Sedimentation and Effective Temperature of Active Colloidal Suspensions

Abstract

In this paper, we investigate experimentally the non-equilibrium steady state of an active colloidal suspension under gravity field. The active particles are made of chemically powered colloids, showing self propulsion in the presence of an added fuel, here hydrogen peroxide. The active suspension is studied in a dedicated microfluidic device, made of permeable gel microstructures. Both the microdynamics of individual colloids and the global stationary state of the suspension under gravity -density profiles, number fluctuations -are measured with optical microscopy. This allows to connect the sedimentation length to the individual self-propelled dynamics, suggesting that in the present dilute regime the active colloids behave as 'hot' particles. Our work is a first step in the experimental exploration of the out-of-equilibrium properties of artificial active systems.

Hydrodynamic simulations of self-phoretic microswimmers

“…This means that both times are also well-separated in the simulations, and that temperature profile around the swimmer is almost time-independent. D. Self-diffusiophoretic Janus colloid A colloidal particle with a well-defined part of its surface with catalytic properties can display self-propelled motion [1,3,13,14,51]. Such functional or catalytic part of the Janus particle catalyzes a chemical reaction, which creates a surrounding concentration gradient of the solvent components involved in the reaction, which typically have different interactions with the colloid.…”

“…Self-phoretic effects have shown to be an effective and promising strategy to design such artificial microswimmers [3-5, 7, 10-12], where the microswimmers are driven by gradient fields locally produced by swimmers themselves in the surrounding solvent. In particular, the collective behavior of a suspension of selfdiffusiophoretic swimmers has recently been studied in experiments [13][14][15][16].…”

Dynamics of self-propelled particles under strong confinement

“…Experiments have begun to achieve the extraordinary capabilities and emergent properties of these biological systems in nonliving active fluids of self-propelled particles, consisting of chemically [7][8][9][10][11][12] or electrically [13] propelled colloids, or monolayers of vibrated granular particles [14][15][16].…”

Sequential Tasks Performed by Catalytic Pumps for Colloidal Crystallization

“…These systems, which work far from equilibrium driven by a constant input of energy, exhibit various interesting and surprising phenomena such as collective dynamics, complex self-organization, and the emergence of large-scale coherent structures [1][2][3][4][5][6][7][8][9][10][11][12]. Biology provides a wealth of archetypes of active systems that consume chemical energy to selforganize into complex structures and to perform different collective tasks.…”

“…Artificial swimmers such as self-propelled active colloids and catalytic Janus particles also provide nice examples of collective motility, swarming and dynamic self-assembly [1,3,5,6,[8][9][10][11][30][31][32][33][34][35][36][37][38][39][40][41][42][43][44]. Microfabricated catalytic pumps can be used to manipulate particles in solution and to form crystals of colloids [45][46][47][48][49][50].…”