Exclusion Zone of Convex Brushes in the Strong-Stretching Limit

TL;DR

This paper analyzes the exclusion zone of convex polymer brushes under strong stretching, extending existing models to account for curvature effects and providing exact and numerical solutions for the exclusion zone size.

Contribution

It extends the self-consistent model to determine the exclusion zone in convex brushes, including exact solutions for weak curvature and numerical analysis for stronger curvature.

Findings

Exclusion zone size decreases from melt to solvent conditions.

Relative differences in exclusion zone size grow exponentially as curvature approaches zero.

The model provides a new integral equation framework for convex brush analysis.

Abstract

We investigate asymptotic properties of long polymers grafted to convex cylindrical and spherical surfaces, and, in particular, distribution of chain free ends. The parabolic potential profile, predicted for flat and concave brushes, fails in convex brushes, and chain free ends span only a finite fraction of the brush thickness. In this paper, we extend the self-consistent model developed by Ball, Marko, Milner and Witten to determine the size of the exclusion zone, i.e. size of the region of the brush free from chain ends. We show that in the limit of strong stretching, the brush can be described by an alternative system of integral equations. This system can be solved exactly in the limit of weakly curved brushes, and numerically for the intermediate to strong curvatures. We find that going from melt state to theta solvent and then to marginal solvent decreases relative size of the exclusion zone. These relative differences grow exponentially as the curvature decreases to zero.