Abstract

The concentration of surfactant in solution for which micelles start to form, also known as critical micelle concentration is a key property in formulation design. The critical micelle concentration can be determined experimentally with a tensiometer by measuring the surface tension of a concentration series. In analogy with experiments, in-silico predictions can be achieved through interfacial tension calculations.We present a newly developed method, which employs first principles-based interfacial tension calculations rooted in COSMO-RS theory, for the prediction of the critical micelle concentration of a set of nonionic, cationic, anionic, and zwitterionic surfactants in water. Our approach consists of a combination of two prediction strategies for modelling two different phenomena involving the removal of the surfactant hydrophobic tail from contact with water. The two strategies are based on regular micelle formation and thermodynamic phase separation of the surfactant from water and both are required to take into account a wide range of polarity in the hydrophilic headgroup.Our method yields accurate predictions for the critical micellar concentration, within one log unit from experiments, for a wide range of surfactant types and introduces possibilities for first-principles based prediction of formulation properties for more complex compositions.

Highlights

  • Surfactants are commonplace in society and are the key components in formulated products, such as detergents, cosmetics, fibers,⇑ Corresponding author.oilfield chemicals, pharmaceuticals and food [1,2,3,4,5]

  • The two prediction strategies were tested for a set of anionic, cationic, zwitterionic, and nonionic surfactants

  • The higher polarity of the head groups of ionic surfactants makes the distinction between the hydrophobic carbon chain and the hydrophilic head more pronounced, and it disfavors a ‘‘normal” phase separation into two bulk phases because of the very unfavorable interactions between the hydrophilic and hydrophobic parts of the surfactant

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Summary

Introduction

Surfactants are commonplace in society and are the key components in formulated products, such as detergents, cosmetics, fibers,. Oilfield chemicals, pharmaceuticals and food [1,2,3,4,5]. One property specific to each surfactant is the critical micellar concentration (CMC), which is the concentration of surfactant in water, above which micelles spontaneously start to form. Any nominal increase in surfactant concentration beyond the CMC only leads to the formation of more micelles, while the real surfactant concentration in water remains at the CMC.

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