Mixing dynamics during coalescence of droplets of complex fluids

Droplet coalescence is a crucial feature of many industrial and natural processes. The focus here is on exciting emerging applications such as reactive inkjet printing. These applications often involve the coalescence of droplets composed of complex fluids (including surfactants, suspensions, reactive species etc) with different material composition and properties. Essential to the success of such approaches is sufficient mixing of the combining droplets, yet this remains poorly understood. This project builds on a successful recently-completed CDT PhD and seeks to explore phenomena not explored in the earlier project. These include thermal effects, chemical reactions, diffusion, rheology, and particularly how these phenomena enhance or hinder mixing at different droplet length scales, from millimetre scale down to inkjet scale (below 100 microns). The specific areas of investigation are flexible and open for the student to decide.

The project is expected to be a combination of theoretical/numerical modelling and experiments, again with the specific balance determined by the student. The computational work will benefit from a previously developed in-house OpenFOAM code as an excellent starting point for further development to include the additional physics required. The former CDT student who completed the previous project will be involved as an external co-supervisor to provide detailed support.

Figure: Computational and experimental observations of the Influence of substrate wettability on internal jet formation in coalescing droplets, as explored in the previous PhD project and published in Langmuir 2020, 36, 32, 9596-9607  https://doi.org/10.1021/acs.langmuir.0c01689