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Alternating Current Electro-Osmotic Pumping at Asymmetrically Metallized Porous MembranesJasmin Beharic , Yehya M. Senousy , Cindy K. HarnettDepartment of Electrical and Computer Engineering, University of Louisville, Louisville, KY.

The purpose of this research is to investigate ICEO in a flow through formatAsymmetrically metallized membrane can act as an AC microfluidic pump because of induced charge electroosmosis (ICEO)Investigate the limitation of the membrane pumps Applications : bubble freelow voltage higher pressures

Theory Polarized Obstacle in a flow channel Use Membrane to create Asymmetry

Figure: (a) Induced-charge electroosmosis (ICEO) around a polarized metal obstacle in an electrolyte [3]. Ionsrearrange in response to the surface charge induced on the metal, and the ions drift in the external electric field,producing a quadrupolar flow pattern (circle). With asymmetry (triangle), net flow is possible. Electric field reversaldoes not change the flow direction, meaning that an AC field can drive unidirectional flows. (b) The proposed poregeometry will apply ICEO to a flow-through structure.

Previous Work

Previous work on planar devicesMetalized insulators

Figure : Images taken from our previous work [4] with flow in the plane of the page. (a) Fluorescent tracer beads moving around a polarized circular pillar are turned into flow streamlines (b) using particle image velocimetry. (c) Asymmetric metal-coated triangular pillars (channel width 200 microns and depths 50-300 microns), (d), their simulated loading, and (e) continuous mixing of two flowing solutions in a transverse AC electric field by both ICEO and diffusion.

Simulations Maxwell EM solver: Solve for voltage on insulating pore using Laplace solver, with DC voltage applied to top and bottom of domainLocal zeta potential is the negative of this screened voltage plus the area-averaged voltage over the metallized surface [1]

1. Wu, Zhemin, and Dongqing Li. "Mixing and flow regulating by induced-charge electrokinetic flow in a microchannel with a pair of conducting triangle hurdles." Microfluidics and nanofluidics 5.1 (2008): 65-76.

The local surface velocity comes from Helmholtz-Smoluchowski , valid for zeta potential < ~ 50 mV

+1VEM simulation domain: A wedge-shaped piece of the axisymmetric water-filled pore0V

Simulations ANSYS Fluent: Use the wall surface velocities to set boundary conditionsSet the flow rate at the simulation domain boundary (below: flow rate=0)

FabricationSU-8 Large pores are needed for ImagingTrack etch MembraneSmaller pore size needed to get readable pressure

SU-8 Membrane Bare Si WaferSpin Styrene/Toluene Release Layer Spin Su-8Perform lithography Dissolve styrene in toluene to release membrane from waferPlace membrane on support Sputter Au on membrane top and sidewallsTrack etch Membrane

Place membrane on support Sputter Au on membrane top and sidewalls

Optical Flow CaptureITO slide and Pt wire used as electrodesMembrane sandwiched

Pressure data collectionPores open after sputtering process Au present on the pore side wallsSample pressure out put profile

Figure: A) Sample Pressure Vs. Time plot B) SEM Image of post sputtering track etched membrane C) Sidewall view of track etched membranes

Testing Device Laser cut acrylic membrane holder Membrane sandwiched

Reservoir MembraneMembrane support Electrode

Experimental setupVoltage applied across inlet and outlet tubesPressure data collected using differential pressure sensor

Flow direction depends on geometry, not sign of applied voltageReversing Electrode side does not reverse the flow directionFlow direction maintained toward metallized sideWith an AC source, this experiment checks for any DC component

Pressure increases with increasing applied voltageVarying voltage 120 V90 V60 V30 VSaturation is reached after 120V

RtR1RmR1

Pressure increases with decreased pore diameter .2um Clogged pore

1um Reduced Performance

.4 um Optimal Performance

Device Behavior depends on having metalControl Device Non-metalized pore No membrane

Conclusions

AC microfluidic pump 400 Pa pressures can be achieved with a single membraneDetermined optimal operating parameters 30V to 120V 400Hz to 1kHz .4um to 1umFuture Goals Reducing Membrane sizeSelf assembled membranes Electro-less plating ApplicationsMicrofluidics Soft RoboticsBio Sensing projects

ENDSpecial thanks:Williams groupMicro/Nano Technology Center University of Louisville

Founding source:This material is based upon work supported by the National Science Foundation under Grant No. 1355438