Seminar: Colloidal Particle Dynamics in Poiseuille and Electroosmotic Flow through Microchannels

Abstract:

Manipulating colloidal particles of radii a = O(0.1 mm–1 mm) suspended in an aqueous electrolyte solution in a microchannel flow near the channel wall so that the particles can be detected and analyzed by wall-mounted sensors, is an important technology in microfluidics applications.  These particles are, however, subject to various forces that usually drive them away from the wall.  We have recently studied the dynamics of these particles in Poiseuille flow driven by a pressure gradient Dp/L, and in electroosmotic (EO) flow driven by a voltage gradient or electric field of magnitude /E/.

Fluorescent a = 245 nm particles were visualized with evanescent-wave illumination due to the total internal reflection of a blue laser beam at the interface between the fused-silica microchannel wall and the fluid.  The evanescent waves, which have an intensity that decays exponentially with the distance from the wall, only illuminate the particles that are within about 0.5 mm of the wall. 

The dynamics of these particles, suspended in dilute aqueous solution at volume fractions f = 0.17%, were studied in Poiseuille flow at Dp/L < 1.1 Bar/m and combined Poiseuille and EO flow at  < 100 V/cm through 30 mm deep channels.  When both flows are in the same direction, the particles are strongly repelled from the wall, with a force that appears to be much greater than the sum of the forces observed in “pure” EO or “pure” Poiseuille flow.  More surprising, when the EO and Poiseuille flows are in opposite directions, the negatively charged particles are attracted to the negatively charged wall at small /E/, and self-assemble into periodic streamwise bands at larger /E/.  This talk will discuss these observations. 

About the Speaker:

Minami Yoda did her undergraduate studies at Caltech, her graduate studies at Stanford University, and was a von Humboldt and National Science Foundation postdoctoral fellow at the Technical University of Berlin in Germany.  Dr. Yoda is Associate Editor for the journal Experiments in Fluids, the former Chair of the American Nuclear Society Fusion Energy Division, and a former member of the Executive Committee of the American Physical Society Division of Fluid Dynamics.  She is a Fellow of the American Physical Society and the American Society of Mechanical Engineers.  Dr. Yoda’s current research interests include experimental fluid mechanics, optical measurement techniques, microfluidics, colloid science, Marangoni-buoyancy convection, and high heat flux plasma-facing components in magnetic fusion energy.

Hosted by Professors Shaurya Prakash and Terry Conlisk