Nonequilibrium equation of state in suspensions of active colloids

By F. Ginot, Isaac Theurkauff, D. Levis, Christophe Ybert, L. Bocquet, Ludovic Berthier, Cécile Cottin-Bizonne. 2014

174 citations recorded by the source corpus.

Active colloids constitute a novel class of materials composed of colloidal-scale particles locally converting chemical energy into motility, mimicking micro-organisms. Evolving far from equilibrium, these systems display structural organizations and dynamical properties distinct from thermalized colloidal assemblies. Harvesting the potential of this new class of systems requires the development of a conceptual framework to describe these intrinsically nonequilibrium systems. We use sedimentation experiments to probe the nonequilibrium equation of state of a bidimensional assembly of active Janus microspheres, and conduct computer simulations of a model of self-propelled hard disks. Self-propulsion profoundly affects the equation of state, but these changes can be rationalized using equilibrium concepts. We show that active colloids behave, in the dilute limit, as an ideal gas with an activity-dependent effective temperature. At finite density, increasing the activity is similar to increasing adhesion between equilibrium particles. We quantify this effective adhesion and obtain a unique scaling law relating activity and effective adhesion in both experiments and simulations. Our results provide a new and efficient way to understand the emergence of novel phases of matter in active colloidal suspensions.

Subfields: Computational Mechanics, Condensed Matter Physics, Statistical and Nonlinear Physics

View Paper: https://www.semanticscholar.org/paper/d75b0aa6b8b3d2de0175a8a17f1ec04cc6258abb

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Citations in the corpus

Pressure is not a state function for generic active fluids (2014, background): “Alternatively, when describing the dynamics of such active fluids at larger scales, some authors have introduced a bulk stress tensor and defined pressure as its trace [3, 16–18], leading to recent experimental measurements [19].”
Active Particles in Complex and Crowded Environments (2016, methodology): “These qualitative considerations have in fact been confirmed by experiments where one observes the formation of clusters at intermediate particle densities (Ginot et al., 2015; Theurkauff et al., 2012) (see also the theoretical work by Pohl and Stark (2014, 2015)).”
Minimal model of active colloids highlights the role of mechanical interactions in controlling the emergent behavior of active matter (2015, methodology): “arp increase of the pressure associated with the transition to a glassy or solid state, as in passive systems. The pressure of active Janus colloids was recently measured in sedimentation experiments [30], conﬁrming the prediction of the simulations (see Fig. 3(b)). These experiments also conﬁrmed t”
Entropy production in field theories without time reversal symmetry: Quantifying the non-equilibrium character of active matter (2016, background): “[17] Félix Ginot, Isaac Theurkauff, Demian Levis, Christophe Ybert, Lydéric Bocquet, Ludovic Berthier, and Cécile Cottin-Bizonne, “Nonequilibrium equation of state in suspensions of active colloids,” Physical Review X 5, 011004 (2015).”
Assembly and phase transitions of colloidal crystals (2016, background): “Current active-particle studies mainly focus on low-density 2D gases and small crystallites [111], whereas dense [112] and 3D active systems are desirable for phase-transition studies in the future.”