Keywords: open-channel microfluidics
Summary:Open Microfluidics (OM) is a vast domain encompassing different types of capillary flows, such as droplet open microfluidics, paper-based, thread-based and open-channel microfluidics. The definition of OM could be: Fluid flow at the mini or micro-scale having at least a free boundary (with air or vapor) other than an advancing meniscus. The domains where OM is currently used are space science (space plumbing), materials (polymers) microelectronics, and biology and biotechnology. In these two last domains, open structures have the advantage of cheap fabrication and easy access to the fluid. In this presentation, we focus on open-channel geometry. The geometrical conditions for spontaneous capillary flow will be presented first, using the generalized Cassie angle. Then the dynamics of these flows will be analyzed, based on the concept of average friction length. It will be shown how change of channel cross sections affects the dynamics of the flow. Extending the analysis to the flow in open networks and capillary trees, it is demonstrated that the Lucas-Washburn law must be adapted to take into account complex geometries. The case of capillary trees is especially interesting since it gives insight on capillary pumping. Finally, the flow regimes in two-phase open-capillary flows will be presented.