Development of an Experimental Device for the Assessment of Emulsions Dynamic Behavior and Stability in Micro-gravity

Abstract

Emulsions are encountered in foods, cosmetics and pharmaceuticals. Their stability depends strongly on gravity (creaming or sedimentation) and interface driven destabilization mechanisms (coalescence or aggregation) occurring after their production. Although of great significance, coalescence and aggregation cannot be studied in-depth on ground due to coupling with gravity driven mechanisms. To overcome this restriction, the design, development and preliminary testing of a new experimental device to be used in the forthcoming ESA parabolic flights for the evaluation of emulsion dynamic behavior and stability under low gravity conditions, is presented. Such conditions allow to get rid of creaming and sedimentation and, thus, to isolate droplets coalescence and aggregation. A novel miniature emulsification cell, along with advanced electrical and optical diagnostics to produce and investigate emulsions are incorporated to custom experimental cells. Optical diagnostics include a high speed camera (up to 750.000 fps) to monitor droplets breakup and droplet-droplet interactions and a high resolution DSLR camera (20MP) to determine droplet size distribution. The EU patented I-VED electrical impedance spectroscopy technique (EP 3 005 942 A1, 2016) is employed to monitor the evolution of oil volumetric fraction as a function of time and gravity. Experimental parameters under study include: oil volume fraction, surfactant concentration, pulsation duration and stroke frequency for emulsification. The implementation of the experimental device, including two racks and one baseplate, complies with ESA technical requirements and safety regulations, while a number of experiments on-ground with a conventional oil-in-water emulsion validates it from a technical and functional point of view.