title: Sample preconcentration inside sessile droplets using electrowetting.
abstract: Electrowetting with alternate voltage (AC) creates azimuthal flow vortices inside sessile droplets. These flow vortices can be controlled by introducing pinning sites at the contact line. When the frequency of the applied AC voltage is gradually ramped from a few hundreds of hertz to a few tens of kilohertz the azimuthal flow vortices contract and move towards the contact line near the pinning site. Dispersed particles in the liquid are collected in the center of these vortices leading to an increase in the local particle concentration by up to more than one order of magnitude. We provide a qualitative explanation for symmetry of the flow patterns within the drops and discuss possible scenarios explaining the particle collection and preconcentration.
authors.affiliation: Physics of Complex Fluids, MESA + Institute, Department of Science and Technology, University of Twente, P.O. Box 217, 7500 AE Enschede, The Netherlands.
authors.forename: Dileep
authors.initials: D
authors.lastname: Mampallil
authors.affiliation: Physics of Complex Fluids, MESA + Institute, Department of Science and Technology, University of Twente, P.O. Box 217, 7500 AE Enschede, The Netherlands.
authors.forename: Dhirendra
authors.initials: D
authors.lastname: Tiwari
authors.affiliation: Physics of Complex Fluids, MESA + Institute, Department of Science and Technology, University of Twente, P.O. Box 217, 7500 AE Enschede, The Netherlands.
authors.forename: Dirk
authors.initials: D
authors.lastname: van den Ende
authors.affiliation: Physics of Complex Fluids, MESA + Institute, Department of Science and Technology, University of Twente, P.O. Box 217, 7500 AE Enschede, The Netherlands.
authors.forename: Frieder
authors.initials: F
authors.lastname: Mugele