Experimental and Computational Analysis of fluidic interfaces influenced by soluble surfactant

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Surfactants are essential ingredients in many technological processes such as foaming or emulsification. Due to their amphiphilic character they assemble at fluidic interfaces and modify the respective interfacial properties. Since these interfaces are moving and are continuously deformed and expanded, the local instantaneous interfacial tension is a most relevant parameter. In order to obtain a deeper quantitative understanding of such processes with soluble surfactant, this proposal has two general objectives: By means of experimental analysis, employing tools recently developed at the Golm side, complete knowledge of basic adsorption properties for selected homologous series of surfactants at liquid/liquid interfaces will be obtained, performing studies with continuously growing drops and with transient and harmonic perturbations of drops. Since a direct measurement of surfactant distribution lateral at the interface is not possible, a numerical method for the simulation of two-phase Navier-Stokes flows with full resolution of the interface dynamics accounting for the influence of soluble surfactants is highly desired. The development of such a method is proposed here, building on recent preliminary work on the Darmstadt side. While the experimental measurements will provide the parameters required for meaningful simulations, the computational analysis will especially clarify the 3D hydrodynamics in the experiments. Together, the demanded quantitative understanding will be obtained and used to improve and validate simplified models.