Schematic diagram of experimental setup for current monitoring method.
Current-time curve for displacement flow of 0.2 mM and 1 mM KCl solutions in glass micro-capillary.
Displacement time for 1 mM KCl with (a) 0.2 mM, (b) 0.5 mM, (c) 0.7 mM, and (d) 0.95 mM KCl for flows in both directions in glass micro-capillary with diameter of 100 μm and length of 8 cm under applied voltage of 1000 V. Error bars indicate the standard deviations.
Percentage time difference between displacement time in both directions for KCl solution with various percentage of concentration differences at various (a) voltages (with micro-capillary length of 8 cm and diameter of 100 μm), (b) micro-capillary diameters (length was fixed at 8 cm), and (c) micro-capillary lengths (diameter was fixed at 100 μm).
(a) Displacement time in PDMS microchannel with KCl solutions of various percentage concentration differences under applied voltage of 330 V over channel length of 5.5 cm and (b) comparison between percentage time difference for PDMS channel and glass micro-capillary (6 cm) at various concentration differences.
Simulation domain and coordinate system for axisymmetric analysis.
Flowchart of numerical solving process.
Numerical results showing (a) flow rate and (b) displacement of fluid interface in the displacement flow of 0.01 mM and 0.002 mM solutions. Single fluid flows for each of the two solutions are shown for reference.
Comparison between experimental and numerical results for displacement flow of two solutions with 80% concentration difference. Currents are normalized with maximum and minimum currents. Time is normalized with the time for the descending curve to reach a steady current.
Positive and negative ion distributions x = 0.8 × 10−4 m for the flow of (a) 0.002 mM displacing 0.01 mM and (b) 0.01 mM displacing 0.002 mM. Full curves represent negative ion and dashed curves represent positive ion.
Snapshots of velocity vector plot for flow of (a) 0.002 mM displacing 0.01 mM and (b) 0.01 mM displacing 0.002 mM. Numerical results show that velocity profiles in two fluid displacement flow deviate from the plug-like profile of a typical electroosmotic flow.
Comparison of negative ion distributions between both flow directions at bulk concentration of 0.004 mM, 0.006 mM and 0.008 mM at x = 0.8 × 10−4 m. Full curves represent the case of high concentration displacing low concentration and dashed curves represent the case of low concentration displacing high concentration.
t-score for displacement time of various solutions pairs at 3 voltages applied in glass micro-capillary.
Symbols and values of parameters in numerical models.
Summary of boundary conditions for steady state numerical model for single fluid electroosmotic flow.
Changes in inlet boundary conditions for two-fluid displacement flow (R= concentration ratio between two solutions).
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