Formation of polymer brushes

TL;DR

This paper models the extraction and association processes of stickers in polymer systems, revealing that tension fluctuations enable barrier crossing and that these processes are local and independent of molecular weight.

Contribution

It introduces a statistical physics description of sticker dynamics in stretched polymer brushes, emphasizing tension fluctuations as the key mechanism.

Findings

Barriers are crossed by tension fluctuations.

Processes are local with friction independent of molecular weight.

High potential barriers hinder equilibrium structure development.

Abstract

In systems such as block copolymer mesophases or physical gels formed by associating copolymers, the dynamical properties are often controlled by the extraction/association of a sticking group. We propose a description of the extraction/association process of a single sticker. The statistical physics of these associated systems is usually dominated by stretched brush-like regions. A sticker has to overcome a potential barrier both to penetrate the stretched structure or to escape a favorable region built by associated stickers. Our main result is that these barriers are crossed by tension fluctuations and that the corresponding processes are thus local with a friction independent of molecular weight. When the potential barriers are high, the (very stretched) equilibrium structures are not likely to develop on reasonable time scales. Stretched model systems may also be grown in situ from nuclei bearing initiating groups. These, irreversibly bound structures, are also briefly discussed.