title: Understanding the onset of oscillatory swimming in microchannels.
abstract: Self-propelled colloids (swimmers) in confining geometries follow trajectories determined by hydrodynamic interactions with the bounding surfaces. However, typically these interactions are ignored or truncated to the lowest order. We demonstrate that higher-order hydrodynamic moments cause rod-like swimmers to follow oscillatory trajectories in quiescent fluid between two parallel plates, using a combination of lattice-Boltzmann simulations and far-field calculations. This behavior occurs even far from the confining walls and does not require lubrication results. We show that a swimmer's hydrodynamic quadrupole moment is crucial to the onset of the oscillatory trajectories. This insight allows us to develop a simple model for the dynamics near the channel center based on these higher hydrodynamic moments, and suggests opportunities for trajectory-based experimental characterization of swimmers' hydrodynamic properties.
authors.affiliation: Institute for Computational Physics, University of Stuttgart, Allmandring 3, 70569 Stuttgart, Germany. jgraaf@icp.uni-stuttgart.de.
authors.forename: Joost
authors.initials: J
authors.lastname: de Graaf
authors.affiliation: The Rudolf Peierls Centre for Theoretical Physics, 1 Keble Road, Oxford, OX1 3NP, UK.
authors.forename: Arnold J T M
authors.initials: AJ
authors.lastname: Mathijssen
authors.affiliation: Institute for Computational Physics, University of Stuttgart, Allmandring 3, 70569 Stuttgart, Germany. jgraaf@icp.uni-stuttgart.de.
authors.forename: Marc
authors.initials: M
authors.lastname: Fabritius
authors.affiliation: Institute for Computational Physics, University of Stuttgart, Allmandring 3, 70569 Stuttgart, Germany. jgraaf@icp.uni-stuttgart.de.
authors.forename: Henri
authors.initials: H
authors.lastname: Menke
authors.affiliation: Institute for Computational Physics, University of Stuttgart, Allmandring 3, 70569 Stuttgart, Germany. jgraaf@icp.uni-stuttgart.de.
authors.forename: Christian
authors.initials: C
authors.lastname: Holm
authors.affiliation: The Rudolf Peierls Centre for Theoretical Physics, 1 Keble Road, Oxford, OX1 3NP, UK.
authors.forename: Tyler N
authors.initials: TN
authors.lastname: Shendruk