Authors: P. Truman, F. Varnik, P. Uhlmann, M. Stamm and D. Raabe
Affilation: Institute of Polymer Research, Germany
Pages: 280 - 283
Keywords: fluid transport, flow, fluidic device design, micro fluidic devices, fluidic device simulation
We study how chemically patterned surfaces can be applied for the separation of two incompatible liquids and introduce a novel simplified separation scheme utilizing surfaces with an abrupt change of surface energy. Firstly we analyse general aspects of the separation process on such surfaces and define the following fundamental process steps: the surface energy change induced liquid movement (1), capillary drop attraction of media 1 through media 2 (2), the drop to drop impulse transfer of merging droplets (3) and the push away effects (4). Secondly we demonstrate the separation based on these processes: A Toluene/Water-mixture is separated in a microfluidic cell milled into a teflon block with a cavity filled with epoxy resin. While the wetting of Toluene is just slightly influenced by hydrophilicity/-phobicity water selectively wets the surfaces. Compared to a surface energy gradient the abrupt change of surface energy enhances the surface induced liquid movement. To shade a glance on the dynamics of merging droplets (3) we use acid-base-indicator systems to visualize liquid flow. Furthermore it is shown that Lattice Boltzmann (LB) Simualtions enable to model relevant processes such as droplet coalescence on surfaces with the surface wettability as an imput parameter. Finally we discuss the impact of surfactants as intermediate layers and the influence of confinement on the process.