Deviations of Electroosmotic Fluidic Profile from Electric Double Layer Theory

The plug-like fluidic profile is one of most advantages of electroosmotic flow, which influences the reproducibility, sensitivity and separation efficiency of the microfluidic devices. Electroosmotic flow in microchannels with hydraulic diameters of less than 20 microns are investigated experimentally and qualitatively compared with prediction in electric double layer (EDL) theory. Fluidic profiles are obtained using caged-dye based technique with a high degree of resolution near the channel walls. The experimental results indicate the existence of transition zones, which is characterized by a drastic transition in velocity profile as a matching zone between the channel wall and the middle steady flow. The width scale of the transition layer was found to be the same magnitude of hydraulic diameter and much larger than the prediction in EDL theory, which is correlated with the zeta potential and length ratio of Debye length to channel´s hydraulic diameter, while the middle profile is influenced by pressure force and the viscidity force. The experiments indicate that the deviations from plug-like velocity profile can be avoided by the reduction of pressure gradient and the channel´s dimensional size