Dynamics of Morphological Wetting Transitions on Topographic Substrates

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We propose to exploit the variety of liquid morphologies forming on topographically structured substrates for manipulating small amounts of liquids on that substrate (open microfluidics). Using the electrowetting effect, we plan to transport liquids on a substrate bearing appropriate steps and grooves, by switching between various equilibrium morphologies of the free liquid surface. The particular advantage of topographic substrates is the variability in the Laplace pressure of the emerging liquid morphologies, such that liquid may be taken even from a zero pressure reservoir. We want to study the impact of a variety of parameters on the liquid morphologies, such as the applied (ac-) voltage, its frequency, the thickness of the insulating substrate coating, and the topography of the substrate. Particular emphasis will be on the interplay of the intrinsic deformation of the surface profile due to electric fields in the vicinity of the contact line and the external deformation due to the confinement in a groove. The liquid morphologies will be observed using atomic force microscopy and confocal fluorescence microscopy.