  We investigate the folding and forced-unbinding transitions of adsorbed
semiflexible polymer chains using theory and simulations. These processes
describe biologically relevant phenomena that include adhesive interactions
between proteins and tethering of receptors to cell walls. The binding
interface is modeled as a solid surface and the worm-like chain is used for the
semiflexible chain. Using Langevin simulations we examine the ordering kinetics
of racquet-like and toroidal structures in the presence of attractive
interaction between the surface and the polymer chain. For a range of
interactions, temperature, and the persistence length l_p we obtained the
monomer density distribution n(x) for all the relevant morphologies. The
simulated results for n(x) are in good agreement with theory. The formation of
toroids on the surface appears to be a first order transition. Chain-surface
interaction is probed by subjecting the surface structures to a pulling force
f. The average extension x as a function of f exhibit sigmoidal profile with
sharp all-or-none transition at the unfolding f_c which increases for more
structured states. Simulated x compare well with the theoretical predictions.
The critical force f_c is a function of l_s/l_c for a fixed temperature, where
l_c, l_s are the length scales that express the strength of the intramolecular
and chain-surface attraction, respectively. For a fixed l_s, f_c increases as
l_p decreases.
