In this thesis the evaporation and dissolution of droplets in multi-component systems was central. ‘Quantitative understanding is important in many applications,’ says Huanshu Tan. ‘As examples serve: inkjet printing, liquid-liquid extraction, DNA mapping and emulsion formation.’
The evaporation and dissolving processes of “ouzo” were explored, in which water, ethanol and anise oil are present. ‘In my research, I used different experimental techniques,’ Huanshu says. ‘Confocal microscopy, micro-particle image velocimetry, fluorescence techniques, and high-speed imaging techniques. These techniques were combined for the research, adding details to the knowledge of fluid mechanics.’
Interesting microdroplet nucleation triggered by the evaporating “ouzo” droplet, was observed. This spontaneous nucleation phenomenon also occurred in dissolving ouzo droplets.
‘The collaboration with colleague researchers specialized in numerical analyses was very inspiring,’ Huanshu says. ‘It led to advanced experimental setups. Because of the valuable exchange, we gained in-depth factors to the hydrodynamics inside the evaporating droplets, including: preferential evaporation position, evaporative cooling effects and understanding of Marangoni flows. We proposed a generalized diffusion model.’
Many other interesting phenomena were discovered in these ternary systems including: self-forming oil rings at the droplet contact line; wrapping of nucleated oil, and suspending microdroplet rings.
Huanshu can see clear future applications arising for this field of research. ‘A new evaporation-driven particle fabrications strategy shows clear advantages, for example,’ he says. ‘Further, the appearance of self-formed lubricating oil layers conduces to the complete detachment of the generated supraparticles, which allows repeated utilization of the surfaces.’
Huanshu believes this approach of particle synthesis has many advantages including: scalability, flexibility, operability, cost-efficiency and chemical-consumption-efficiency. ‘This will give tremendous contributions to the mass production of advanced particles,’ thus Huanshu.
‘The last part of my PhD project was concentrated more on the application potential. For example, the control over area-volume ratios, can become an important feature for the fabrication of future catalysts. Also, we used the solvent exchange method, to form surface nanodroplets in a narrow channel with controlled flow conditions.’
Regarding his future work, Huanshu favours a career in academics. ‘The mix of interesting topics and questions will keep me inspired for a longer period of time,’ he shares. ‘My next step will be to work as a post-doc at the University of California – Santa Barbara. Here I will focus on even smaller droplets and their interactions.’
‘The focus will be on physical properties as well, and its influence on chemical engineering processes. In the more far away future, I would like to return to China and hopefully start a Group their on this research field.’
Huanshu was happy to be a Mesa+ researcher. ‘It allowed me to focus on other disciplines as well, and integrate these expertise fields and experimental techniques into my own work,’ he says.
‘Chemical engineering and materials science are present within Mesa+. I am glad to have brought some of their ideas into the Physics of Fluids Group. When showing my poster presentations and giving talks at the annual Mesa+ Day, I felt appreciated. From the conversations some inspiring thoughts and contacts emerged.’