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Hao Gu (promotion date: 18 March 2011)

Controlling two-phase flow in microfluidic systems using electrowetting

Promotion date: 18. March 2011

Promotor: Prof. Dr. Frieder Mugele

Assistant promotor: Dr. Michel H. G. Duits

The aim was to investigate a novel concept of hybrid microfluidic chips which combine the strengths of pressure-driven, two-phase flow microfluidics and the unique control possibilities offered by electrowetting (EW) technology.

To achieve this goal, several such hybrid microfluidic chips were designed and developed, using different approaches. Also the functionalities of such chips have been explored and demonstrated.

The formation of droplets occurring only upon EW actuation in the specific region, was presented. Based on this theory, an innovative microfluidic platform was designed, able to implement voltage programmable on-demand formation and merging of droplets. This platform can be used in microreactors and in biosensors.

Later on, a flexible droplet generation method was demonstrated, using both EW and pressure controls in a downscaled device. This approach offers potential use in emulsification.

Furthermore, a tensiometric device based on a microfluidic tapered channel, was designed.

Is your research aimed towards application?

It certainly is. Nevertheless, some major topics still need extra investigation.

Using electrowetting technology, for example, I showed that the water-oil interface can change with tuning applied voltages. This outcome can be of importance to build new droplet based microfluidic systems, for example to produce droplet-on-demand, and merge them very efficiently.

This is an application very relevant for academic research and even so for several medical applications and research ends. To make these applications possible, however, labs-on-a-chip have to be designed and tested in such a way.

Another interesting feature of droplet control, is in food industry. Droplet/bubble sizes effect the taste sensation of most food products.

So, you like to contribute to society as a researcher?

Indeed, I do. I like to work at a R&D department of a company in research aimed at applications, be it in China or in Holland. I am thinking of these countries, as I have a family now with my daughter born last year.

The research performed in the thesis project was sponsored by MicroNed, involving companies like Akzo Nobel, Océ, Friesland and also the Dutch government.

In what way did you develop personally, as a scientist/researcher in this period?

Coming from a chemical engineering background I broadened my knowledge a great deal, learning about the reactions and phenomena taking place in the actual electrowetting process, for example. I received much support from fellow researchers and PhD’s on this.

I enjoyed working in the nano lab even more, as I consider myself an experimentalist. I like to improve my experiments step by step, performing a lot of different types of them, not only analyzing things by using the computer.

Were your findings published?

I had six articles published, among them the Journal of Lab-on-a-Chip, and Applied Physics Letters. Also I had one proceeding on a conference in the Netherlands.

What, in your opinion, is needed for Mesa+ to stay successful in the future?

Mesa+ could be more well-known in the US and in Asia, I suppose. A way to reach this goal is to invite leading speakers to Mesa+.