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Research Papers

Using Shear and Direct Current Electric Fields to Manipulate and Self-Assemble Dielectric Particles on Microchannel Walls

[+] Author and Article Information
Necmettin Cevheri

G. W. Woodruff School
of Mechanical Engineering,
Georgia Institute of Technology,
Atlanta, GA 30332-0405
e-mail: ncevheri@gatech.edu

Minami Yoda

G. W. Woodruff School
of Mechanical Engineering,
Georgia Institute of Technology,
Atlanta, GA 30332-0405
e-mail: minami@gatech.edu

Manuscript received January 2, 2015; final manuscript received January 16, 2015; published online February 12, 2015. Editor: Boris Khusid.

J. Nanotechnol. Eng. Med 5(3), 031009 (Aug 01, 2014) (8 pages) Paper No: NANO-15-1001; doi: 10.1115/1.4029628 History: Received January 02, 2015; Revised January 16, 2015; Online February 12, 2015

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.

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References

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Ranchon, H., and Bancaud, A., 2014, private communication.

Figures

Grahic Jump Location
Fig. 5

Near-wall particle number density profiles c(h) in Poiseuille flow at γ· = 0 (×), 150 (◼), 650 (▼), 960 (●), 1250 (▲), and 1580 (◆) s−1. The dashed line denotes the bulk number density c∞ = 2.7 × 1016 m−3.

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Fig. 3

Normalized particle potential due to EO flow ΔφF/(kT) as a function of h for E = 4.7 (), 9.5 (), 16.5 (), 23.6 (), and 33.1 () V/cm

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Fig. 2

Normalized potential φ/(kT) as a function of h at E = 0 (×), 4.7 (), 9.5 (), 16.5 (), 23.6 (), and 33.1 () V/cm

Grahic Jump Location
Fig. 1

Near-wall particle number density profiles c(h) for EO flow at E = 0 (×), 4.7 (), 9.5 (), 16.5 (), 23.6 (), and 33.1 () V/cm. The dashed line denotes the bulk number density c∞ = 2.7 × 1016 m−3.

Grahic Jump Location
Fig. 6

Normalized particle potential due to Poiseuille flow ΔφF/(kT) as a function of h for γ· = 150 (◼), 650 (▼), 960 (●), 1250 (▲), and 1580 (◆) s−1

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Fig. 7

Repulsive lift force magnitude due to Poiseuille (shear) flow as a function of near-wall shear rate. The dashed line is a linear curve-fit to these data, with a correlation coefficient R2 = 0.996 [19].

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Fig. 8

Particle number density profiles c(h) measured in combined Poiseuille and EO flow at γ·= 650 (a) and 1580 s−1 (b), and E = 0 (×), 0.9 (○), 2.4 (▽), 4.7 (◻), 7.1 (◇), and 9.5 (△) V/cm. Again, the dashed line represents c∞.

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Fig. 10

Repulsive lift force magnitude due to combined Poiseuille and EO flow as a function of electric field E at γ· = 650 (●) and 1580 s−1 (▲) [19]

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Fig. 4

Log–log plot of the repulsive lift force magnitude due to EO flow as a function of electric field magnitude, both normalized by their maximum values. The solid trend line has a slope of 1, while the dashed trend line has a slope of 2.

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Fig. 11

Log–log plot of repulsive lift force magnitude due to combined flow as a function of shear rate at E = 4.7 (▼) and 9.5 (◼) V/cm. The dashed lines are power-law curve-fits to these data, and have slopes of 0.45 and 0.46 (with R2= 0.92 and 0.96), respectively [19].

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Fig. 12

Particle number density profiles c(h) measured in combined Poiseuille and EO flow at γ· = 650 (a) and 1580 s−1 (b), and E = 0 (×), −0.9 (○), −2.4 (▽), −4.7 (◻), −7.1 (◇), and −9.5 (△) V/cm.

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Fig. 13

Normalized particle potential profiles due to combined Poiseuille and EO flow ΔφF(h)/(kT) at γ· = 650 (a) and 1580 s−1 (b), and E = −0.9 (○), −2.4 (▽), −4.7 (◻), −7.1 (◇), and −9.5 (△) V/cm

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Fig. 14

Lift force due to combined Poiseuille and EO flow as a function of electric field magnitude at γ· = 650 () and 1580 () s−1

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Fig. 15

Evanescent-wave visualizations of particles in Poiseuille flow at γ· = 650 s−1 (a) and in combined EO and Poiseuille flow at E = −28 (b), −35 (c), and −70.7 (d) −95 V/cm [18]. The direction of the Poiseuille flow is from left to right in the images.

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Fig. 16

Image showing the entire ∼350 μm width of the channel with the bands (observed at γ· = 650 s−1 and E = −47 V/cm) deflecting around a piece of dust (with a diameter of ∼30 μm)

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Fig. 9

Normalized particle potential profiles due to combined Poiseuille and EO flow ΔφF(h)/(kT) at γ· = 650 (a) and 1580 s−1 (b). The legend is the same as that in Figure. 8.

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