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Dileep Mampallil (promotion date: 22 September 2011)

Microfluidic flow driven by electric fields

Promotion date: 22. September 2011

Promotor: Prof.dr.ir. Frieder Mugele

Assistant promotor: Dr. Dirk van den Ende

This thesis deals with flow in microchannels and in small drops, controlled by electric fields. Gate electrodes embedded in channel walls control the electro-osmotic flow in microchannels. The flow can also be controlled by chemical modification of the zeta potential of the channel walls with a cationic polymer.

An analytical model is described to quantify the electro-osmotic flow velocity and determine the surface charge on the microchannel walls from the measured current behavior.

Sessile and sandwiched drops are studied. Flow-fields inside the drop not only mix the liquid but are also able to generate pre-concentration of dispersed particles near “pinning sites”. Locally the particle concentration is increased inside the drop by a factor of about ten.

The oscillatory behavior of drops sandwiched between two hydrophobic glass plates is also studied.

Was there a special moment that you remember?

After two years in my project, we decided to include the study of droplets into the thesis project because we wanted more. Flow inside droplets is an important feature in mixing. We managed even to de-mix i.e. to concentrate dispersed particles inside the drops. These experiments were very exciting.

Did some publications come out of your research?

Publications appeared in Electrophoreses, Soft Matter and Applied Physics Letters. Also I spoke on conferences in the MicroNed programme. Four more publications are underway at this moment.

How did you develop personally, as a researcher and scientist?

Basically I am an experimentalist. In the thesis project, I learned to perform good experiments, analyze, interpret the results, and compare them to literature, all the way through. The work differs essentially from the master project. A lot of things you have to find out yourself, as you are not aware of the process steps yet to come, not being sure if results will appear. You have to modify your experiments time to time to obtain the desired results.

My experimental skills did grow a great deal. On a personal level, I am much more outgoing now, managing the project steps independently. Also my presentation skills are improved.

What are your future plans?

Right now, I am working as a post-doc in Nano Ionics group. Although the basics are comparable, quite different skills are involved, mainly electro-chemistry. In nanotechnology chemistry and physics are mixed anyway.

In future, I prefer an academic career because you can choose yourself what kind of research to perform. I don’t focus on academics alone, and keep all possibilities open.

What, in your opinion, is important for Mesa+ to stay successful?

The University of Twente is young. Nevertheless, Mesa+ is very famous. That is a good result, made possible by talented people able to make use of the most high-tech facilities. Both are important as a basis for success in nanotechnology.