Lubrication theory for electro-osmotic flow in a microfluidic channel of slowly varying cross-section and wall charge

2002 ◽  
Vol 459 ◽  
pp. 103-128 ◽  
Author(s):  
SANDIP GHOSAL
Keyword(s):  
Cross Section ◽  
Microfluidic Channel ◽  
Lubrication Theory ◽  
Wall Material ◽  
Channel Cross Section ◽  
Microfluidic Channels ◽  
Osmotic Flow ◽  
Axial Variation ◽  
Wall Charge ◽  
Electro Osmotic Flow

Electro-osmotic flow is a convenient mechanism for transporting fluid in microfluidic devices. The flow is generated through the application of an external electric field that acts on the free charges that exist in a thin Debye layer at the channel walls. The charge on the wall is due to the particular chemistry of the solid–fluid interface and can vary along the channel either by design or because of various unavoidable inhomogeneities of the wall material or because of contamination of the wall by chemicals contained in the fluid stream. The channel cross-section could also vary in shape and area. The effect of such variability on the flow through microfluidic channels is of interest in the design of devices that use electro-osmotic flow. The problem of electro-osmotic flow in a straight microfluidic channel of arbitrary cross-sectional geometry and distribution of wall charge is solved in the lubrication approximation, which is justified when the characteristic length scales for axial variation of the wall charge and cross-section are both large compared to a characteristic width of the channel. It is thereby shown that the volume flux of fluid through such a microchannel is a linear function of the applied pressure drop and electric potential drop across it, the coefficients of which may be calculated explicitly in terms of the geometry and charge distribution on the wall. These coefficients characterize the ‘fluidic resistance’ of each segment of a microfluidic network in analogy to the electrical ‘resistance’ in a microelectronic circuit. A consequence of the axial variation in channel properties is the appearance of an induced pressure gradient and an associated secondary flow that leads to increased Taylor dispersion limiting the resolution of electrophoretic separations. The lubrication theory presented here offers a simple way of calculating the distortion of the flow profile in general geometries and could be useful in studies of dispersion induced by inhomogeneities in microfluidic channels.

scholarly journals Simultaneous Pumping and Mixing of Biological Fluids in a Double-Array Electrothermal Microfluidic Device

Micromachines ◽  
2019 ◽  
Vol 10 (2) ◽  
pp. 92 ◽  
Author(s):  
Alinaghi Salari ◽  
Colin Dalton
Keyword(s):  
Cross Section ◽  
Fluid Transport ◽  
Biological Fluids ◽  
Microfluidic Channel ◽  
Lab On A Chip ◽  
Channel Cross Section ◽  
Mixing Efficiency ◽  
Electrode Pair ◽  
Transverse Mixing ◽  
Double Array

Transport and mixing of minute amounts of biological fluids are significantly important in lab-on-a-chip devices. It has been shown that the electrothermal technique is a suitable candidate for applications involving high-conductivity biofluids, such as blood, saliva, and urine. Here, we introduce a double-array AC electrothermal (ACET) device consisting of two opposing microelectrode arrays, which can be used for simultaneous mixing and pumping. First, in a 2D simulation, an optimum electrode-pair configuration capable of achieving fast transverse mixing at a microfluidic channel cross-section is identified by comparing different electrode geometries. The results show that by adjusting the applied voltage pattern and position of the asymmetrical microelectrodes in the two arrays, due to the resultant circular flow streamlines, the time it takes for the analytes to be convected across the channel cross-section is reduced by 95% compared to a diffusion-only-based transport regime, and by 80% compared to a conventional two-layer ACET device. Using a 3D simulation, the fluid transport (pumping and mixing) capabilities of such an electrode pair placed at different angles longitudinally relative to the channel was studied. It was found that an asymmetrical electrode configuration placed at an angle in the range of 30 ° ≤ θ ≤ 45 ° can significantly increase transversal mixing efficiency while generating strong longitudinal net flow. These findings are of interest for lab-on-a-chip applications, especially for biosensors and immunoassays, where mixing analyte solutions while simultaneously moving them through a microchannel can greatly enhance the sensing efficiency.

scholarly journals Transport of particles and microorganisms in microfluidic channels using rectified ac electro-osmotic flow

2011 ◽  
Vol 5 (1) ◽  
pp. 013407 ◽  
Author(s):  
Wen-I Wu ◽  
P. Ravi Selvaganapathy ◽  
Chan Y. Ching
Keyword(s):  
Microfluidic Channels ◽  
Osmotic Flow ◽  
Electro Osmotic Flow

Electro-osmotic flow of electrolyte solutions of PEO in microfluidic channels

2020 ◽  
Vol 563 ◽  
pp. 381-393 ◽  
Author(s):  
Pantelis Moschopoulos ◽  
Yannis Dimakopoulos ◽  
John Tsamopoulos
Keyword(s):  
Electrolyte Solutions ◽  
Microfluidic Channels ◽  
Osmotic Flow ◽  
Electro Osmotic Flow

Lubrication theory for electro-osmotic flow in a non-uniform electrolyte

2007 ◽  
Vol 576 ◽  
pp. 139-172 ◽  
Author(s):  
T. L. SOUNART ◽  
J. C. BAYGENTS
Keyword(s):  
Electric Field ◽  
Electric Fields ◽  
Numerical Solutions ◽  
Fluid Velocity ◽  
Lubrication Theory ◽  
Debye Screening Length ◽  
Sample Stacking ◽  
Osmotic Flow ◽  
Analytic Expressions ◽  
Electro Osmotic Flow

A lubrication theory has been developed for the electro-osmotic flow of non-uniform buffers in narrow rectilinear channels. The analysis applies to systems in which the transverse dimensions of the channel are large compared with the Debye screening length of the electrolyte. In contrast with related theories of electrokinetic lubrication, here the streamwise variations of the velocity field stem from, and are nonlinearly coupled to, spatiotemporal variations in the electrolyte composition. Spatially non-uniform buffers are commonly employed in electrophoretic separation and transport schemes, including iso-electric focusing (IEF), isotachophoresis (ITP), field-amplified sample stacking (FASS), and high-ionic-strength electro-osmotic pumping. The fluid dynamics of these systems is controlled by a complex nonlinear coupling to the ion transport, driven by an applied electric field. Electrical conductivity gradients, attendent to the buffer non-uniformities, result in a variable electro-osmotic slip velocity and, in electric fields approaching 1 kV cm−1, Maxwell stresses drive the electrohydrodynamic circulation. Explicit semi-analytic expressions are derived for the fluid velocity, stream function, and electric field. The resulting approximations are found to be in good agreement with full numerical solutions for a prototype buffer, over a range of conditions typical of microfluidic systems. The approximations greatly simplify the computational analysis, reduce computation times by a factor 4–5, and, for the first time, provide general insight on the dominant fluid physics of two-dimensional electrically driven transport.

scholarly journals Mapping inertial migration in the cross section of a microfluidic channel with high-speed imaging

2020 ◽  
Vol 6 (1) ◽  
Author(s):  
Jian Zhou ◽  
Zhangli Peng ◽  
Ian Papautsky
Keyword(s):  
Cross Section ◽  
High Speed ◽  
Microfluidic Channel ◽  
Channel Cross Section ◽  
High Speed Imaging ◽  
Cross Sectional ◽  
Inertial Migration ◽  
Imaging Results ◽  
New Findings ◽  
Migration Pathways

AbstractThe wide adoption of inertial microfluidics in biomedical research and clinical settings, such as rare cell isolation, has prompted the inquiry of its underlying mechanism. Although tremendous improvement has been made, the mechanism of inertial migration remains to be further elucidated. Contradicting observations are not fully reconciled by the existing theory, and details of the inertial migration within channel cross sections are missing in the literature. In this work, for the first time, we mapped the inertial migration pathways within channel cross section using high-speed imaging at the single-particle level. This is in contrast to the conventional method of particle streak velocimetry (PSV), which provides collective information. We also applied smoothed particle hydrodynamics (SPH) to simulate the transient motion of particles in 3D and obtained cross-sectional migration trajectories that are in agreement with the high-speed imaging results. We found two opposing pathways that explain the contradicting observations in rectangular microchannels, and the force analysis of these pathways revealed two metastable positions near the short walls that can transition into stable positions depending on the flow condition and particle size. These new findings significantly improve our understanding of the inertial migration physics, and enhance our ability to precisely control particle and cell behaviors within microchannels for a broad range of applications.

A mathematical model of mixing enhancement in microfluidic channel with a constriction under periodic electro-osmotic flow

2012 ◽  
Vol 100 (4) ◽  
pp. 041907 ◽  
Author(s):  
Zhongbin Xu ◽  
Yue Yang ◽  
Damien Vadillo ◽  
Xiaodong Ruan ◽  
Xin Fu
Keyword(s):  
Mathematical Model ◽  
Microfluidic Channel ◽  
Mixing Enhancement ◽  
Osmotic Flow ◽  
Electro Osmotic Flow
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