed walk model and a self-avoiding walk model. We solve the problem for the partially directed walk problem essentially completely and give phase diagrams (in the force-temperature plane) for various values of the direction in which the force is applied. The phase diagrams show re-entrance phenomena and, for some force directions, degenerate ground states. We also present a low temperature treatment that helps to interpret the results from the combinatorial solution. For the self-avoiding walk model we present Monte Carlo results and show that the phase diagrams for the partially directed walk and self-avoiding walk are qualitatively similar and, at low temperatures, are in quantitative agreement.