Interacting self-phoretic particles on a ring

Abstract

We study the spontaneous motion and collective dynamics of self-phoretic particles on a ring. The particles act as localized sources of a chemical field, with particle-dependent source strengths, and respond to gradients of this field through particle-dependent phoretic mobilities. The chemical field undergoes diffusion and evaporation. For a single particle, we derive the exact threshold for spontaneous propulsion and establish the emergence of stable constant-velocity states near onset through a supercritical pitchfork bifurcation. We then consider an active source coupled to a non-emitting tracer and determine the conditions for slipping and stable phase-locked motion. For two mutually coupled sources, the stationary antipodal configuration can lose stability through either a pitchfork or a Hopf bifurcation, depending on the relative source strengths and phoretic mobilities. We determine the competing instability thresholds and compare them with direct numerical simulations of the coupled particle-field equations. Beyond onset, the resulting translating and oscillatory states provide qualitative counterparts to modes of motion observed experimentally for camphor disks in annular water channels. These results connect the onset of individual propulsion, tracer entrainment, and collective motion within a common analytically tractable framework.

arXiv comment56 pages