FACULTY    Martin Z. Bazant (Applied Mathematics)    Todd Thorsen (Mechanical Engineering) POSTDOC    Chien-Chih Huang (Applied Math and Mech. Eng.) PhD STUDENTS    Damian Burch (Applied Mathematics)    Mustafa Sabri Kilic (Applied Mathematics)    John Paul Urbanski (Mechanical Engineering) COLLABORATORS    Armand Ajdari (ESPCI, Paris)    Todd Squires (UCSB)    Brian Storey (Olin College)    Orlin Velev (NC State) ALUMNI    Jeremy A. Levitan (PhD Mechanical Engineering 2005)    Kevin Chu (PhD Applied Math 2005)    Yuxing Ben (Postdoc 2004-2005)    Jakub Kominiarczuk (BS Physics 2007)    Matt Fishburn, Brian Wheeler, Andrew Jones (UROP)

100 micron/sec ICEO flow around a 25 micron gold post in a polymer microchannel driven by a 300 Hz 100 V/cm electric field from an experiment by J. Levitan. (Movie available below.)

Research

Press

• Big lab on a tiny chip, by C. Q. Choi, Scientific American, October 2007, pp. 100-103.
• Fast Moving Front: Induced-charge electrokinetic phenomena, Thompson Scientific, Sept. 2007.
• Portable 'lab on a chip' could speed blood tests MIT press release, October 16, 2006.
• Micropumps create a "fluid conveyor belt", press release by the Institute for Soldier Nanotechnologies, September 20, 2006.
• Fast three-dimensional pumps for microfluidics, Microsystems Technology Laboratories Annual Report 2006.
• Induced-charge electro-osmotic pumps and mixers for portable or implantable microfluidics, MTL Annual Report 2005.
• Team Combines Modeling and Experimentation to Improve Microfluidics ISN News, February 2, 2004.

Images

Simulation of 3D ACEO flow around stepped electrodes (by Yuxing Ben). Top: the electric field in phase with the AC forcing at the optimal pumping frequency. Bottom: The time-averaged streamlines showing the "fluid conveyor belt" which allows fast pumping. [Bazant & Ben, Lab on a Chip (2006).]

SEM image of a 3D ACEO pump, consisting of a periodic array of interdigitated stepped gold microelectrodes on a glass substrate (by J.P. Urbanski). Experiments confirm an order of magnitude increase in flow rate versus standard planar ACEO pumps, but also reveal a double-peaked frequency spectrum and flow reversal, not predicted by the standard theory. With design optimization, it should be possible to reach mm/sec flows with only a few volts at kHz AC frequencies, at low power (milliWatts), which could enable portable or implantable microfluidics. [Urbanski et al., Applied Physics Letters (2006).]

Movies

• Experiments. The following movies show 0.5 micron fluorescent tracer particles in various ICEO flows, visualized with an optical microscope whose focal plane cuts through the interior of a PDMS microfluidic channel on glass. These kinds of movies are used to measure complete velocity profiles by micro-particle-image velocimetry, as described by Levitan et al. (2005). The typical applied electric fields are 100 V/cm at 300 Hz AC with slip velocities of order 100 micron/sec or more.
  • One vortex in quadrupolar ICEO flow around an electroplated gold post (20 microns tall, 150 microns in diameter).
  • Fixed-potential ICEO flow over an electroplated gold surface pattern (100 micron diameter) at 3 mm/sec.
  • (low resolution) Two ICEO vortices around 100 micron platinum wire in the experiment of Levitan et al. (2005). The movie shows the focal plane, parallel to the channel walls and perpendicular to the wire axis, at first cutting through the wire, showing converging flow, and then sweeping slowly up and away from the wire, eventually showing diverging flow, in a convection roll out of the plane.

• Simulations. Finite-element numerical simulations of electrochemical relaxation and ICEO flow around a metal cylinder in a suddenly applied uniform background electric field, modeled by the Poisson-Nernst-Planck equations and Navier-Stokes equations with electrostatic stresses, respectively. Debye length/ cylinder radius = 0.005. (Simulation by Yuxing Ben in FEMLAB.)
  • Evolution of the electric field around the metal cylinder. Notice how the bulk field lines are expelled from the double layer as it charges, although they turn sharply and always touch perpendicular to the surface, which remains an equipotential surface.
  • Evolution of the ICEO fluid velocity showing the formation of a quadrupolar Stokes flow outside the double layer, due to effective slip just outside the double layer, while maintaining the no-slip condition at the metal surface.

Slides

The slides from these public lectures are available online, subject to the copyright restrictions below.

Publications

Theoretical Papers

1. Induced-charge electro-kinetic phenomena: Theory and microfluidic applications, M. Z. Bazant and T. M. Squires, Phys. Rev. Lett. 92, art. no. 066101 (2004). (This paper triggered a Fast Moving Front of research.)
2. Induced-charge electro-osmosis, T. M. Squires and M. Z. Bazant, J. Fluid. Mech. 509, 217-252 (2004).
3. Diffuse-charge dynamics in electrochemical systems, M. Z. Bazant, K. Thornton, and A. Ajdari, Phys. Rev. E 70, 021506 (2004).
4. Breaking symmetries in induced-charge electro-osmosis, T. M. Squires and M. Z. Bazant, J. Fluid Mech. 560, 65-101 (2006).
5. Nonlinear electrochemical relaxation around conductors, K. T. Chu and M. Z. Bazant, Phys. Rev. E 74, 011501 (2006).
6. Theoretical prediction of fast 3D AC electro-osmotic pumps, M. Z. Bazant and Y. Ben, Lab on a Chip, 6, 1455-1461 (2006).
7. Steric effects in the dynamics of electrolytes at large applied voltages: I. Double-layer charging, M. S. Kilic, M. Z. Bazant, and A. Ajdari, Phys. Rev. E 75, 021502 (2007).
8. Steric effects in the dynamics of electrolytes at large applied voltages: II. Modified Nernst-Planck equations, M. S. Kilic, M. Z. Bazant, and A.Ajdari, Phys. Rev. E 75, 021503 (2007).
9. Surface conservation laws at microscopically diffuse interfaces, K. T. Chu and M. Z. Bazant, J. Colloid and Interface Science 315, 319-329 (2007).
10. Nonlinear electrokinetics at large applied voltages, M. Z. Bazant, M. S. Kilic, B. Storey, and A. Ajdari, e-print (2007).
11. Steric effects on ac electro-osmosis in dilute electrolytes, B. Storey, L. R. Edwards, M. S. Kilic, and M. Z. Bazant, Phys. Rev. E 77, 036317 (2008).
12. Design principle for improved three-dimensional ac electro-osmotic pumps, D. Burch and M. Z. Bazant, Phys. Rev. E 77, 055303(R) (2008).
13. Induced-charge electrophoresis near an insulating wall, M. S. Kilic and M. Z. Bazant.
14. Numerical studies of nonlinear kinetics in induced-charge electro-osmosis, M. M. Gregersen, M. Z. Bazant, and H. Bruus, XXII ICTAM Proceedings, Adelaide, Australia (2008).

    Experimental Papers

15. Experimental observation of induced-charge electro-osmosis around a metal wire in a microchannel, J. A. Levitan, S. Devasenathipathy, V. Studer, Y. Ben, T. Thorsen, T. M. Squires, and M. Z. Bazant, Colloids and Surfaces A 267, 122-132 (2005).
16. Fast AC electro-osmotic pumps with non-planar electrodes, J. P. Urbanski, T. Thorsen, J. A. Levitan, and M. Z. Bazant, Applied Physics Letters 89, 143508 (2006).
17. The effect of step height on the performance of AC electro-osmotic microfluidic pumps, J. P. Urbanski, J. A. Levitan, D. N. Burch, T. Thorsen, and M. Z. Bazant, Journal of Interface and Colloid Science 309, 332-341 (2007).
18. Electrolyte dependence of AC electro-osmosis, M. Z. Bazant, J. P. Urbanski, J. A. Levitan, K. Subramanian, M. S. Kilic, A. Jones, and T. Thorsen, Proceedings of 11th International Conference on Miniaturized Systems for Chemistry and Life Sciences (MicroTAS), 285-2878 (2007).
19. Experimental study of electrolyte dependence of AC electro-osmotic pumps, K. Subramanian, J. P. Urbanski, J. A. Levitan, T. Thorsen, and M. Z. Bazant, Proceedings of the International Conference on Micro, Meso, and Nanoengineering, Trivandrum, India (2007).
20. Induced-charge electrophoresis of metallo-dielectric particles, S. Gangwal, O. J. Cayre, M. Z. Bazant, and O. D. Velev, Phys. Rev. Lett. 100, 058302 (2008).
21. Flow reversal of AC electro-osmotic pumps due to steric effects, B. Storey, L. R. Edwards, M. S. Kilic, and M. Z. Bazant, to appear in Phys. Rev. E.

    Encyclopedia Articles

    The following articles by M. Z. Bazant and related definitions will appear in the Encyclopedia of Microfluidics and Nanofluidics, ed. by Dongqing Li, in press (Springer, Berlin New York, Heidelberg, 2008). Authorized draft preprints can be downloaded for personal and educational use.

22. Nonlinear electrokinetic phenomena
23. AC electro-osmotic flow
24. Electrokinetic motion of polarizable particles
25. Electrokinetic motion of heterogeneous particles

    Patents

26. Microfluidic pumps and mixers driven by induced-charge electro-osmosis, T. M. Squires and M. Z. Bazant, US Patent 7,081,189, issued July 25, 2006, filed in 2002. International Patent PCT/US02/40290. (MIT Case 9576)
27. Fabrication methods and designs for microfluidic devices exploiting induced-charge electro-osmosis, J. A. Levitan, T. Thorsen, M. Schmidt, and M. Z. Bazant, US provisional patent, filed in Oct. 2004. (MIT Case 11683).
28. Fast Induced-Charge Electro-osmotic Pumps for Microfluidics: I. Designs Exploiting Fixed-Potential ICEO, M. Z. Bazant, US Provisional patent, filed Jan 2006, (MIT Case 12056).
29. Fast Induced-Charge Electro-osmotic Pumps for Microfluidics: II. Designs with multilevel pumping surfaces, M. Z. Bazant and Y. Ben, US Provisional patent, filed Jan 2006, (MIT Case 12057).
30. Temporal modulation of electrokinetic pumps for microfluidic mixing, M. Z. Bazant and J. Levitan, provisional patent.

    Ph.D. Theses

31. J. A. Levitan,Experimental Investigation of Induced-Charge Electro-osmosis, Doctoral Thesis in Mechanical Engineering, MIT (2005).
32. K. T. Chu, Asymptotic Analysis of Extreme Electrochemical Transport, Doctoral Thesis in Applied Mathematics, MIT (2005).

Support

• National Science Foundation, Contract DMS-0707641 with the Division of Mathematical Sciences (2007-present)
• MIT Insitute for Soldier Nanotechnologies, Contract DAAD-19-02-0002 with the U.S. Army Research Office (2002-present)
• MIT-France Program, seed grant (2004)
• MIT-Spain Program, seed grant (2008)
• MIT Microsystems Technology Laboratories

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