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Seminars
Crystal Comets: Dewetting during Emulsion Droplet Crystallization
Patrick T. Spicer
Complex Fluids Research
Procter & Gamble, Co., West Chester, Ohio
When: Thursday, March 22, 2007
Time: 2:30 PM to 3:30 PM
Where: 1070 Duncall Hall
Abstract:
Oil-in-water emulsions are excellent substrates for synthesizing biomimetic, photonic, encapsulations, and unique colloidal materials,, while crystallization of emulsions is used to create consumer product microstructure and to purify small molecules and proteins. Crystals formed within an emulsion can partition at the oil-water interface and stabilize an emulsion against coalescence, destabilize it by partial coalescence, or even leave the droplet entirely depending on their wettability. Previous work on crystal wettability in emulsions only examines partially crystallizing emulsions with a focus on equilibrium crystal partitioning and long-time instabilities while the dynamics of crystal wetting receive little attention. A unique and unstudied case is when the nitre droplet crystallizes while simultaneous rapid dewetting occurs on the same time scale. Such a case offers a new approach to controlling the morphology of particles formed from emulsion droplets. Here we show (using numerous microscopic movies) that liquid oil emulsion droplets can violently dewet their own solid crystals during crystallization as a result of surfactant adsorption. The crystal shape formed is a function of the relative rates of dewetting and crystallization as controlled by surfactant adsorption, cooling rate, and lipid purity. For negligible dewetting rates, crystals nucleate and grow within the droplet. At similar crystallization and dewetting rates, the droplet is propelled around the continuous phase on a crystalline "comet tail" much larger than the original droplet. Rapid dewetting causes the ejection of small discrete crystals across the droplet's oil-water interface. Applications in colloid synthesis, molecularly aligned materials, and separations will also be discussed.
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