Diffusive Spreading of Chainlike Molecules on Surfaces

TL;DR

This paper investigates the diffusion behavior of chainlike molecules on surfaces, revealing unusual coverage-dependent diffusion coefficients and developing an analytic model that aligns with simulation results.

Contribution

It introduces a fluctuating bond model to analyze diffusion coefficients and explains the coverage dependence with an analytic approach.

Findings

D_c(theta) increases then decreases to zero as coverage approaches one

Entropic repulsion causes steep density profiles in spreading droplets

Analytic model matches simulation data for D_c(theta)

Abstract

We study the diffusion and submonolayer spreading of chainlike molecules on surfaces. Using the fluctuating bond model we extract the collective and tracer diffusion coefficients D_c and D_t with a variety of methods. We show that D_c(theta) has unusual behavior as a function of the coverage theta. It first increases but after a maximum goes to zero as theta go to one. We show that the increase is due to entropic repulsion that leads to steep density profiles for spreading droplets seen in experiments. We also develop an analytic model for D_c(theta) which agrees well with the simulations.