Parameters influencing diffusion dynamics of an adsorbed polymer chain

Brownian dynamics simulations with hydrodynamic interaction (HI) are performed to study the effect of chain length on the diffusion of a polymer chain adsorbed onto flat surfaces. Bead-rod as well as bead-spring chains, with Hookean and finitely extensible nonlinear elastic (FENE) springs, are used to model the polymer chain, and the no-slip boundary condition for the solvent is incorporated exactly. Simulations for short chains (N≤100) predict that the translational diffusivity in the planar direction D ∼ N-ν, where N is the chain length, with ν 0.75 for bead-rod chains and bead-spring chains connected by stiff FENE springs and ν 1 for bead-spring chains connected by flexible FENE and Hookean springs. We find that near chemically homogeneous surfaces, the scaling exponent ν depends upon three factors: chain flexibility, strength of HI, and solvent quality. The ν value changes from 0.75 to 1 with either an increase in chain flexibility, a decrease in the strength of HI, or a decrease in solvent quality. However, near a chemically heterogeneous surface, ν is always 1.