Compression of an adsorbed polymer layer of fixed mass: A Monte Carlo study

Lattice Monte Carlo simulations are used to analyze the normal force induce d by interacting polymer chains between an athermal plane and an adsorbing plane in an athermal (good) solvent. The simulations are carried out under conditions of "restricted equilibrium" in which the amount of polymer in th e system is not allowed to fluctuate. The results are compared with numeric al, lattice mean-field calculations. We observe that mean-field theory usua lly overestimates the magnitude of the force. A substantial improvement in the comparison is obtained when interpreted with respect to properties of t he corresponding unconfined layer at equilibrium with the bulk solution. Fo r instance, in the case of high coverage, simulations and numerical mean-fi eld theory are in good agreement at the same relative coverage, e.g., the s ame ratio of surface coverage to saturation coverage. Comparison with asymp totic scaling predictions does not yield unequivocal results for these chai n lengths, but the results are roughly consistent with the nontrivial (-3) power law. A brief analysis of the compression of two layers against each o ther shows a strong similarity with the main results of this work when the surfaces bear an excess of adsorbed polymer chains (i.e., high coverage).