Critical micelle concentrations in surfactant mixtures and blends by simulation

The move towards sustainably sourced raw materials in the $multi-billion surfactants market is driving innovation in the fast-moving consumer goods sector, for example cleaning products for home and personal care use.  For optimal performance, products are usually formulated around surfactant mixtures, and the raw materials themselves are often blends, hence there is an urgent need to revisit the characterisation of these systems and bring modern computational tools to bear on the problem.  Brute-force simulation permits interrogation of solution state in unprecedented detail but is not necessarily convenient to predict properties such as the critical micelle concentration (CMC).  In this work, we combine brute-force simulation at concentrations well above the CMC with traditional thermodynamic pseudo-phase separation (PSM) modelling to predict the CMC as a function of composition; the fitted PSMs can then easily be applied to multicomponent mixtures.  We illustrate the approach with detailed calculations for sodium laureth sulphate (SLES) surfactants with dissimilar ethoxylate spacer lengths.

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