Interactions of cationic surfactant-fatty alcohol monolayers with natural human hair surface: Insights from dissipative particle dynamics

K Sindelka and A Kowalski and M Cooke and C Mendoza and M Lísal, JOURNAL OF MOLECULAR LIQUIDS, 375, 121385 (2023).

DOI: 10.1016/j.molliq.2023.121385

Fatty alcohol (CnFAs) combined with cationic surfactants are common ingredients of lamellar-phase personal care liquids. We employ mesoscopic modelling to study how surfactant-C(n)FA monolayers originating from the corresponding bilayers of the personal care liquids interact with the human hair surface above and below the fluid-gel transition temrerature as well as in- and out-of-equilibrium. For the monolayer model, we consider the single-tail cationic surfacant cetyltnmethylamnmonium chloride (CTAC) and an excess of CnEAs with their alkyl tail length equal to or longer than the CTAC alkyl tail length. The hair surface mimics keratin surface proteins covered by a film of lipid chains covalently bonded to the proteins. Our modelling shows the formation of a dense adsorbed layer due to the interactions of the CTAC and C(n)FA alkyl tails with the hydrophobic hair surface. The adsorption and the behaviour of the adsorbed layer is different under fluid and gel conditions. The differences are related to the structure of the adsorbed layer as characterised by density profiles across the adsorbed layer and the orienrtational order parameters of the chains within the adsorbed layer. Under steady-state shearing (an appronimation of real, non- equilibrium conditions), increasing the shear rate above a threshold leads to continuous or abrupt desorption of the CTAC and C(n)FA chains under fluid or gel conditions, respectively; the desorbed chains can then form various self-assembled structures in the bulk solution. The underlying mechanism of CTAC and C(n)FA desorption from the adsorbed layers is closely related to the corresponding adsorption mechanism. (c) 2023 Elsevier B.V. All rights reserved.

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