Interfacial Rheology and Morphology
	OilBAM and DropBAM: Experimental investigations on the rheology and structure of surfactant assemblies at the planar and curved liquid-liquid interface
	The flow of fluids composed of immiscible mixtures of two or more phases, is of interest in a wide range of research fields, such as foods, polymers, pharmaceuticals and cosmetics. To produce and stabilize such products amphiphilic molecules, i.e. emulsificators (emulsions, microemulsions, multiple emulsions and suspension) or compatilizers (polymer blends, composites) are used. By adding such surface acting components one is potentially able to alter the physical and chemical properties (viscosity, elasticity, surface tension) of the interfaces in defined ways. For the stability, performance and quality of multiphase products the interfacial film, its structure, interfacial tension and rheological properties are considered to be strongly relevant. In particular, the rheology of the interfacial film has a significant influence on emulsifications, emulsion stability, foam stability and de-foaming. Also the self- orientation of surfactants under non-equilibrium condition is of extreme importance since it results in complex changes in morphology (phase behavior, domain structures and viscoelasticity). Focussing on liquid-liquid interfaces (droplets) the manifold interaction among interfacial rheology, interfacial structure together with flow stresses acting on the deformable soft surfaces, time-dependent concentration gradients in planar (e.g. Marangoni effect) and three dimensional phases, transport phenomena, and adsorption kinetics are of interest. In addition, the coupling of the interfacial flow with the flow of the subphase can imprint additional orientational properties on the interfaces domain structure that, in consequence, can influence the drop deformation and break-up, respectively. In summary, knowledge of the structural and rheological can provide insight into molecular interactions and organization at the interface and, therefore on emulsification processes. To date, precise quantitative and qualitative information about this influence is limited. Since fluid phase boundary are present in many materials a strong interest and need for obtaining such information has made soft interfaces and their rheology a key area of research in multiphase fluids. Within the proposed research project, the rheology and morphology of planar and curved liquid-liquid interfaces with and without amphiphilic molecules (clear and covered interface) will be studied quiescent and as a function of in-flow conditions. As analytical methods modified BAM set ups and a interfacial rheometer will be used in combination with flow cells that can imprint 2D mixed shear and elongational flow in the planar or curved interfaces (droplets) and also allows investigation the influence of complex 3D flow on such 2D planes. Main focus will be single drop systems that are fixed in these specific flow geometries similar to those already developed by the applicant. The objectives to be investigate are as follows:
	The microscopic local behavior and structure of clean and covered liquid-liquid interfaces (nonsoluble surfactant or emulsifier layer).
	Investigation of the rheological properties of the planar liquid-liquid interface with and without a flowing subphase (coupling to the bulk phase, Boussinesq flow).
	Investigation of the flow induced time dependent surfactant concentration gradient on planar and curved (droplets) interfaces in rest and under non-equilibrium situations.
	Investigation of domain structures and viscoelasticity assuming a non-homogeneous coverage and non-Newtonian rheology of the interfacial layer.
	Transport phenomena and adsorption kinetics of the surfactant. Organization including anisotropic orientation at the interface under flow. With a strong background in droplet flow and dispersing techniques the applicant aims to investigate the planar and curved liquid-liquid interface (droplet) with rheological and structural techniques where the applicant has work for several years and has established profound knowledge. The combination of both well-established research areas allows to investigate systems in the quiescent (OilBAM) or under flow condition (DropBAM) and to correlate rheological to morphological properties. Unique results can be expected from this combination techniques and materials as:
	New experimental techniques as surface rheometry in conjunction with morphology characterization by modified Brewster Angle Microscopy (BAM).
	Understanding the structural, morphological, chemical, and physical properties of liquid-liquid interfaces (microphysics of the soft interface).
	Understanding surfactant flow and morphology under real process conditions (effect of surfactant concentration, concentration gradient (Marangoni effect), and structure on deformed interfaces).
	Dr. Peter Fischer (peter.fischer@ilw.agrl.ethz.ch)