Surface segregation of conformationally asymmetric polymer blends

TL;DR

This paper extends Edwards' method to study surface segregation in conformationally asymmetric polymer blends, deriving analytical expressions for polymer concentration profiles near a surface.

Contribution

It introduces a generalized approach to analyze surface effects in asymmetric polymer blends using effective potentials, providing new analytical insights.

Findings

Stiffer polymers tend to enrich at the surface depending on segment length differences.

Shorter polymers preferentially adsorb at the wall in blends with different degrees of polymerization.

Analytical expressions relate surface concentration excess to polymer conformational asymmetry.

Abstract

We have generalized the Edwards' method of collective description of dense polymer systems in terms of effective potentials to polymer blends in the presence of a surface. With this method we have studied conformationally asymmetric athermic polymer blends in the presence of a hard wall to the first order in effective potentials. For polymers with the same gyration radius $R_g$ but different statistical segment lengths $l_{A}$ and $l_{B}$ the excess concentration of stiffer polymers at the surface is derived as $% \delta \rho _{A}(z=0)\sim (l_{B}^{-2}-l_{A}^{-2}){\ln (}R_{g}^{2}/l_{c}^{2}{)%}$, where $l_{c}$ is a local length below of which the incompressibility of the polymer blend is violated. For polymer blends differing only in degrees of polymerization the shorter polymer enriches the wall.