Interview

The goal of this SRO is to combine fundamental research on the behaviour of fluids in confined space with research that focuses on chemistry in fluids in contact with surfaces, and to translate that into applications.

Specific applications that can be thought of are micro reactors for the screening of chemical processes. My vision is not that in future we’ll do all the chemistry in small channels that some people think and claim as a disadvantage because such channels might clog easily.

I rather think that the concepts that apply on a small scale should be replicated to the larger systems. The term "replicated" can be taken literally here, by using the fabrication possibilities of state-of-the-art micro and nanotechnology.

To come to innovative products and other applications, we should start with the real fundamental physics. I am thinking of the interaction of ultrasound with gas bubbles as studied by professor Detlef Lohse for instance. One example of an interesting concept is the use of an oscillating bubble attached to a surface, on which I have collaborated with Sascha Hilgenfeldt and Philippe Marmottant, former co-workers of the Physics of Fluids group. Accidentally they discovered that the flow around such a bubble becomes asymmetric when there is a solid particle near. We made a structured surface with bumps and hydrophobic pits to which bubbles can be attached, which is the underlying principle of a ‘liquid flow creator’. The concept may be used to sort for example nanoparticles of different size, or living cells of different flexibility, like cancer cells from healthy cells. Another topic on which I will work together with Lohse's group is the stimulation of chemical processes in a liquid by collapsing gas bubbles, a principle that is called "sonochemistry"

Another example could be the work of Frieder Mugele, who is also participating in this SRO, using the principle of electrowetting. Electrowetting changes the properties of hydrophobic surfaces, on which droplets sit as spheres, by either contracting droplets or spreading them out. This fundamental principle may lead to self cleaning surfaces for instance.

The third main group that is involved in this SRO is the team of Matthias Wessling, who is working on microstructured membranes and plastic microreactors. A topic that we may study is the creation of specialized emulsions using these membranes.

The advantages of a Strategic Research Orientation platform, is the combination of fundamental research and working towards applications; in food, the medical environment and other areas. My background, besides physics and chemistry, is Micro Fabrication – and I think I can make a link there by helping with the translation of fundamental ideas into device designs. Although it is not a real policy of the university, I do hope to patent some new concepts. Perhaps this makes this SRO more technological than fundamental, but I would like to emphasize that the fundamental input cannot be spared on order to find new directions.

Another thing I look forward to doing is to bridge the gaps that exist between disciplines.

If, for instance, we look at the micro/nano structured reactors and liquid chromatography chips, we see that they are being used for chromatographic analyses; but the same structures could also be used as reactors if a catalyst is put on them. They can also be used for heat exchange, either to heat or to cool liquids, as is done in Marcel ter Brake's group you could use them for filtering or emulsification, etc. What I see in literature however is that researchers from the different disciplines do not know that some of their problems have already been solved in other areas. They publish in different journals and apparently they do not read each others work. That is a waste of resources I would like to do something about.’

[January 2006]