Electroosmotic Capillary Flow with Nonuniform Zeta Potential

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Abstract
The present work is an analytical and experimental study of electroosmotic flow (EOF) in cylindrical capillaries with nonuniform wall surface charge (ζ-potential) distributions. In particular, this study investigates perturbations of electroosmotic flow in open capillaries that are due to induced pressure gradients resulting from axial variations in the wall ζ-potential. The experimental inquiry focuses on electroosmotic flow under a uniform applied field in capillaries with an EOF-suppressing polymer adsorbed onto various fractions of the total capillary length. This fractional EOF suppression was achieved by coupling capillaries with substantially different ζ-potentials. The resulting flow fields were imaged with a nonintrusive, caged-fluorescence imaging technique. Simple analytical models for the velocity field and rate of sample dispersion in capillaries with axial ζ-potential variations are presented. The resulting induced pressure gradients and the associated band-broadening effects are of particular importance to the performance of chemical and biochemical analysis systems such as capillary electrokinetic chromatography and capillary zone electrophoresis.