In this project computer simulations are used to reveal the impact of a crucial underlying phenomenon: little waves on the surface of droplets that can suddenly grow and thus accelerate coalescence.
Emulsions of little droplets originate from intensive contacting between, for instance, oil and water. It is important for applications to have these little droplets coalesce into larger droplets again, in order to allow separation of the oil and the water. Currently, we are unable to predict how droplets coalesce.
Stability of emulsions
Controlling the stability of emulsions is key to many industrial processes. It is crucial in, for example, food, formulation, and separation technology.
This control, however, is obstructed by the lack of accurate models to predict how long it takes for droplets to coalesce under industrially relevant conditions. Existing scaling rules have been found to be incorrect, even qualitatively. An important step forward is to include new physics that are currently missing in the description of droplet coalescence: the capillary waves on the interfaces that are caused by thermal fluctuations.
Although the existence and importance of thermal fluctuations have recently been proven for other processes involving thin films, so far their role has not been revealed for the dynamics of the thinning and rupture of the film between emulsion droplets. This is where the proposed work makes a difference.
Understanding coalescence of emulsion droplets
The goal of the proposed work is to understand coalescence of two emulsion droplets, revealing the role of thermal fluctuations, and addressing non-ideal fluids, surface-active species, and realistic droplet contacting.
Improved scaling rules
Our approach is inspired by work on physically similar thermal effects at interfaces, where new numerical methods have vastly improved the description of the spreading of droplets and de-wetting of coatings in
idealized situations. We propose to use stochastic simulations of the process that include, from first principles, the thermal fluctuations that ultimately cause film rupture.
The robust and accurate integration of the stochastic non-linear differential equations is challenging. However, one of the key advantages of this approach is that the many simplifications required to, for example, make analytical progress are no longer needed.
If successful, this work not only yields an improved understanding of coalescence in emulsions, it also provides scaling rules that can be used to model coalescence at the scale of process equipment.
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This project is co-funded by the Dutch Research Council (NWO) and TKI-E&I with the supplementary grant 'TKI- Toeslag' for Topconsortia for Knowledge and Innovation (TKI’s) of the Ministry of Economic Affairs and Climate Policy.