Equipment grant for interfacial velocimetry and 3d liquid-phase thermometry in microfluidic devices
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In terms of colloid science, these experiments have demonstrated that an electric field applied parallel to the wall creates an additional nonlinear electrokinetic force that repels near-wall (i.e., those less than 300 nm from the wall) particles of radii ranging from 0.2 um to 0.5 um. The measurements verify previous theoretical predictions of a force that scales with the square of the electric field magnitude and the square of the particle radius, albeit with a magnitude one to two orders of magnitude greater than that predicted by the theory (note that the original theory was developed for 'remote wall-sphere interactions'). In terms of fluid mechanics, this result suggests that knowledge of the near-wall particle distribution will be required to accurately measure near-wall velocity fields with particle velocimetry techniques (e.g. micro-PIV and evanescent-wave particle velocimetry). Without this knowledge, using tracers of different diameters in these techniques will give different results for the velocity field for a shear flow where there is an electric field parallel to the wall, such as combined electroosmotic and Poiseuille flow.