title: Characterization of azimuthal and radial velocity fields induced by rotors in flows with a low Reynolds number.
abstract: We theoretically and experimentally investigate the flow field that emerges from a rodlike microrotor rotating about its center in a nonaxisymmetric manner. A simple theoretical model is proposed that uses a superposition of two rotlets as a fundamental solution to the Stokes equation. The predictions of this model are compared to measurements of the azimuthal and radial microfluidic velocity field components that are induced by a rotor composed of fused microscopic spheres. The rotor is driven magnetically and the fluid flow is measured with the help of a probe particle fixed by an optical tweezer. We find considerable deviations of the mere azimuthal flow pattern induced by a single rotating sphere as it has been reported by Di Leonardo et al. [Phys. Rev. Lett. 96, 134502 (2006)]. Notably, the presence of a radial velocity component that manifests itself by an oscillation of the probe particle with twice the rotor frequency is observed. These findings open up a way to discuss possible radial transport in microfluidic devices.
authors.affiliation: Applied Laser Technologies, Ruhr-Universität Bochum, Universitätsstraße 150, 44801 Bochum, Germany.
authors.forename: J
authors.initials: J
authors.lastname: Köhler
authors.affiliation: Insitut für Theoretische Physik I, Ruhr-Universität Bochum, Universitätsstraße 150, 44801 Bochum, Germany.
authors.forename: J
authors.initials: J
authors.lastname: Friedrich
authors.affiliation: Applied Laser Technologies, Ruhr-Universität Bochum, Universitätsstraße 150, 44801 Bochum, Germany.
authors.forename: A
authors.initials: A
authors.lastname: Ostendorf
authors.affiliation: Applied Laser Technologies, Ruhr-Universität Bochum, Universitätsstraße 150, 44801 Bochum, Germany.
authors.forename: E L
authors.initials: EL
authors.lastname: Gurevich