Electrodynamics of particles in bulk fluid and on an interface

Hu, Yi

doi:https://doi.org/10.21985/n2-45gc-ss66

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Electrodynamics of particles in bulk fluid and on an interface

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The focus on this thesis is on the dynamics of colloidal particles in an applied electric field in a uniform bulk fluid and on a fluid-fluid interface. In a bulk fluid, the dynamics of an isolated particle, one pair, and a cluster of particles under an applied nonuniform electric field are modeled and simulated. The local and far-field electric field perturbation by a spherical particle trapped at a fluid-fluid interface is also studied. The electric potential is found by using the Mehler-Fock integral transform, which reduces the problem to a system of Fredholm integral equations. These equations are solved numerically and asymptotically. The force on an isolated particle is identified numerically, while the far-field interaction force between two particles is identified asymptotically. We show that, at leading order, the interaction between perfect dielectric particles is dominated by the induced dipoles and hence it is repulsive. For leaky dielectric particles the induced quadrupole can become significant and the interaction force can be either attractive or repulsive depending on material parameters. Moreover, a mathematical model to simulate the dynamics of colloidal particles on a drop interface in an applied electric field is presented. The model accounts for the electric field driven {flow} within the drop and suspending fluid, particle-particle electrostatic interaction, and the particle motion and rotation due to the induced flow and the applied electric field. A study is presented on the impact of particle concentration and electric field strength on the collective motions of the particles. In the case of non-conducting particles, we find that in the presence of Quincke rotation, the amplitude of {the undulations} of the observed equatorial particle belt increases with particle concentration but decreases with electric field strength. We also show that the wavelength of the {undulations} appears independent of the applied field strength.

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