title: Bidirectional particle transport and size selective sorting of Brownian particles in a flashing spatially periodic energy landscape.
abstract: We demonstrate a size sensitive experimental scheme which enables bidirectional transport and fractionation of paramagnetic colloids in a fluid medium. It is shown that two types of magnetic colloidal particles with different sizes can be simultaneously transported in opposite directions, when deposited above a stripe-patterned ferrite garnet film subjected to a square-wave magnetic modulation. Due to their different sizes, the particles are located at distinct elevations above the surface, and they experience two different energy landscapes, generated by the modulated magnetic substrate. By combining theoretical arguments and numerical simulations, we reveal such energy landscapes, which fully explain the bidirectional transport mechanism. The proposed technique does not require pre-imposed channel geometries such as in conventional microfluidics or lab-on-a-chip systems, and permits remote control over the particle motion, speed and trajectory, by using relatively low intense magnetic fields.
authors.affiliation: Departament de Física de la Matèria Condensada, Universitat de Barcelona, Av. Diagonal 647, 08028, Barcelona, Spain. ptierno@ub.edu.
authors.forename: Fernando
authors.initials: F
authors.lastname: Martinez-Pedrero
authors.affiliation: Departament de Física de la Matèria Condensada, Universitat de Barcelona, Av. Diagonal 647, 08028, Barcelona, Spain. ptierno@ub.edu.
authors.forename: Helena
authors.initials: H
authors.lastname: Massana-Cid
authors.affiliation: Department of Physics, Humboldt-Universität zu Berlin, Newtonstr. 15, 12489 Berlin, Germany.
authors.forename: Till
authors.initials: T
authors.lastname: Ziegler
authors.affiliation: Department of Physics, The University of Oslo, P.O. Box 1048 Blindern, 0316 Oslo, Norway and Institute for Superconducting and Electronic Materials, University of Wollongong, Wollongong, New South Wales 2522, Australia.
authors.forename: Tom H
authors.initials: TH
authors.lastname: Johansen
authors.affiliation: Departament de Física de la Matèria Condensada, Universitat de Barcelona, Av. Diagonal 647, 08028, Barcelona, Spain. ptierno@ub.edu and Department of Mathematics and Computer Science, Freie Universität Berlin, Arnimallee 6, 14195, Berlin, Germany.
authors.forename: Arthur V
authors.initials: AV
authors.lastname: Straube
authors.affiliation: Departament de Física de la Matèria Condensada, Universitat de Barcelona, Av. Diagonal 647, 08028, Barcelona, Spain. ptierno@ub.edu and Institut de Nanociència i Nanotecnologia, IN2UB, Universitat de Barcelona, Av. Diagonal 647, 08028, Barcelona, Spain and Universitat de Barcelona Institute of Complex Systems (UBICS), Universitat de Barcelona, Barcelona, Spain.
authors.forename: Pietro
authors.initials: P
authors.lastname: Tierno