Tue March 16th 2010
Seminar The Implications of Nonuniform Colloidal Tracer Distributions in Microscale PIV
Minami Yoda


Interfacial effects are important in many microscale transport problems. One of the few experimental techniques that can resolve interfacial transport at these scales is evanescent wave-based, or nano-, particle-image velocimetry (PIV), which determines fluid velocities within about 500 nm of the wall from the displacements of fluorescently labeled polystyrene tracers as small as 100 nm in diameter. The wall-normal spatial resolution of nano-PIV can be further improved by multilayer nano-PIV (MnPIV), which exploits the exponentially decaying intensity of evanescent-wave illumination to obtain velocities at different distances from the fluid-solid interface within the region illuminated by evanescent waves. As predicted by classic DLVO theory, the distribution of the colloidal tracers within a particle diameter of the wall measured by MnPIV is strongly nonuniform due to repulsive electric double layer interactions and van der Waals effects.
This talk describes MnPIV studies of steady creeping Poiseuille flow through hydrophilic and hydrophobically coated fused-silica microchannels with a depth of about 30 μm. The results are in good agreement with analytical predictions once the effects of the experimentally measured nonuniform tracer distributions are accounted for, and the slip lengths are found to be zero within experimental uncertainty in almost all cases. Results from MnPIV studies of electrokinetically driven flows through 40 μm deep microchannels are also presented. Measurements of the wall-parallel Brownian diffusion coefficient are in good agreement with the Faxén relation for tracers diameters ranging from 100 to 500 nm. Measurements of the near-wall distributions of 500 nm tracers suggest that there is an additional repulsive, or lift, force present at higher electric fields, presumably due to electrophoretic effects [Yariv, Phys. Fluids 18, 031702 (2006)].
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The 10th Complex Motion in Fluids 2021
Max Planck Gesellschaft
Centre for Scientific Computing