Sensors and Actuators B, 2003: Increasing the Performance of HighPressure, HighEfficiency Electrokinetic Micropumps Using Zwitterionic Solute Additives
Caption:
Reichmuth DS, Chirica GS, Kirby BJ, Increasing the Performance of HighPressure, HighEfficiency Electrokinetic Micropumps Using Zwitterionic Solute Additives, Sensors and Actuators BChemical, 92:3743 (2003). doi pdf
Abstract:
A zwitterionic additive is used to improve the performance of electrokinetic micropumps (EK pumps), which use voltage applied across a porous matrix to generate electroosmotic pressure and flow in microfluidic systems. Modeling of EK pump systems predicts that the additive, trimethylammoniopropane sulfonate (TMAPS), will result in up to a 3.3fold increase in pumping efficiency and up to a 2.5fold increase in the generated pressure. These predictive relations comparewell with experimental results for flow, pressure and efficiency. With these improvements,
pressures up to 156 kPa/V (22 psi/V) and efficiency up to 5.6% are demonstrated. Similar improvements can be expected from a wide range of zwitterionic species that exhibit large dipole moments and positive linear dielectric increments. These improvements lead to a reduction in voltage and power requirements and will facilitate miniaturization of micrototalanalysis systems (mTAS) and microfluidically driven actuators.
Figures:


Fig. 1. EK pump operation and characterization. (a) Schematic of experimental setup. Voltage applied across a capillary packed with silica microspheres
leads to flow and pressure generation. The fluidic resistance of the output channel controls the pressure and flow rate. Pressure is measured with a transducer
and flow is measured by observation of meniscus motion through the output channel. (b) Expanded view of EK pump. Voltage gradient induces EOF from left
to right; pressure gradient induces Pouiseille flow from right to left. (c) Expanded view of pores in between microspheres. Flow pattern is a linear
superposition of solenoidal EOF from left to right and pressuredriven Poiseuille flow from right to left. doi pdf


Fig. 2. Solution viscosity as a function of TMAPS concentration. An
exponential curve fit is used to phenomenologically
fit the data. doi pdf


Fig. 3. Effect of TMAPS on maximum pressure per volt (Pmax/V),
measured at zero net mass flux. For this figure and Figs. 46, the buffer is
10 mM Tris with varying TMAPS concentrations, and results for each
pump are normalized to the value obtained for that pump without TMAPS.
The dashed line is a prediction based on water’s dielectric constant of 81
and a linear dielectric increment of 52/M. Error bars indicate the
standard deviation of the linear fit of the pressure vs. voltage curve at each
concentration. doi pdf


Fig. 4. Dielectric increment of TMAPS inferred from a
linear fit of Pmax data in over a concentration range of 02.5 M. doi pdf


Fig. 5. Effect of TMAPS on Qmax/V, measured at zero pressure. Dashed
line indicates predicted Qmax/V using experimental viscosity data and a
dielectric increment of 52/M. Error bars indicate
the standard deviation of the linear fit of the flow rate vs. voltage curve at
each concentration. doi pdf


Fig. 6. Efficiency as a function of TMAPS concentration. Dashed line is a
prediction Eq. (5) using experimental viscosity and conductivity data and a
dielectric increment of 52/M. Error bars indicate the
standard deviation of the measured efficiencies at various voltages for each
concentration. doi pdf
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