Depletion interaction between cylindrical inclusions in polymer brushes

TL;DR

This study investigates how cylindrical inclusions in polymer brushes experience depletion attraction, revealing non-monotonic behavior influenced by brush height, with implications for colloid-polymer systems and biological cell surfaces.

Contribution

It introduces a molecular dynamics and theory-based analysis of depletion interactions in polymer brushes, highlighting the role of correlation blobs and brush height effects.

Findings

Depletion attraction is mediated by correlation blobs in the brush.

In tall brushes, entropy competition causes non-monotonic attraction behavior.

Implications for protein clustering on cell surfaces via glycocalyx interactions.

Abstract

Inclusions in mobile brushes experience apparent (depletion) attraction, which arises from a tendency to minimize the volume of depletion zones around the inclusions, thereby to maximize the entropy of the surrounding polymers. Here, we study the brush-induced depletion attraction between cylindrical inclusions using molecular dynamics simulations and the Asakura-Oosawa theory. Our considerations find that the correlation blobs defined in the brush environment serve as the fundamental units of the attraction. In tall brushes, however, the entropy of the overgrown polymer competes with the depletion attraction between the inclusions. As a result, the brush-induced depletion interaction displays non-monotonic variations with the brush height. Our study not only expands the repertoire of colloid-polymer mixtures to depletion interactions in brushes, but also suggests the brush-induced depletion interaction as a previously unappreciated mechanism for glycocalyx-induced protein cluster formation on cell surfaces.