Electricfield driven active colloids moving in complex and crowded media

Abstract

Active colloids have emerged as versatile model systems for exploring non-equilibrium physics and developing microscale transport technologies. While their behavior in simple Newtonian fluids is well understood, their dynamics in complex and crowded environments remain insufficiently explored due to challenges in controlling both propulsion and environmental conditions. In this thesis, a unified experimental framework is developed to investigate the motion of active Janus particles driven by alternating current (AC) electric fields. This approach enables independent and precise control over propulsion speed, direction, and interparticle interactions through externally tunable parameters such as field strength and frequency. Importantly, it allows simultaneous manipulation of both the active particles and their surrounding environment. The study systematically explores three classes of tunable environments: viscous polymer solutions, electrohydrodynamically assembled cluster “islands” and dense polycrystalline colloidal monolayers. In polymeric media, the interplay between propulsion and viscosity leads to distinct dynamical regimes, including trapped, jittery, and directed motion. In structured island landscapes, particle obstacle interactions give rise to collision-induced reorientation and backscattering, resembling run and tumble dynamics. In crowded monolayers, externally controlled interactions enable tuning of the structural and mechanical properties of the environment, significantly affecting particle transport and persistence. Beyond fundamental insights, the work demonstrates functional capabilities such as controlled cargo capture, transport, and release in complex media. By combining externally driven propulsion with programmable environments, this thesis establishes a versatile platform for studying active matter under realistic conditions and paves the way for applications in microrobotics, targeted delivery, and adaptive materials.