Diffusion and exchange of adsorbed polymers studied by Monte Carlo simulations

Monte Carlo simulations are performed of adsorbed polymers with various polymer lengths N and adsorption energies chi(s). Exchange times and the rates of lateral diffusion (along the surface) are investigated as a function of N and chi(s). Lateral diffusion is found to be a combination of reptation (diffusion of stored length along the chain) which is hardly affected by chi(s) and dominates for longer polymers, and Rouse-like behavior (sideways movement), which is strongly affected by chi(s) and dominates for shorter polymers. We relate the characteristic time for exchange of adsorbed polymers, as a function of polymer length N and adsorption energy chi(s), to the bulk diffusion coefficient at the surface density, to the polymer length and to the ratio of the surface and bulk densities. The differences of 2 and 3 orders in magnitude of the exchange times at fixed chi(s) and N, respectively, can thus be reduced to factors of 4 and 2.