The dynamics of droplets and bubbles suspended in a liquid has a direct impact on the properties and performance of multiphase emulsions and foams. The dispersed phase is often stabilized by surface active compounds such as surfactants, resulting in highly complex chemical compositions and material properties at the fluid-fluid interface. In this talk, recent advancements in the use of microfluidic flow fields will be highlighted for measuring the collision, coalescence and film drainage between two surfactant-laden droplets. Microfluidic expansion-contractions, cross-slots, and traps are used to study the droplet dynamics, across a range of viscosity ratios and surfactant concentrations, both with and without channel confinement. Results are quantified as a function of non-dimensional film drainage time, confinement ratio, surfactant concentration, and capillary number. This enables the evaluation of the influence of interfacial mobility and Marangoni flows on film stability with soluble surfactants.

Impact of interfacial mobility, Marangoni flows, and confinement ratio on the micro-scale droplet film drainage time

ACS Spring 2022

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