Depinning of semiflexible polymers

We present a theoretical analysis of a simple model of the depinning of an anchored semiflexible polymer from a fixed planar substrate in 1+1 dimensions. We consider a polymer with a discrete sequence of pinning sites along its contour. Using the scaling properties of the conformational distribution function in the stiff limit and applying the necklace model of phase transitions in quasi-one-dimensional systems, we obtain a melting criterion in terms of the persistence length, the spacing between pinning sites, a microscopic effective length that characterizes a bond, and the bond energy. The limitations of this and other similar approaches are discussed. We also consider the general problem of thermal depinning in 1+d dimensions. In the case of force-induced unbinding, it is shown that the bending rigidity favors the unbinding through a "lever-arm effect."