Tailoring emulsions of complex fluids for precise wetting and coalescence rates

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An emulsion is a mixture of two immiscible liquids in the form of drops of one liquid suspended in the other. In spite of being ubiquitous in everyday life and in the industry, emulsions are still being formulated largely by combinatorial methods, due to a lack of the fundamental relationships that connect their composition, processing and structure to their properties. This project aims to remedy this gap in the literature for two important emulsion-related phenomena: wetting, which is the spreading of an emulsion drop on a surface, and coalescence, which is the union of two drops into one larger drop. ***In many applications, it is critical to tune the coalescence and wetting rates to achieve the desired product properties or specific functions. But while there are several studies explaining thermodynamic aspects of wetting and coalescence, investigations of the rates at which these phenomena occur are sparse. Emulsion-based products form a billion dollar industry, hence any improvement in the fundamental understanding with respect to these two key phenomena can lead to substantial benefits to the industry.***The emphasis of our coalescence and wetting studies will be on a class of fluids called complex fluids. These fluids are Jekyll and Hyde fluids, and can behave like solids or liquids depending on how stresses are imposed on them. Coalescence and wetting are least understood for these materials, in spite of the fact that most industrial emulsions are made out of complex fluids. In this work, we will focus on three complex fluids: polymer melts in the context of polymer blends, surfactant solutions which are used extensively in emulsion formulations for specific spreading properties and for stability against coalescence, and yield stress fluids which are used to stabilize emulsions against gravity.***To unravel the governing mechanisms and time scales of coalescence or wetting for these complex fluids, we will employ the Cantilevered Micropipette Device (CMD) in conjunction with an optical technique called Reflection Interference Contrast Microscopy (RICM). The CMD will allow us to measure the force between a drop and a solid-fluid or fluid-fluid interface down to a fraction of a nanoNewton. Simultaneously, we will measure the film contact profile down to a nanometer using RICM, and supplement the data with cryo-Scanning Electron Microscopy wherever possible. ***The knowledge and tools from this work will allow us to quantify the rates of coalescence and surface wetting in emulsions composed of complex fluids, facilitating emulsion design with preselected wetting and coalescence times and allow a transition away from the current empirical design paradigm. There are several emulsion-based industries in Canada, and each of these is, at least, a multimillion dollar industry. When HQP trained in our lab in state-of-the-art methods join the workforce, they will provide Canadian industry a huge competitive edge.