A self consistent field approach to surfaces of compressible polymer blends

TL;DR

This paper develops a self-consistent field theory incorporating classical density functional theory to study surface behaviors of compressible polymer blends, accurately predicting surface segregation phenomena.

Contribution

It introduces a novel self-consistent field approach that accounts for finite-range monomer interactions and spatially varying Flory-Huggins parameters in polymer surface studies.

Findings

Surface segregation of minority polymers is predicted accurately.

The model agrees quantitatively with Monte Carlo simulation data.

Finite-range interactions are essential for correct surface behavior modeling.

Abstract

A self consistent field theory for compressible polymer mixtures is developed by introducing elements of classical density functional theory into the framework of the Helfand theory. It is then applied to study free surfaces of binary (A,B) polymer blends. Density profiles in the one- and two-phase region are calculated as well as chain end distributions and chain orientations of the minority and the majority component. In the ideally symmetric mixture, in which the individual properties of polymers A and B are the same and both have the same surface energy, polymers of the minority component segregate to the surface, where they are exposed to less polymers of the majority component. This effect can only be captured correctly, if one accounts for the fact that the monomer-monomer interaction has finite range. As a consequence, the Flory-Huggins-parameter varies in space and depends on the concentration profiles and their derivatives. The surface segregation calculated with such an ansatz, without any fit parameter, is in reasonable quantitative agreement with data from recent Monte Carlo simulations.