Study on distribution of electrokinetic microfluid in rectangular microchannel

Electroosmotic flow is widely used as a primary method of species transport in microfluidic devices. In this work, the characteristics of electroosmotic flow in rectangular microchannels with the hydraulic diameter of 20 μm∼30 μm were investigated. Exact solutions for the velocity distribution and electroosmotic flow field are obtained by solving the complete Poisson-Boltzmann equation, describing the net charge field distribution induced by electric double layer next to a charged solid surface, and the Navier-Stokes equation, describing the hydromechanical momentum, under analytical approximation for rectangular microchannel. The simulation results of flows driven by mixed electroosmotic and pressure gradient are given. A method to extract the velocity profile from time sequence images was presented. The experiments consist of accurate observation and the behavior measurement of flow mean velocity by the digital particle images velocity (DPIV) systems. The experimental images of the electroosmotic flows profile under various value of the pressure gradient are consistent with the normalized velocity distribution. The microfluidic velocity were measured and studied as a function of hydraulic diameter ranging from 20 μm to 30 μm. The flow rate are linearly dependent on applied electric field strength. The linearity errors with standard deviation are (0.0050-0.0202) cm/s. No significant departures from continuum fluid theory have been observed ignoring the temperature changes. Thus, the behaviors of the microfluidic flow, at least down to 30 μm diameter, can be predicted by the traditional fluid theory and EDL theory. At the same time, the Joule heating gradient effect caused by the high electric strength must be considered when the channel´s dimensional size increase.