Manipulating suspended neutrally buoyant colloidal particles of radii a = O (0.1–1 μm) near solid surfaces, or walls, is a key technology in various microfluidics devices. These particles, suspended in an aqueous solution at rest near a solid surface, or wall, are subject to wall-normal “lift” forces described by the Derjaguin–Landau–Verwey–Overbeek (DLVO) theory of colloid science. The particles experience additional lift forces, however, when suspended in a flowing solution. A fundamental understanding of such lift forces could therefore lead to new methods for the transport and self-assembly of particles near and on solid surfaces. Various studies have reported repulsive electroviscous and hydrodynamic lift forces on colloidal particles in Poiseuille flow (with a constant shear rate γ· near the wall) driven by a pressure gradient. A few studies have also observed repulsive dielectrophoretic-like lift forces in electroosmotic (EO) flows driven by electric fields. Recently, evanescent-wave particle tracking has been used to quantify near-wall lift forces on a = 125–245 nm polystyrene (PS) particles suspended in a monovalent electrolyte solution in EO flow, Poiseuille flow, and combined Poiseuille and EO flow through ∼30 μm deep fused-silica channels. In Poiseuille flow, the repulsive lift force appears to be proportional to γ·, a scaling consistent with hydrodynamic, versus electroviscous, lift. In combined Poiseuille and EO flow, the lift forces can be repulsive or attractive, depending upon whether the EO flow is in the same or opposite direction as the Poiseuille flow, respectively. The magnitude of the force appears to be proportional to the electric field magnitude. Moreover, the force in combined flow exceeds the sum of the forces observed in EO flow for the same electric field and in Poiseuille flow for the same γ·. Initial results also imply that this force, when repulsive, scales as γ·1/2. These results suggest that the lift force in combined flow is fundamentally different from electroviscous, hydrodynamic, or dielectrophoretic-like lift. Moreover, for the case when the EO flow opposes the Poiseuille flow, the particles self-assemble into dense stable periodic streamwise bands with an average width of ∼6 μm and a spacing of 2–4 times the band width when the electric field magnitude exceeds a threshold value. These results are described and reviewed here.

References

References
1.
Reyes
,
D. R.
,
Iossifidis
,
D.
,
Auroux
,
P. A.
, and
Manz
,
A.
,
2002
, “
Micro Total Analysis Systems. 1. Introduction, Theory, and Technology
,”
Anal. Chem.
,
74
(
12
), pp.
2623
2636
.10.1021/ac0202435
2.
Lim
,
C. T.
, and
Zhang
,
Y.
,
2007
, “
Bead-Based Microfluidic Immunoassays: The Next Generation
,”
Biosens. Bioelectron.
,
22
(
7
), pp.
1197
1204
.10.1016/j.bios.2006.06.005
3.
Probstein
,
R. F.
,
2003
,
Physicochemical Hydrodynamics: An Introduction
,
2nd ed.
,
Wiley
,
Oxford, UK,
Chap. 8.
4.
Stone
,
H. A.
, and
Kim
,
S.
,
2001
, “
Microfluidics: Basic Issues, Applications, and Challenges
,”
AIChE J.
,
47
(
6
), pp.
1250
1254
.10.1002/aic.690470602
5.
Alexander
,
B. M.
, and
Prieve
,
D. C.
,
1987
, “
A Hydrodynamic Technique for Measurement of Colloidal Forces
,”
Langmuir
,
3
(
5
), pp.
788
795
.10.1021/la00077a038
6.
Bike
,
S. G.
,
Lazarro
,
L.
, and
Prieve
,
D. C.
,
1995
, “
Electrokinetic Lift of a Sphere Moving in Slow Shear Flow Parallel to a Wall I. Experiment
,”
J. Colloid Interface Sci.
,
175
(
2
), pp.
411
421
.10.1006/jcis.1995.1471
7.
Bike
,
S. G.
, and
Prieve
,
D. C.
,
1992
, “
Electrohydrodynamics of Thin Double Layers: A Model for the Streaming Potential Profile
,”
J. Colloid Interface Sci.
,
154
(
1
), pp.
87
96
.10.1016/0021-9797(92)90080-6
8.
Cox
,
R. G.
,
1997
, “
Electroviscous Forces on a Charged Particle Suspended in a Flowing Liquid
,”
J. Fluid Mech.
,
338
, pp.
1
34
.10.1017/S0022112097004862
9.
Warszyński
,
P.
,
Wu
,
X.
, and
van de Ven
,
T. G. M.
,
1998
, “
Electrokinetic Lift Force for a Charged Particle Moving Near a Charged Wall—A Modified Theory and Experiment
,”
Colloids Surf. A
,
140
(
1–3
), pp.
183
198
.10.1016/S0927-7757(97)00277-X
10.
Williams
,
P. S.
,
Moon
,
M. H.
,
Xu
,
Y.
, and
Giddings
,
J. C.
,
1996
, “
Effect of Viscosity on Retention Time and Hydrodynamic Lift Forces in Sedimentation/Steric Field-Flow Fractionation
,”
Chem. Eng. Sci.
,
51
(
19
), pp.
4477
4488
.10.1016/0009-2509(96)00291-6
11.
Cox
,
R. G.
, and
Brenner
,
H.
,
1968
, “
The Lateral Migration of Solid Particles in Poiseuille Flow—I. Theory
,”
Chem. Eng. Sci.
,
23
(
2
), pp.
147
173
.10.1016/0009-2509(68)87059-9
12.
Yariv
,
E.
,
2006
, “‘
Force-Free’ Electrophoresis
?,”
Phys. Fluids
,
18
(
3
), p.
031702
.10.1063/1.2185690
13.
Liang
,
L.
,
Ai
,
Y.
,
Zhu
,
J.
,
Qian
,
S.
, and
Xuan
,
S.
,
2010
, “
Wall-Induced Lateral Migration in Particle Electrophoresis Through a Rectangular Microchannel
,”
J. Colloid Interface Sci.
,
347
(
1
), pp.
142
146
.10.1016/j.jcis.2010.03.039
14.
Kazoe
,
Y.
, and
Yoda
,
M.
,
2011
, “
An Experimental Study of the Effect of External Electric Fields on Interfacial Dynamics of Colloidal Particles
,”
Langmuir
,
27
(
18
), pp.
11481
11488
.10.1021/la202056b
15.
Dutta
,
P.
, and
Beskok
,
A.
,
2001
, “
Analytical Solution of Combined Electroosmotic/Pressure Driven Flows in Two-Dimensional Straight Channels: Finite Debye Layer Effects
,”
Anal. Chem.
,
73
(
9
), pp.
1979
1986
.10.1021/ac001182i
16.
Monazami
,
R.
, and
Manzari
,
M. T.
,
2007
, “
Analysis of Combined Pressure-Driven Electroosmotic Flow Through Square Microchannels
,”
Microfluid. Nanofluid.
,
3
(
1
), pp.
123
126
.10.1007/s10404-005-0065-4
17.
Barz
,
D. P. J.
,
Zadeh
,
H. F.
, and
Ehrhard
,
P.
,
2011
, “
Measurements and Simulations of Time-Dependent Flow Fields Within an Electrokinetic Micromixer
,”
J. Fluid Mech.
,
676
, pp.
265
293
.10.1017/jfm.2011.44
18.
Cevheri
,
N.
, and
Yoda
,
M.
,
2014
, “
Electrokinetically Driven Reversible Banding of Colloidal Particles Near the Wall
,”
Lab Chip
,
14
(
8
), pp.
1391
1394
.10.1039/c3lc51341f
19.
Cevheri
,
N.
, and
Yoda
,
M.
,
2014
, “
Lift Forces on Colloidal Particles in Combined Electroosmotic and Poiseuille Flow
,”
Langmuir
,
30
(
46
), pp.
13771
13780
.10.1021/la502290y
20.
Ranchon
,
H.
, and
Bancaud
,
A.
, 2014, private communication.
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