Surface diffusion and relaxation of partially adsorbed polymers

We studied by lattice simulation the surface diffusion and relaxation of is olated, self-avoiding polymers partially adsorbed onto a flat surface. The key parameters describing the system are the number of segments in the chai n, N, the adsorption energy of a segment, expressed as a dimensionless surf ace temperature T-s, and the segmental friction factor on the surface relat ive to that in the hulk, zeta(s)/zeta(b). The simulation data indicate Rous e scaling of the surface diffusion coefficient, D-parallel to, and in-plane relaxation time, tau, versus N for all values of T-B and zeta(s)/zeta(b) s tudied. A simple application of the Rouse model to a partially adsorbed cha in, which ignores fluctuations in adsorbed trains, yields a formula for D-p arallel to with the correct N-scaling. It can account for the effects of T- s when zeta(s)/zeta(b) is finite (less than or similar to 10), but it fails when zeta(s)/zeta(b) diverges, predicting no surface diffusion at all, whe reas simulations indicate finite surface mobilities facilitated by a caterp illar-like motion. (C) 2000 John Wiley & Sons, Inc.