The adsorption and partitioning of self-avoiding walk polymer chains into pores from a bulk theta solution

Abstract

Monte Carlo simulations of self-avoiding walk (SAW) polymer chains on a simple cubic lattice were used to study the adsorption and partitioning of the chains into pores from a bulk Θ solution. The behavior of the SAW chains confined in pores at the bulk Θ temperature was found to differ from that of the Gaussian chains. When confined in a slit or in a square channel, the radius of gyration of a Θ chain perpendicular to the direction of the confinement was shown to increase in comparison with the radius of gyration in bulk solution. The solvent quality in the pore was shown to be better than the Θ solvent, causing the expansion of the chain in the pore. When terminally anchored onto a solid surface, the reduced polymer-surface interaction at the critical adsorption point, εwca, was found to be −0.252±0.001, which differs from the value of εwca for chains without excluded volume effects, a category including random walks and non-reversing random walks on the lattice. When partitioning into a pore modeled as a slit, the polymer-surface interaction at the critical point was shown to be the same as the critical adsorption point and does not shift with the slit width. But when partitioning into a pore modeled as a square channel, the polymer–surface interaction at the critical point was shown to shift with the width of the square channel. At the critical condition point, the partition coefficient of the SAW Θ chains was greater than one in both types of pores. These results differ from the results of the Gaussian chains; instead, they are similar to that of SAW chains in athermal solvent.