Lingling Shui (promotion date: 14 May 2009)

Two-phase flow in micro- and nanofluidic devices

Promotion date: 14. May 2009

Promotor: Prof. Dr. Albert van den Berg

Assistant promotor: Dr. Jan C. T. Eijkel

Micro- and nanofluidic devices were investigated for the creation and manipulation of oil and water systems, and for the production of femtoliter-size droplets.

This thesis provides experimental data and theoretical analysis on two-phase flow in devices with different layouts of micrometer and nanometer sized channels.

To investigate the role of interfacial forces: solid-liquid and liquid-liquid interfacial tensions and nano-micro fluidic geometry (dimension) were modulated.

Did you experience a specific moment during your thesis project, when you achieved a good result?

One was at a micro-TAS conference. A colleague presented a pressure controlled dynamic flow for particle separation. This principle I used in my investigations later on.

Even stronger was the moment, when I saw the expected interfacial tension controlled droplet formation, using nanochannels. It was even more beautiful as expected. I could see many tiny (nm~μm) monodisperse droplets packing together over a length of several molecules.

Do fluids and solids behave differently at nanoscale?

Yes, they are different at the nanoscale. The interfacial tension becomes increasingly important as downscaling. For example, at very low flow rates, we obtained a regime in which droplet formation is solely determined by capillary instability in microchannels, due to the device geometry, independent on flow rates and liquid properties.

Furthermore, the behaviour on nanoscale can be very different than it is on macroscale. For example, a very complex system, like milk, could behave more stable, and more quickly, when you transport it in very small and monodisperse droplets using nanochannels.

Are your experimental, and theoretical, results important for new lab-on-a-chip designs?

Yes, I believe my rather fundamental study will lead to an application approach, for example single molecular detection. Also chromatography seems feasible when the packing process of well-patterned droplets in an exact dimensioned channel design is further optimized.

I stay for three more years to work as a post-doc. But my main goal is to work on microfluidic devices to manipulate biomolecules, for example DNA.

In the more far away future, do you like to be a researcher still?

Definitely. Research is hard work and it can take some time before you reach a nice result. But the exciting moment is really exciting. It is worth the effort you put in.

How did you experience working at MESA+?

Our group is very multidisciplinary and above all, it is an open and really nice social environment. It is easy to discuss all kind of topics, from different angles. Together with the help of the professors, you have all possibilities to carry your research further.

Also the facilities available in the MESA+ cleanroom, and the professional assistance there, are great.