Osmotically driven flows in microchannels separated by a semipermeable membrane

Osmotically driven flows in microchannels are studied experimentally and theoretically. The propagation of the front of sugar solutions has been measured using dye and particle tracking in $200~\mu$m wide and 50, 100, and 200~$\mu$m high polymer-based microchannels. Each of these microchannels was separated by a semipermeable membrane from a reservoir containing pure water. We have also established a theoretical model of this system. In the limit of low axial flow resistance, our model predicts the propagation speed of the sugar front as a function of sugar concentration and channel geometry. The theoretical predictions agree well with the measurements. Our motivations for studying osmotically driven flows are that they are believed to be responsible for the translocation of sugar in plants and that they can be used as the driving mechanism in micropumps with no moveable parts.\\[5mm] This work was supported by the Danish National Research Foundation, Grant No. 74.