Characterization of the startup transient electrokinetic flow in rectangular channels of arbitrary dimensions, zeta potential distribution, and time‐varying pressure gradient

Abstract

The solution to the startup transient EOF in an arbitrary rectangular microchannel is derived analytically and validated experimentally. This full 2D transient solution describes the evolution of the flow through five distinct periods until reaching a final steady state. The derived analytical velocity solution is validated experimentally for different channel sizes and aspect ratios under time-varying pressure gradients. The experiments used a time resolved micro particle image velocimetry technique to calculate the startup transient velocity profiles. The measurements captured the effect of time-varying pressure gradient fields derived in the analytical solutions. This is tested by using small reservoirs at both ends of the channel which allowed a time-varying pressure gradient to develop with a time scale on the order of the transient EOF. Results showed that under these common conditions, the effect of the pressure build up in the reservoirs on the temporal development of the transient startup EOF in the channels cannot be neglected. The measurements also captured the analytical predictions for channel walls made of different materials (i.e., zeta potentials). This was tested in channels that had three PDMS and one quartz wall, resulting in a flow with an asymmetric velocity profile due to variations in the zeta potential between the walls.

Investigation of the role of template features on the electrically induced structure formation (EISF) for a faithful duplication

“…Here ε 0 is the permittivity of the free space, ε p is the relative permittivity of the polymer, and E p is the electric intensity in the polymer domain that can be deduced by Laplace equation with an assumption that the polymer is a perfect dielectric liquid, that is, no free space charge, followed as : where ε r is the relative permittivity of the air or polymer, is the electric field on the problem domain that includes E a and E p for air and polymer, respectively.…”

“…Here ε 0 is the permittivity of the free space, ε p is the relative permittivity of the polymer, and E p is the electric intensity in the polymer domain that can be deduced by Laplace equation with an assumption that the polymer is a perfect dielectric liquid, that is, no free space charge, followed as [29]:…”

Transient analysis of combined electroosmotic and pressure driven flow with multi-layer immiscible fluids in a narrow capillary

“…Focusing on electroosmotic flows, these have been studied extensively by the scientific community since many years, carrying investigations about the transport of homogeneous single-phase fluids based in electrolytic solutions both steady-state and transient-state, and using conduits formed with cylindrical shape [10][11][12], annular channels [13][14][15], parallel flat plates [16][17][18] and rectangular channels [19][20][21]; all of them, under the consideration of the Debye-Hückel approximation for the volumetric free charge density within the electric double layer.…”

Measurement of electroosmotic and electrophoretic velocities using pulsed and sinusoidal electric fields

“…Micro‐particle image velocimetry (micro‐PIV) is often used to measure the velocity of suspended tracer particles in microfluidics and it is no surprise that it has also been used to determine electrokinetic flow properties . In the high‐resolution (in space and time) transient micro‐PIV method, Yan et al.…”

“…Miller et al. derived an analytical expression for the transient startup EO flow with pressure gradient effects, from which five different periods of flow were identified until the flow reached steady‐state. Their 2D analytic solution was validated with experimental data obtained by a time‐resolved micro‐PIV relying on a high‐speed camera, for which the effect of electrophoresis on the tracer particles had to be taken into consideration (the high‐speed camera allowed the measurement of the tracer particle velocity by EP while the flow was still at rest), and good agreement was found.…”