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Issue 3, 2013
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A new pathway for the re-equilibration of micellar surfactant solutions

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Abstract

Micellar surfactant solutions are generally assumed to undergo restructuring via stepwise monomer loss following a dilution. This process is captured by the Becker–Döring equations, an infinite-dimensional system of ordinary differential equations for the concentration of each aggregate in solution. We reveal certain classes of surfactants, such as the non-ionic family CnEm, for which the predicted re-equilibration times via stepwise monomer loss are far greater than those observed experimentally. We investigate two alternative pathways for re-equilibration, first allowing for micelles to break down into two aggregate fragments rather than stepwise monomer release, and secondly by allowing aggregates to merge together to form large super-micelles that exceed the size of a proper micelle. While the former shows no discernible difference in the predicted time to re-equilibration, the latter provides an alternative pathway to re-equilibration: the formation of unstable super-micelles that break down to proper micelles via a cascade of stepwise monomer release. The new theory is shown to describe the re-equilibration of any surfactant system, with the conventional Becker–Döring theory forming a subset of the model that describes the behaviour of a small range of surfactant systems with high critical micelle concentrations and low aggregation numbers. The pathway proposed provides an essential mechanistic route to equilibrium.

Graphical abstract: A new pathway for the re-equilibration of micellar surfactant solutions

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Article information


Submitted
18 Sep 2012
Accepted
19 Oct 2012
First published
15 Nov 2012

Soft Matter, 2013,9, 853-863
Article type
Paper

A new pathway for the re-equilibration of micellar surfactant solutions

I. M. Griffiths, C. J. W. Breward, D. M. Colegate, P. J. Dellar, P. D. Howell and C. D. Bain, Soft Matter, 2013, 9, 853
DOI: 10.1039/C2SM27154K

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