Dynamic interfacial properties of droplets relevant to W/O-emulsion-forming systems: a refinement measurement apparatus

Dynamic interfacial properties of droplets, as well as mechanical and hydrodynamic processes, play an important role in the formation and stability of emulsions. A better understanding of formation and stability of W/O (and of O/W) macroemulsions requires the acquisition of a deeper knowledge a) of the adsorption dynamics and relaxation processes occurring at single-droplet interfaces and b) of the mechanism of droplet disproportionation and of droplet-droplet coalescence. Thermodynamic models show that molecular processes in adsorption layers, like reorientation or 2D-aggregation, can change the rate of adsorption and the dynamic surface elasticity and viscosity significantly. A change of interfacial (non-equilibrium) composition induces a transient perturbation of interfacial viscoelasticity that influences the contraction of droplets (issuing in Marangoni motion and in possible drop elongation and drop splitting). Also, drop viscoelasticity is a key parameter in the processes of droplet-droplet coalescence. As a significant stage in bringing ahead the scientific comprehension of emulsion behaviour, we conducted measurements of the interfacial dilational modulus and of the interfacial tension relaxation on oscillating millimeter-sized and micrometer-sized drops for water / hydrocarbon systems (as concerns interfacial drop properties, the scaling rule is linear within the macroscopic domain). We used novel experimental methodologies, so that we have access to accurate data on non-equilibrium properties of liquid-liquid interfaces. The poster reports experimental observations of drop viscoelasticity relevant to model hydrocarbon-water-surfactant systems, such as to simulate the composition of the real (complex) emulsions encountered in crude oil industry.