Issue 12, 2013

On the collapse transition of a polymer brush: the case of lateral mobility

Abstract

We consider a polymer brush composed of end-grafted polymer chains. Classical theory advocates that a worsening of the solvent quality results in a smooth decrease of the brush height from a swollen to a dense brush. We report that a homogeneous brush under poor solvent conditions can have a negative surface pressure, indicating an instability in favour of lateral segregation. Also by using a two-gradient version of the self-consistent field (SCF) theory we show that, in contradiction to the classical result, but in line with the negative pressure, the collapse transition for laterally mobile chains has a first-order character, exemplified by the presence of a compact brush that coexists with a dilute gas of end-grafted chains. The dense brush assumes a pancake shape wherein the chains balance the stretching entropy against surface energies. The height of the pancake scales sub-linearly with the chain length because the local grafting density decreases with increasing chain length. In analogy with wetting studies we discuss how the spreading parameter has an influence on the pancake structure. Accordingly, the height increases with worsening of the solvent quality and decreases with increased affinity for the substrate. The two-phase state is expected in many practical situations.

Graphical abstract: On the collapse transition of a polymer brush: the case of lateral mobility

Article information

Article type
Paper
Submitted
09 Nov 2012
Accepted
16 Jan 2013
First published
11 Feb 2013
This article is Open Access
Creative Commons BY license

Soft Matter, 2013,9, 3341-3348

On the collapse transition of a polymer brush: the case of lateral mobility

F. A. M. Leermakers and S. A. Egorov, Soft Matter, 2013, 9, 3341 DOI: 10.1039/C3SM27586H

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