Experimental and numerical analysis of electrophoretic control of nanowires

The work in this dissertation seeks to understand the electrokinetic motion of non-spherical particles, such as nanowires, in microfluidic channels. The goals are to understand how non-spherical particles move in the channels and to determine if means exist for control of the motion, position, or orientation of the particles. The results could aid in the use of nanowires, or other non-spherical particles, in areas such as electronic device manufacturing or analysis of biological particles.;Analysis of nanowire motion under electrokinetic forces was carried out using both experimental and numerical methods. From our initial experiments we determined the average velocities of populations of nanowires. The measured velocities were used to validate theoretical predictions of electrokinetic motion. Numerical studies were used to study the motion of individual nanowires, focusing on interactions with the channel walls. When the channel diameter was decreased uniformly around the particle, the velocity of the particle decreased. However, when the particle was close to one wall, the velocity of the particle increased due to an increase in electrical field between the particle and the wall. Nonsteady numerical studies and subsequent experiments demonstrated that an interaction with the channel walls caused the nanowires to oscillate in angle and position in the channel as they moved through the channel.;Control over the position or orientation of the particles was explored through active and passive means. A 90° corner was shown to be a passive aid in aligning the nanowires. As the nanowires traveled around the corner, the nonuniform electrical and flow fields caused the nanowires to align along the center of the channel. The initial numerical studies were verified by subsequent experimental studies. To actively control the position or orientation of non-spherical particles, induced-charge electroosmosis (ICEO) was explored. ICEO uses an AC electric field to induce motion around conducting features in the channels. Numerical studies showed a wide range of control possibilities, while preliminary experiments demonstrated ICEO flows were present in the channel. Further refinement of experimental ICEO flows is ongoing through the work of Shahrzad Yazdi.;This research is consistent with previous theoretical predictions of electrokinetic motion of non-spherical particles and explores passive and active methods for motion control. The geometry of the channels was shown to passively aid in alignment of the particles. ICEO is a promising method of active positioning of the particles.