(381c) In Situ Optical Mapping of Interfacial Mobility and Amphiphile Concentrations at Liquid Crystal-Water Interfaces

Flow-induced non-equilibrium states of surfactant-laden interfaces play a pivotal role in interface engineering such as emulsification, foaming and spreading. Although many past studies have demonstrated that the dynamic properties of fluid interfaces decorated with surfactants are regulated by interfacial mobility and surfactant reorganization, few methods permit simultaneous monitoring of this interplay. In this presentation, we will report on the optical responses of micrometer-thick films of liquid crystalline oils (4-cyano-4´-pentylbiphenyl, 5CB) in contact with flowing aqueous solutions with amphiphiles. We observe the flow of solutions of soluble surfactant to generate a transient and spatial optical response in the 5CB oil film, which we interpret to provide insight into interfacial mobility and interfacial surfactant concentration gradients. Experiments performed with simple salts and insoluble amphiphiles, which are placed into the context of a model of dynamic LC interfaces, are used to provide further support for our conclusions. Overall, we conclude that liquid crystalline oils provide the basis of general and facile methods to understand the dynamic behaviors of surfactants at oil-water interfaces and, potentially, to enable rapid optimization of amphiphile mixture compositions for targeted dynamical properties.