Diffusion of end-grafted chain-like molecules on surfaces

We have studied the diffusion of short end-grafted chain-like molecules on smooth surfaces using the fluctuating bond model and Monte Carlo simulations. In our simulations, one end of each chain is restricted to lie on the surface, where it can move in a diffusive manner. The other segments of the chains can fluctuate freely above the surface. We study the behavior of the collective diffusion coefficient, DC(θ), as a function of the coverage, θ. Through simulations, we demonstrate that with relatively short end-grafted chains, DC(θ) first increases as a function of θ but then eventually approaches zero for θ→1. This is caused by an entropy-induced repulsive interaction in analogy to the case of purely 2D diffusion of polymers.