title: Clusters, asters, and collective oscillations in chemotactic colloids.
abstract: The creation of synthetic systems that emulate the defining properties of living matter, such as motility, gradient-sensing, signaling, and replication, is a grand challenge of biomimetics. Such imitations of life crucially contain active components that transform chemical energy into directed motion. These artificial realizations of motility point in the direction of a new paradigm in engineering, through the design of emergent behavior by manipulating properties at the scale of the individual components. Catalytic colloidal swimmers are a particularly promising example of such systems. Here we present a comprehensive theoretical description of gradient-sensing of an individual swimmer, leading controllably to chemotactic or anti-chemotactic behavior, and use it to construct a framework for studying their collective behavior. We find that both the positional and the orientational degrees of freedom of the active colloids can exhibit condensation, signaling formation of clusters and asters. The kinetics of catalysis introduces a natural control parameter for the range of the interaction mediated by the diffusing chemical species. For various regimes in parameter space in the long-ranged limit our system displays precise analogs to gravitational collapse, plasma oscillations, and electrostatic screening. We present prescriptions for how to tune the surface properties of the colloids during fabrication to achieve each type of behavior.
authors.affiliation: Department of Physics, Indian Institute of Science, Bangalore 560 012, India and TIFR Centre for Interdisciplinary Sciences, 21 Brundavan Colony, Osman Sagar Road, Narsingi, Hyderabad 500 075, India.
authors.forename: Suropriya
authors.initials: S
authors.lastname: Saha
authors.affiliation: Rudolf Peierls Center for Theoretical Physics, University of Oxford, 1 Keble Road, Oxford OX1 3NP, United Kingdom.
authors.forename: Ramin
authors.initials: R
authors.lastname: Golestanian
authors.affiliation: Department of Physics, Indian Institute of Science, Bangalore 560 012, India and TIFR Centre for Interdisciplinary Sciences, 21 Brundavan Colony, Osman Sagar Road, Narsingi, Hyderabad 500 075, India.
authors.forename: Sriram
authors.initials: S
authors.lastname: Ramaswamy
mesh_terms: D040761:Biomimetic Materials / Q000737:chemistry*; D002633:Chemotaxis; D003102:Colloids / Q000737:chemistry*; D003198:Computer Simulation; D008956:Models, Chemical; D009991:Oscillometry / Q000379:methods; D044367:Phase Transition; D012212:Rheology / Q000379:methods*; D012996:Solutions / Q000737:chemistry*
chemical_list: D003102:Colloids; D012996:Solutions