Adsorption-active polydisperse brush with tunable molecular mass distribution

TL;DR

This study investigates how polydisperse polymer brushes with adsorption-active chains respond to surface affinity changes, revealing preferential adsorption of shorter chains and the ability to tune molecular mass distribution.

Contribution

It introduces a theoretical and numerical analysis of adsorption-active polydisperse brushes, showing how surface interactions can selectively alter chain distributions.

Findings

Shorter chains are preferentially adsorbed.

Surface affinity changes can transform the molecular mass distribution.

The outer brush can become nearly monodisperse.

Abstract

Recently a novel class of responsive uncharged polymer brushes has been proposed [Klushin et al, J. Chem. Phys. 154, 074904 (2021)] where the brush-forming chains have an affinity to the substrate. For sufficiently strong surface interactions, a fraction of chains condenses into a near-surface layer, while the remaining ones form the outer brush with a reduced grafting density. The dense layer and the more tenuous outer brush can be seen as coexisting microphases. The effective grafting density of the outer brush is controlled by the adsorption strength and can be changed reversibly as a response to changes in environmental parameters. In this paper we use numerical self-consistent field calculations and theoretical considerations to study this phenomenon in polydisperse brushes. Our results reveal an unexpected effect: Although all chains are chemically identical, shorter chains are adsorbed preferentially. Hence, with the increase in the surface affinity parameter, a reduction in the surface grafting density of the residual brush is accompanied by a change in the shape of its molecular mass distribution. In particular, an originally bidisperse brush can be effectively transformed into a nearly monodisperse one containing only the longer chain fraction.