Spontaneous propulsion of an isotropic colloid in a phase-separating environment

Abstract

The motion of active colloids is generally achieved through their anisotropy, as exemplified by Janus colloids. Recently, there was a growing interest in the propulsion of isotropic colloids, which requires some local symmetry breaking. Although several mechanisms for such propulsion were proposed, little is known about the role played by the interactions within the environment of the colloid, which can have a dramatic effect on its propulsion. Here, we propose a minimal model of an isotropic colloid in a bath of solute particles that interact with each other. These interactions lead to a spontaneous phase transition close to the colloid, to directed motion of the colloid over very long timescales and to significantly enhanced diffusion, in spite of the crowding induced by solute particles. We determine the range of parameters where this effect is observable in the model, and we propose an effective Langevin equation that accounts for it and allows one to determine the different contributions at stake in self-propulsion and enhanced diffusion.

Passive Janus particles are self-propelled in active nematics

“…An alternative route is to immerse a passive object into an out-of-equilibrium system, extract work out of the environment [16][17][18], and transform it into a driving force [19][20][21][22][23][24][25]. In previous work, passive particles were suspended into motile bacterial baths [26][27][28][29].…”