Materials World Network: Electric Field Induced Microfluidic Manipulation

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This NSF Materials World Network award supports international collaborative research between the Max Planck Institute (MPI) for Dynamics and Self-organization in Goettingen, Germany and Kansas State University in Manhattan, KS. The two groups will collaborate in studying the statics and dynamics of microfluidics in topographically structured microchannels. Microfluidics, the controlled manipulation of microliters or nanoliters of liquid or liquid solution in closed channels or on a substrate surface is gaining increasing technological importance with the creation of chemical factories on a chip, fast variable focal length optical liquid lenses and high visibility video speed electronic paper. This liquid manipulation is frequently controlled via the use of electric fields and in particular via the electrowetting effect, which controls the contact angle of droplets on surfaces. Currently it is not well understood how the interplay of electric field effects, wetting layers, surface slip, surface topography of the substrate and liquid morphological instabilities combine to govern the time dynamics of liquids in topographically structured channels. The influence of wetting layers and surface slip on planar surfaces and how they are changed by the presence of an electric field and/or liquid shear will be studied in Kansas. Uniform wetting layers are predicted to undergo an electrohydrodynamic instability (and break up into nanodroplets) for sufficiently large electric fields where the additional effects of liquid shear play an unknown role. Uniform wetting layers, surface nanodroplets or electric field induced surface ordering is expected to influence the slip behavior found at solid/liquid interfaces. The MPI group in Goettingen will study the interplay of surface topography during electrowetting and how this topography influences the time dependent liquid filament spreading down microfluidic channels, as well as, liquid morphological instabilities from liquid filaments to liquid droplets within these channels. There will be frequent exchanges of personnel between the two groups because the presence of wetting layers and slip (studied in Kansas) will play a major role in governing the time dependence of both the spreading and morphological break up in microfluidic channels (studied in Goettingen). These exchanges will strengthen and enhance the educational, cultural and international cooperation between the two groups. The proposed research will provide the fundamental foundations for a better understanding of the static and dynamic electrical manipulation of liquids in topographically structured microfluidic devices. This information is expected to be of significant practical use for many different fields in microfluidic device design. The counterpart project is funded by the German National Science Foundation (DFG).