Flow-induced states of fluid interfaces decorated with amphiphiles play a central role in phenomena such as emulsification, foaming and spreading. While past studies have shown that interfacial mobility and surfactant reorganization regulate the dynamic properties of fluid surfactant-laden interfaces, few simple methods permit simultaneous monitoring of this interplay. In this paper, we report on the ordering of micrometer-thick films of oils (4-cyano-4'-pentylbiphenyl, 5CB) with liquid crystalline order in contact with flowing aqueous solutions of soluble or insoluble amphiphiles. We observe the onset of flow of soluble surfactant solutions to generate a complex spatial and temporal optical response and show that it can be interpreted to provide insight into interfacial mobility and interfacial surfactant concentrations. Our conclusions are further supported by experiments performed with simple salts and insoluble amphiphiles, which are placed into the context of a model of dynamic LC interfaces. Overall, we conclude that liquid crystalline oils offer the basis of general and facile methods for understanding dynamic behaviors of surfactants at oil-water interfaces and, potentially, for rapidly screening surfactant mixture compositions for desired dynamical properties.

<i>In situ</i> optical mapping of amphiphile reorganization induced by flow at liquid crystal-water interfaces

ACS Spring Meeting 2021

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In situ optical mapping of amphiphile reorganization induced by flow at liquid crystal-water interfaces