Title: Contact Charge Electrophoresis
Description: In 1745 a Scotch Benedictine monk Andrew Gordon discovered Contact Charge Electrophoresis (CCEP) which remained in dormant state for centuries until gaining renewed prominence in the field of particle manipulation and actuation. Contact Charge Electrophoresis (CCEP) refers to the continuous to and fro motion of a conductive object between two electrodes subject to an applied voltage. The continuous motion of the conductive particle and the low power requirement provide an attractive alternative to traditional methods for particle manipulation techniques such as dielectrophoresis. Recent efforts to understand and apply CCEP have focused on the motion of single particles and we present dynamics of multiple conductive particles dispersed in non-conducting media that utilize CCEP to perform tasks like pumping and cargo transport operations as well as multiparticle clusters capable of tailored trajectories. Chapters 1 provides motivation for this work and background on CCEP. Providing brief details on development of microfluidic devices and modeling that are covered in more details in subsequent chapters.

It also focuses on the historical aspect of CCEP, relevant background, mechanism, physics, application strategies in literature, strategies developed for single particle systems and possible extension to multiparticle systems. Chapters 2 and 3 talk about the dynamics and modeling of multiple conductive particles both in dispersion and aggregates/clusters powered by CCEP. In Chapter 2, we propose a new hybrid approach based on image-based method proposed earlier by Bonnecaze[18] for modeling CCEP. It covers challenges to modeling a multiple particle system in confinement, dynamics of chain formation and dynamics of cluster comprising conductive and non-conductive particles between two electrodes. While Chapter 3 focuses on details of methods and techniques used in development of the simulation for dispersion of conductive particles in confinement. Here we also illustrate variation of conductivity for complete range of electrode separation with varying volume fraction. Chapter 4 expands on multiple particle CCEP and shows that when we physically constrain particle trajectories to parallel tracks between the electrodes, the traveling waves of mechanical actuation can be realized in linear arrays of electromechanical oscillators that move and interact via electrostatic forces.

Conductive spheres oscillate between biased electrodes through cycles of contact charging and electrostatic actuation. The combination of repulsive interactions among the particles and spatial gradients in their natural frequencies lead to phase locked states characterized by gradients in the oscillation phase. The frequency and wavelength of these traveling waves can be specified independently by varying the applied voltage and the electrode separation. We demonstrate how traveling wave synchronization can enable the directed transport of material cargo. Our results suggests that simple energy inputs can power complex patterns of mechanical actuation with potential opportunities for soft robotics and colloidal machines. Chapter 5 systematically investigate the dynamics of cluster comprising multiple spherical conductive particles driven via contact charge electrophoresis (CCEP). We are specifically interested in understanding dynamics of closed packed cluster of particles with both conductive and non-conductive particles in three dimensions(3D).

Finally, Chapter 6 summarizes new ideas and proposes possible applications for multiple particle Contact charge electrophoresis motivated by this dissertation.