The Mathematical Institute, University of Oxford, Eprints Archive

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

Griffiths, I. M. and Breward, C. J. W. and Colegate, D. M. and Dellar, P. J. and Howell, P. D. and Bain, C. D. (2012) A new pathway for the re-equilibration of micellar
surfactant solutions.
Soft Matter . (Submitted)

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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–D¨oring 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.

Item Type:Article
Subjects:D - G > General
Research Groups:Oxford Centre for Collaborative Applied Mathematics
ID Code:1632
Deposited By:Peter Hudston
Deposited On:24 Nov 2012 09:01
Last Modified:24 Nov 2012 09:01

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