title: Artificial rheotaxis.
abstract: Motility is a basic feature of living microorganisms, and how it works is often determined by environmental cues. Recent efforts have focused on developing artificial systems that can mimic microorganisms, in particular their self-propulsion. We report on the design and characterization of synthetic self-propelled particles that migrate upstream, known as positive rheotaxis. This phenomenon results from a purely physical mechanism involving the interplay between the polarity of the particles and their alignment by a viscous torque. We show quantitative agreement between experimental data and a simple model of an overdamped Brownian pendulum. The model notably predicts the existence of a stagnation point in a diverging flow. We take advantage of this property to demonstrate that our active particles can sense and predictably organize in an imposed flow. Our colloidal system represents an important step toward the realization of biomimetic microsystems with the ability to sense and respond to environmental changes.
authors.affiliation: Department of Physics, New York University, New York, NY 10003, USA. ; Department of Physics, University of California, San Diego, La Jolla, CA 92093, USA.
authors.forename: Jérémie
authors.initials: J
authors.lastname: Palacci
authors.affiliation: Department of Chemistry, New York University, New York, NY 10003, USA.
authors.forename: Stefano
authors.initials: S
authors.lastname: Sacanna
authors.affiliation: Département de Physique, Ecole Normale Supérieure de Lyon, 69007 Lyon, France.
authors.forename: Anaïs
authors.initials: A
authors.lastname: Abramian
authors.affiliation: Center for Neural Science, New York University, New York, NY 10003, USA.
authors.forename: Jérémie
authors.initials: J
authors.lastname: Barral
authors.affiliation: School of Materials Science and Engineering, College of Engineering, Georgia Institute of Technology, Atlanta, GA 30332, USA.
authors.forename: Kasey
authors.initials: K
authors.lastname: Hanson
authors.affiliation: Department of Physics, New York University, New York, NY 10003, USA.
authors.forename: Alexander Y
authors.initials: AY
authors.lastname: Grosberg
authors.affiliation: Department of Physics, New York University, New York, NY 10003, USA.
authors.forename: David J
authors.initials: DJ
authors.lastname: Pine
authors.affiliation: Department of Physics, New York University, New York, NY 10003, USA.
authors.forename: Paul M
authors.initials: PM
authors.lastname: Chaikin
keywords: active colloids; biomimetism; non-equilibrium physics