| dc.description.abstract | Inspired by swarming motion of living organisms in nature, active particles use the stored energy in the environment to initiate self-propulsion. Successful use of active particles in different applications, including cargo transport and drug delivery, relies on their capacity to travel in predefined directions. Despite recent advances, role of polarizability in effective steering of particles under AC field has not been investigated. In this dissertation, the goal is to understand how polarizability manifests itself in the self-propulsion of particles. Metallodielectric Janus particles (JPs) serve as an effective model system for investigating active motion and collective dynamics under AC fields. Particles were fabricated by depositing sequential layers of titanium and silica on a dielectric (PS or Silica) core. Electrorotation and electroorientation measurements, along with a Poisson–Boltzmann–Nernst–Planck model in COMSOL Multiphysics, revealed two characteristic relaxation times for the polarization of JPs. At lower frequencies (below 10kHz), relaxation is attributed to the charging of an induced double layer at the particle–electrolyte interface, whereas at higher frequencies (~1MHz), the relaxation is due to the classical Maxwell–Wagner interfacial polarization. We observed that the spectra for propulsion velocity exhibited features (amplitude and transition frequencies) that closely aligned with the polarizability spectra. The insights gained from our numerical simulations prompt an expansion of our research into multiphase systems where we explore selective dynamics occurring around the air/water interface. This system allows for low-frequency attainment of rotational, translational, and interplanar motions by adjusting particle concentration and external field frequency, while at high frequencies, the particles undergo assembly at the interface. Findings in this dissertation provide a framework for designing colloids with targeted dynamical properties for the transport of cargo or microrobots. Moreover, the results can help link the complex emerging collective behavior driven by electric fields to the properties of individual particles. | |
