Polarization-Selective Dynamic Coupling: Electrorotation-Orbital Motion of Twin Colloids in Rotating Fields

This study investigates dynamic electrohydrodynamic (EHD) interactions between two identical colloidal microspheres in rotating electric fields using a fully coupled three-dimensional transient model. Long-range dielectrophoretic (DEP) attraction drives radial convergence; upon near-contact, tangential EHD sliding further induces asynchronous co-field orbital revolution. Crucially, individual electrorotation (ER) not only retains its original direction but also maintains a stable rate—with the rate deviating by <5% from that of isolated particles, matching single-particle behavior. High-frequency DEP force polarity reversal establishes stable noncontact equilibria via short-range repulsion. Spectral analyses reveal collective dynamics (radial mobility, orbital motion) stem from rotating electric field-mediated gap modulation rather than altered particle polarization. This dynamic decoupling—governed by the Kramers–Kronig relationship between real (radial DEP) and imaginary (rotational ER) components of polarizability—enables independent positional and rotational control, opening new avenues for noncontact colloidal manipulation in microfluidic mixers and dynamically reconfigurable active matter systems, where conventional DEP-based approaches are limited by coupled dynamics.