Living clusters and crystals from low-density suspensions of active colloids.
Recent studies aimed at investigating artificial analogs of bacterial colonies have shown that low-density suspensions of self-propelled particles confined in two dimensions can assemble into finite aggregates that merge and split, but have a typical size that remains constant (living clusters). In this Letter, we address the problem of the formation of living clusters and crystals of active particles in three dimensions. We study two systems: self-propelled particles interacting via a generic attractive potential and colloids that can move toward each other as a result of active agents (e.g., by molecular motors). In both cases, fluidlike "living" clusters form. We explain this general feature in terms of the balance between active forces and regression to thermodynamic equilibrium. This balance can be quantified in terms of a dimensionless number that allows us to collapse the observed clustering behavior onto a universal curve. We also discuss how active motion affects the kinetics of crystal formation.
Deparment of Chemistry, University of Cambridge, Lensfield Road, Cambridge CB2 1EW, United Kingdom.
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Mognetti
Deparment of Chemistry, University of Cambridge, Lensfield Road, Cambridge CB2 1EW, United Kingdom and Department of Chemistry, Columbia University, 3000 Broadway, New York, New York 10027, USA.
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Sarić
Deparment of Chemistry, University of Cambridge, Lensfield Road, Cambridge CB2 1EW, United Kingdom and Institute of Physics, Humboldt Universität zu Berlin, Newtonstraße 15, 12489 Berlin, Germany.
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Angioletti-Uberti
Department of Chemistry, Columbia University, 3000 Broadway, New York, New York 10027, USA.
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Cacciuto
Departamento de Quimica Fisica I, Facultad de Ciencias Qumicas, Universidad Complutense de Madrid, 28040 Madrid, Spain.
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Valeriani
Deparment of Chemistry, University of Cambridge, Lensfield Road, Cambridge CB2 1EW, United Kingdom.
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Frenkel