Abstract
Polymer stabilized emulsions are commonplace in industries ranging from cosmetics and foods to pharmaceuticals. Understanding the physical properties of emulsions is of critical importance to the rapid advancement of industrial applications. In this work, we use a sessile drop geometry to examine the effects of viscosity changes of the surrounding glycerine/water solution on polystyrene-b-polyethylene oxide (PS-PEO) covered toluene droplets. In the experiment, emulsion drops are driven by the buoyant force into a smooth mica surface. The drops buckle as they approach the mica, trapping some of the outer fluid which slowly drains out over time. The characteristic time of the drainage process as well as the surface tension was measured as a function of glycerine/water concentration. The surface tension is found to have a minimum at a glycerine concentration of approximately 50% (by weight to water) and the drainage rate is shown to be well described by a recent model. The simple experiment not only shows how critical features of emulsion stability can be easily and reliably measured, but also identifies important new features of the drainage process.
Highlights
Emulsification is the process in which two immiscible fluids are mixed together to create an ensemble of small droplets of fluid A in a matrix of fluid B
We find that many of the drawbacks can be overcome by using the sessile drop technique [15]
We focus on altering the viscosity of the surrounding fluid by changing the ratio of glycerine to water and examining its effects on the droplet dynamics
Summary
Emulsification is the process in which two immiscible fluids (say A and B) are mixed together to create an ensemble of small droplets of fluid A in a matrix of fluid B. Applications can be as simple as making mayonnaise by emulsification [1,2] and stabilizing oil with particles [3,4,5], or as complicated as encapsulating and delivering a specific drug to a specific location within our bodies [6,7,8], and making superhydrophobic surfaces [9,10] Many of these processes use amphiphilic polymers as they form an attractive synthetic system in which responsivity can be engineered (for example to rupture droplets under some stimuli)
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