Multicomponent amphiphilic systems containing oil, water, and surfactants have been widely utilized in applications ranging from oil recovery and drug delivery, to food and personal care products. The main role of surfactants in those systems is to increase emulsion stabilities and control colloidal morphologies. Here, we present a method for the in situ formation of a nanostructured interface between an aqueous cationic surfactant (cetylpyridinium chloride) solution and a fatty acid (oleic acid, OA). We study the underlying mechanisms for the formation of the surfactant/fatty acid self-assembly at the interface, and characterize the nanostructure using small-angle X-ray scattering (SAXS). We show that the interfacial layer can undergo hydrodynamic instabilities with interplaying component concentrations and flow conditions. It is evidenced that the hydrodynamic instabilities of the interfacial layer are highly influenced by the phase equilibria of three-component amphiphilic system, even though the interfacial layer forms far from equilibrium conditions. The correlation between characteristics of the in situ interfacial layers and those of equilibrium phases can help to predict the interfacial instabilities. The work presented here has implications for controlling and optimizing the morphology in wide variety of complex fluid systems including surfactant mixtures, emulsions, and colloidal domains.

Hydrodynamic instabilities in fatty acid/surfactant self-assembling systems

2019 Fall National Meeting

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