Adsorption of Homopolymers on a Solid Surface: A Comparison between Monte Carlo Simulation and the Scheutjens‒Fleer Mean-Field Lattice Theory

Abstract

A comparison of a multichain Monte Carlo simulation of homopolymer adsorption on a solid surface with the mean-field lattice theory of Scheutjens‒Fleer is presented. The comparison reveals certain systematic deviations between the theory and the simulation, which are reflected in the bound fraction of the chain, surface coverage, and the adsorbed amount. Such deviations can be attributed to two approximations adopted in the theory. One approximation is the allowance of direct back-fold of the chain, and the other approximation is the random-mixing within each layer. The allowance of direct back-fold of the chain is a result of treating the chain as a Markovian chain. It gives rise to a difference in the number of allowed conformations compared to the Monte Carlo simulation. However such differences do not affect the distribution of chain segments in homogeneous solution. It would only cause a difference when the chain is in an inhomogeneous solution or when it encounters an impenetrable solid surface. The study reveals that the deviation in bound fraction introduced due to the allowance of direct chain back-fold persists throughout the whole range of concentration. It is more pronounced at weak adsorption. On the other hand, the random mixing approximation works better in moderate concentration under weak adsorption since the adsorbed chains can more easily penetrate each other. In the strong adsorption limit, the adsorbed chains are confined to two dimensions and they resist interpenetration. Thus the deviation in surface coverage and adsorbed amount caused by the random mixing between the theory and simulation is more pronounced under strong adsorption. © 1994, American Chemical Society. All rights reserved.

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Langmuir

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