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Microfluidic mixing via transverse electrokinetic effects in a planar microchannel

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Abstract

A new micromixer incorporating integrated electrodes deposited on the bottom surface of a glass/PDMS microchannel is used to induce a localized, perpendicular electric field within pressure driven axial flow. The presence of the electric field drives electro-osmotic flow in the transverse direction along the channel walls, creating helical motion that serves to mix the fluid. A numerical model is used to describe the three-dimensional flow field, where characterization is performed via particle tracking of passive tracer particles, and the conditional entropy (S lc) is utilized to approximate the extent of mixing along cross-sectional planes. The geometrical parameters and operating conditions of the numerical model are used to fabricate an experimental device, and fluorescence microscopy measurements are used to verify mixing of rhodamine B across the width of the microchannel for a wide range of fluid flow rates. The results demonstrate that under certain operating conditions and selective placement of the electrode gaps along the width of the microchannel, efficient mixing can be achieved within 6 mm of the inlet.

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Notes

  1. Animations displaying the on/off operation of the mixing procedure can be found at http://navier.engr.colostate.edu/eof/.

  2. Animations of fluorescent microsphere entrapment within the primary recirculation region can be found at http://navier.engr.colostate.edu/eof/.

Abbreviations

L mix :

characteristic length for mixing

T mix :

characteristic time for mixing

ϕ :

externally applied potential

λ d :

debye length

ε :

dielectric constant of the fluid

ε o :

permittivity of vacuum

ζ :

zeta-potential

\( \ifmmode\expandafter\vec\else\expandafter\vec\fi{E} \) :

electric field vector

p :

pressure

μ :

viscosity

\( \ifmmode\expandafter\vec\else\expandafter\vec\fi{u} \) :

linear velocity

φ :

stream function

l e :

axial length of the electrode

w g :

width of the electrode gap

w c :

center position of the electrode gap

t comp :

computational time for particle advection

t n :

average computational time for advection between planes

S lc :

conditional mixing entropy

p j :

probability that a particle is in bin j irrespective of species

p c,j :

probability that a particle is of the type c whose position is in bin j

δ a :

adjusted extent of mixing

I i :

fluorescent intensity at pixel i during active mixing

I i,o :

fluorescent intensity at pixel i if no active mixing occurs

N :

total number of pixels across the width of the micro-channel

w :

width of micro-channel

h :

height of micro-channel

n :

total number of electrode cycles

F :

mixing effectiveness

M :

number of bins used to discretize channel cross-sections

w b :

width of bin

l i :

axial position at the start of the i-th electrode cycle

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Acknowledgments

This work was supported by NIH grant number EB00726.

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Authors and Affiliations

  1. Department of Chemical and Biological Engineering, Colorado State University, Fort Collins, CO, 80523, USA

    N. Scott Lynn & David S. Dandy

  2. Department of Chemistry, Colorado State University, Fort Collins, CO, 80523, USA

    Charles S. Henry

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  1. N. Scott Lynn
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Correspondence to David S. Dandy.

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Lynn, N.S., Henry, C.S. & Dandy, D.S. Microfluidic mixing via transverse electrokinetic effects in a planar microchannel. Microfluid Nanofluid 5, 493–505 (2008). https://doi.org/10.1007/s10404-008-0258-8

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  • DOI: https://doi.org/10.1007/s10404-008-0258-8

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