Electricfield driven active colloids moving in complex and crowded media
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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.