Download 2. Patterned Microfluidic Channel

Alternating Zeta-Potential Pattern to
Eliminate Electro-Osmotic Flow
Caspar Schreuer, T. Brans, S. Vandewiele, F. Strubbe,
K. Neyts and Filip Beunis
Department of Electronics and Information Systems, Ghent University
Center for Nano- and Biophotonics (NB-Photonics), Ghent University
Email: [email protected]
http://lcp.elis.ugent.be
Introduction
1. Electro-osmosis
The electrophoretic mobility is a measure for the mobility and the
stability of particles in a colloidal suspension. It is defined as the
ratio of the particle velocity and the applied electric field:
A glass substrate has a finite surface charge at the glass-liquid
interface. This surface charge attracts an excess of mobile ions of
opposite polarity near the surface. When an electric field is
applied parallel to this interface, the Coulomb force induces the
ions to move. This effect causes a parabolic fluid flow across the
channel.
𝑣
𝜇𝑒 =
𝐸
In polar liquids, measurements of the electrophoretic mobility are
complicated by a fluid flow, which superimposes the flow velocity
on the particle velocity, effectively limiting the measurement
accuracy. This flow is called electro-osmotic flow.
Surface
charge
This poster discusses a novel method that aims to eliminate
electro-osmosis in the bulk of a microfluidic channel.
Mobile
ions
E
2. Patterned Microfluidic Channel
In order to eliminate the electro-osmotic flow, a pattern can be
printed onto the surface of the channel. This pattern consists of
parallel stripes that are transversal to the electric field. The material
of the imprinted stripes is chosen to have a zeta-potential with the
opposite polarity of the glass substrate.
Electro-osmosis in a closed channel
3. Simulation results
A vertical cross section of the flow in the channel reveals that the
patterned channel reduces the velocity by two orders of magnitude
and has a uniform profile in the center. The channel has been
optimized by varying the relative thicknesses of the stripes.
200µm
Flow (mm/s)
10-1
200µm
Glass, ζ = -0.028V
Al2O3, ζ = 0.06V
10-2
10-3
10-4
10-5
0
40
80
120
160
Distance from the bottom substrate (µm)
200
Simulation of the channel, applied DC voltage 10V,
(black) regular channel, (dotted) patterned channel
Patterned microfluidic channel, proportions are not to scale
Each stripe will build up a mobile ion layer with the opposite
polarity with respect to its neighbors. In the presence of an electric
field, these mobile ion layers will flow against each other. This gives
rise to vortex-like flow near the boundaries, but when the channel
is sufficiently thick (thickness > 10 x pattern period), no net flow is
coupled to the bulk of the channel.
11th International Symposium on Electrokinetic Phenomena
Conclusions and prospects
The simulation reveals the potential of patterning the walls of a
microfluidic channel: The electro-osmotic flow can be reduced by
two orders of magnitude.
Measurements in a patterned channel will be performed with the
aim to confirm these results.
Ghent, Belgium – May 22, 2014
Research supported by IWT