Arrested spinodal decomposition in polymer brush collapsing in poor solvent

TL;DR

This study investigates the collapse dynamics of densely grafted polymer brushes in poor solvents, revealing an arrested spinodal-like inhomogeneous structure that remains stable due to grafting constraints.

Contribution

It demonstrates that polymer brush collapse leads to a stable, inhomogeneous structure resembling spinodal decomposition, differing from individual chain behavior and showing no coarsening.

Findings

Collapsed brush forms inhomogeneous density patterns

Structure resembles spinodal decomposition with characteristic length scale

No coarsening occurs, structure remains stable

Abstract

We study the Brownian dynamics of flexible and semiflexible polymer chains densely grafted on a flat substrate, upon rapid quenching of the system when the quality of solvent becomes poor and chains attempt collapse into a globular state. The collapse process of such a polymer brush differs from individual chains, both in its kinetics and its structural morphology. We find that the resulting collapsed brush does not form a homogeneous dense layer, in spite of all chain monomers equally attracting each other via a model Lennard-Jones potential. Instead, a very distinct inhomogeneous density distribution in the plane forms, with a characteristic length scale dependent on the quenching depth (or equivalently, the strength of monomer attraction) and the geometric parameters of the brush. This structure is identical to the spinodal-decomposition structure, however, due to the grafting constraint we find no subsequent coarsening: the established random bundling with characteristic periodicity remains as the apparently equilibrium structure. We compare this finding with a recent field-theoretical model of bundling in a semiflexible polymer brush.