Active particle dynamics in uniform and patterned electroosmotic flows

Abstract

We investigate the dynamics of self-propelled spheroidal particles in electroosmotic channel flows generated by uniform, patterned, and combined zeta-potential distributions. The coupling between self-propulsion, particle shape, and electroosmotic advection gives rise to distinct regimes of confinement and transport. For a uniform zeta potential, the dynamics reduce to a two-dimensional system in cross-stream position and orientation. We show that this system possesses a non-canonical Hamiltonian structure, allowing its phase-space organization to be characterized analytically. For spherical particles, the dynamics admit a nonlinear-pendulum description, yielding the characteristic oscillation frequency and extent of the confined region. The oscillation frequency depends non-monotonically on electrostatic screening and reaches a maximum at an intermediate Debye parameter. Spatially patterned zeta potentials reorganize the dynamics by generating counter-rotating vortices and coupling streamwise position, cross-stream position, and particle orientation. Numerical simulations and dynamical-systems analysis reveal regimes of single-cell confinement and cross-cell migration, controlled by particle shape and electrostatic screening. When uniform and patterned components coexist, mean electroosmotic advection competes with vortex-induced recirculation, producing transport sensitive to particle shape and initial conditions. Together, these results connect Hamiltonian phase-space dynamics in uniform electroosmotic flow to vortex-mediated trapping and transport in patterned flows, highlighting the potential of surface electrostatic patterning to control particle motion without altering channel geometry.