Polarizability of particles with combined chemical and geometrical anisotropy: The case of Janus ellipsoids.

While various factors influence the polarizability of colloidal particles, the concurrent effects of chemical and geometric anisotropy have yet to be quantified. We address this gap by investigating Janus ellipsoids with aspect ratios ranging from 1.5 to 5, which serve as model systems for particles with combined anisotropy. Electrorotation measurements reveal three distinct relaxations due to concentration polarization, induced charge polarization, and the Maxwell-Wagner-O'Konski mechanism. Surface charge, particle aspect ratio, and medium conductivity govern the observed behavior, with conductivity offering the greatest experimental flexibility for tuning polarizability. Crucially, while these mechanisms are traditionally treated as distinct, our results demonstrate that concentration polarization and induced charge polarization can overlap and compete in the low frequency regime. This finding has significant implications for active matter experiments, which are frequently conducted at low frequencies. These insights provide guidance for leveraging polarization mechanisms to control separation, propulsion, and field directed assembly of anisotropic particles.