Effects of 1-hexanol on C₁₂E₁₀ micelles: a molecular simulations and light scattering study

The micelles of the non-ionic C₁₂E₁₀ surfactant and 1-hexanol as an aqueous solution additives are studied toward the purpose of understanding the role of alcohol additives in tuning the characteristics of alkyl-ethoxylate micellar systems. Our dynamic light scattering and cloud point experiments show that the addition of hexanol induces a response similar to an increase of temperature. We associate the change with increased attraction between the micelles at low to moderate hexanol loadings and a potential increase of the aggregate size at a high hexanol-to-surfactant ratio. Detailed molecular dynamic simulation characterization shows that hexanol solubilizes to a micelle palisade layer when the hexanol-to-C₁₂E₁₀ ratio is less than or equal to 0.5 while swollen micelles, in which a part of hexanol forms an oil core, are present when the ratio increases above approximately 1.5. The simulations indicate that the surface of the micelles is rough. Formation of reverse hexanol structures akin to those found in bulk octanol is observed in the oil core. Molecular simulations associate the increase in attraction between micelles observed via the experiments with decreased chain density in the headgroup region. This density decrease is caused by hexanol molecules solubilized between neighbouring surfactants. Altogether, these findings provide detailed physical characterization of the effect of an archetypal solution additive, hexanol, on an alkyl ethoxylate micelle system. These findings could bear a significance in designing micellar and emulsion based systems with desired solution characteristics or properties for e.g. drug delivery, catalysis, or platforms for green chemistry reactions.