Publications
Wetting gradient induced separation of emulsions: A combined experimental and lattice Boltzmann computer simulation study
F. Varnik, P. Truman, B. Wu, P. Uhlmann, D. Raabe, M. Stamm.
Physics of Fluids, American Institute of Physics, 20, 072104, 1-14, (2008)
Abstract
Guided motion of emulsions is studied via combined experimental and theoretical investigations.
The focus of the work is on basic issues related to driving forces generated via a step-wise (abrupt)
change in wetting properties of the substrate along a given spatial direction. Experiments on binary
emulsions unambiguously show that selective wettability of the one of the fluid components (water
in our experiments) with respect to the two different parts of the substrate is sufficient in order to
drive the separation process. These studies are accompanied by approximate analytic arguments as
well as lattice Boltzmann computer simulations, focusing on effects of a wetting gradient on internal
droplet dynamics as well as its relative strength compared to volumetric forces driving the fluid
flow. These theoretical investigations show qualitatively different dependence of wetting gradient
induced forces on contact angle and liquid volume in the case of an open substrate as opposed to a
planar channel. In particular, for the parameter range of our experiments, slit geometry is found to
give rise to considerably higher separation forces as compared to open substrate.
Keyword(s): lattice-boltzmann; microfluidics; separation phenomenon; demixing; capillarity; surface tension
DOI: 10.1063/1.2963958
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