Adsorbed polymers on an inhomogeneous surface: pulling at an angle

We consider a partially directed walk model in three dimensions to study the problem of a homopolymer adsorbing on an inhomogeneous surface while subject to a force applied at the terminal monomer. The force has components in the surface parallel and perpendicular to the direction of the inhomogeneity as well as a component perpendicular to the surface. Depending on the relative values of these components, the force can either enhance the adsorption transition or lead to desorption of an adsorbed polymer. We solve the problem exactly and also discuss a simple approximate treatment of this problem, applicable at low temperatures. The approximation is exact at zero temperature and models the exact results extremely well for low temperatures. In addition, the treatment leads to an improved physical understanding of the shapes of the force-temperature curves at low temperatures.