Reconfigurable Pickering emulsions Shivangi Chourasia, Catherine Whitby School of Natural Sciences, Massey University, New Zealand
Reconfigurable emulsion systems have emerged as a growing field in colloidal science, offering the ability to control the stability and functionality of emulsions. These systems exhibit responsiveness to external stimuli, allowing for adaptive reconfiguration of the emulsion shape and structure in response to environmental conditions. Advances have been made in developing complex emulsion systems that can controllably be altered after emulsification by stimuli such as temperature, pH, magnetic field and light. 1,2 However, using particles for stabilising these complex emulsion systems remains a critical area requiring investigation and understanding. Reconfigurable emulsions are colloidal systems consisting of two or more immiscible liquids stabilised by particles or stimuli-responsive surfactants, or a combination of both. We have prepared an oil-in-oil-in-water double emulsion using hydrocarbon and fluorocarbon oils. 3 To stabilise the interfaces within this system, we used dimethylsiloxy surface-modified hydrophobic silica particles further functionalised with fluorophilic groups to stabilise the oil-oil interface and sodium dodecyl sulphate to stabilise the oil-water interface. Our research extends the previous findings 3 by exploring how a change in the degree of fluorination of the particles or using oils with different dielectric constants impacts the emulsion configuration. We also investigated how the emulsion behaves with variations in temperature. We are using optical microscopy and confocal microscopy to visualise the changes in the droplet shape and morphology. Altering the polarity of hydrocarbon oils causes the droplet morphology to transition from a nested droplet configuration to a Janus-type arrangement. This transformation can be attributed to an increase in oil-oil interfacial tension with the increase in dielectric permittivity of the hydrocarbon oils. 4 As the temperature increases above the upper consolute point, the hydrocarbon and fluorocarbon oils merge into a single phase. Intriguingly, subsequent cooling of the emulsion leads to the formation of multiple droplets of one oil ensconced within the confines of the other oil. Our overall goal is to design and develop complex Pickering emulsion systems that can respond to stimuli like pH, light, temperature and magnetic fields by reconfiguring in a controlled manner. References 1. Zarzar, L. D.; Sresht, V.; Sletten, E. M.; Kalow, J. A.; Blankschtein, D.; Swager, T. M. Dynamically Reconfigurable Complex Emulsions via Tunable Interfacial Tensions. Nature 2015 , 518 (7540), 520–524. https://doi.org/10.1038/nature14168. 2. Jia, K.; Zhang, X.; Zhang, L.; Yu, L.; Wu, Y.; Li, L.; Mai, Y.; Liao, B. Photoinduced Reconfiguration of Complex Emulsions Using a Photoresponsive Surfactant. Langmuir 2018 , 34 (38), 11544–11552. https://doi.org/10.1021/acs.langmuir.8b02456. 3. Cheon, S. I.; Silva, L. B. C.; Ditzler, R.; Zarzar, L. D. Particle Stabilization of Oil–Fluorocarbon Interfaces and Effects on Multiphase Oil-in-Water Complex Emulsion Morphology and Reconfigurability. Langmuir 2022 , 36 , 7083–7090. https://doi. org/https://doi.org/10.1021/acs.langmuir.9b03830. 4. Morita, M.; Matsumoto, M.; Usui, S.; Abe, T.; Denkov, N.; Velev, O.; Ivanov, I. B. Interfacial Properties and Emulsion Stability in Fluorinated Oil—Non-Fluorinated Oil—Surfactant(s) Systems. Colloids and Surfaces 1992 , 67 , 81–93. https://doi.org/ https://doi.org/10.1016/0166-6622(92)80288-D.
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