Compressible or incompressible blend of interacting monodisperse star and linear polymers near a surface

TL;DR

This study models a mixture of star and linear polymers near a surface, revealing how surface interactions influence monomer density profiles and polymer enrichment, with a focus on the effects of star arm number and compressibility.

Contribution

It introduces a fast, efficient lattice model method to analyze polymer-surface interactions, including compressible and incompressible blends, extending previous linear-polymer studies.

Findings

Linear polymers are enriched near the surface due to entropic effects.

Star monomers can be overall enriched depending on surface interactions.

Critical star arm number affects surface enrichment, increasing with compressibility.

Abstract

We consider a lattice model of a mixture of repulsive, attractive, or neutral monodisperse star (species A) and linear (species B) polymers with a third monomeric species C, which may represent free volume. The mixture is next to a hard, infinite plate whose interactions with A and C can be attractive, repulsive, or neutral. These two interactions are the only parameters necessary to specify the effect of the surface on all three components. We numerically study monomer density profiles using the method of Gujrati and Chhajer that has already been previously applied to study polydisperse and monodisperse linear-linear blends next to surfaces. The resulting density profiles always show an enrichment of linear polymers in the immediate vicinity of the surface, due to entropic repulsion of the star core. However, the integrated surface excess of star monomers is sometimes positive, indicating an overall enrichment of stars. This excess increases with the number of star arms only up to a certain critical number and decreases thereafter. The critical arm number increases with compressibility (bulk concentration of C). The method of Gujrati and Chhajer is computationally ultrafast and can be carried out on a PC, even in the incompressible case, when simulations are unfeasible. Calculations of density profiles usually take less than 20 minutes on PCs.