Analysis Of Electroosmotic Flow Research Articles

Numerical simulation and experimental study of the electroosmotic flow in open microfluidic chip based on super-wettability surface

The traditional bonding technology severely limits the development of microfluidic chip owing to the complicated techniques, the blockage and deformation of microchannels, etc. In this paper, an open microfluidic chip based on super-wettability surface is proposed to avoid the bonding technology. The feasibility of open microfluidic chip based on capillary electrophoresis is demonstrated from the analysis of electroosmotic flow. In theory, we build simulation model to study the flow field of the open microchannel. The electroosmotic flow (EOF) velocity of an open microchannel (0.477 mm/s) is bascially euqal to a closed microchannel (0.479 mm/s). In experiment, the open microfluidic chip based on super-wettability surface is fabricated by chemical etching and laser ablation. The EOF velocity and electroosmotic mobility of open microfluidic chip are 1.05 mm/s and 4.2 × 10−4 cm2/(V·s), respectively. As a result, this open microfluidic chip can obtain the stable electroosmotic flow. Finally, under the action of electroosmotic flow, potassium ferricyanide is transported from the reservoir to the detection area by measuring the cyclic voltammetry curve.We envisage that this will also open up research avenues on open microfluidic chip, an area that still exists undeveloped.

COMBINED ELECTROOSMOTIC AND PRESSURE DRIVEN FLOW IN TREE-LIKE MICROCHANNEL NETWORK

The present work presents a simplified mathematical model to calculate the flowrate of the combined electroosmotic flow (EOF) and pressure driven laminar flow (PDLF) in the symmetric tree-like microchannel network under the assumptions of small zeta potential and thin electrical double layer. A numerical analysis of the combined EOF and PDLF in symmetric Y-shaped microchannel is also carried out to validate the mathematical model. The analytical results and numerical results are found to be in good agreement with each other. Using the mathematical model, the present work further investigates the effect of diameter ratio of the tree-like network on the flowrate of the combined EOF and PDLF to recognize a possible conclusion being similar to the Murray’s law. Based on the present work, it is found that the symmetric tree-like network has an optimal diameter ratio to achieve the maximum flowrate for the combined EOF and PDLF when the total microchannel volume is constant; however, this optimal diameter ratio for the combined flow disobeys the generalized Murray’s law in a simple form of power function of the branching number [Formula: see text], and it is not only related on the branching number, but also depends on the branching level and channel length ratio of the tree-like network. Furthermore, the optimal diameter ratio shows a monotonous transition from [Formula: see text] for the pure PDLF to [Formula: see text] for the pure EOF with the increasing ratio of the driven voltage and driven pressure. The present work discusses the effects of these parameters on the optimal diameter ratio for the combined EOF and PDLF.

Impact of finite ion size, Born energy difference and dielectric decrement on the electroosmosis of multivalent ionic mixtures in a nanotube

The electroosmotic flow (EOF) in a nanotube is analyzed by considering the finite ion size and dielectric decrement effects. The ion transport is governed by the modified Nernst-Planck equation, which takes into account the ion steric repulsion, Born energy difference, and dielectrophoretic force. The dielectric permittivity is considered to depend on the ionic concentration and ion size. The governing equations for fluid flow, ion transport, and electric field are solved numerically in their full form. The steric interaction is accounted, based on the Boublik–Mansoori–Carnahan–Starling–Leland (BMCSL) model, which considers the nonuniform ion size for monovalent as well as multivalent salts. We made a quantitative comparison with the standard PNP model for the lower range of charge density and highlighted the impact of ion size and dielectric decrement effects. For a highly charged surface, the impact due to finite ion size is non-negligible when the Debye length is in the order of the nanotube radius. However, the dielectric decrement is found to have a strong impact on a higher range of surface charge density or bulk ionic concentration. The EOF and the ion selectivity of the mixed electrolyte solution of different counterion size are considered in the present study. Present study provides an in-depth analysis of EOF through a cylindrical nanotube beyond the dilute solution and low charge density limits, which has not been addressed before.

Analysis of electro-osmotic flow by lattice Boltzmann simulation and Helmholtz-Smoluchowski formula

Numerical study of electro-osmotic flow (EOF) and theoretical exploration of relationship between EOF and electrical double layer (EDL) are carried out in the present work. Under the Poisson-Boltzmann and Debye-Hückel approximations, the analytic solution of electric potential, net charge, and flow pattern can be derived. The numerical results obtained by Poisson-Nernst-Planck (PNP) and Navier-Stokes equations are compared with the analytic solution and the solution based on the Helmholtz-Smoluchowski formula. Also, this article provides a clearer view on nondimensionalization applied on lattice Boltzmann method with different differential equation.

The Effects of Finite Ionic Sizes and Wall Slip on Entropy Generation in Electroosmotic Flows in a Soft Nanochannel

Abstract The combined effects of finite ionic sizes and boundary slip on the entropy generation in mixed pressure driven and electroosmotic flows (EOFs) in a soft nanochannel are investigated in this study. The soft nanochannel is represented by a rigid nanochannel covered by a charged polyelectrolyte layer (PEL) on its surface. The entropy generation analysis of EOFs in such a soft nanochannel is addressed for the first time. Under the assumption of high zeta potentials, the electric potential, velocity, and temperature distributions are obtained numerically by using the finite difference method. Subsequently, the thermal transport characteristic and the corresponding entropy generation analysis are discussed based on the obtained velocity and temperature distributions. Our results show that the soft nanochannel in the present model is not appropriate for cooling purposes. We also demonstrate that the steric factor v and the PEL thickness d can enhance the entropy generation rate. However, the slip boundary coefficient γ, the drag parameter α, and the equivalent electric double-layer (EDL) thickness λFCL can restrain this entropy generation rate. In addition, the contributions of Joule heating and viscous friction in the entropy generation rate are more prominent than the contribution due to heat transfer. The present theoretical research can be used to design the efficient thermofluidic devices.

Numerical simulation of electroosmotic flow in rough microchannels using the lattice Poisson-Nernst-Planck methods

In this study, coupled Lattice Boltzmann method is applied to solve the dynamic model for an electroosmotic flow and investigate the effects of roughness in a 2-D flat microchannel. In the present model, the Poisson equation is solved for the electrical potential, the Nernst– Planck equation is solved for the ion concentration. In the analysis of electroosmotic flows, when the electric double layers fully overlap or the convective effects are not negligible, the Nernst-Planck equation must be used to find the ionic distribution throughout the microchannel. The effects of surface roughness height, roughness interval spacing and roughness surface potential on flow conditions are investigated for two different configurations of the roughness, when the EDL layers fully overlap through the microchannel. The results show that in both arrangements of roughness in homogeneously charged rough channels, the flow rate decreases by increasing the roughness height. A discrepancy in the mass flow rate is observed when the roughness height is about 0.15 of the channel width, which its average is higher for the asymmetric configuration and this difference grows by increasing the roughness height. In the symmetric roughness arrangement, the mass flow rate increases until the roughness interval space is almost 1.5 times the roughness width and it decreases for higher values of the roughness interval space. For the heterogeneously charged rough channel, when the roughness surface potential ψr is less than channel surface potential ψs, the net charge density increases by getting far from the roughness surface, while in the opposite situation, when ψs is more than ψr, the net charge density decreases from roughness surface to the microchannel middle center. Increasing the roughness surface potential induces stronger electric driving force on the fluid which results in larger velocities in the flow.

Analysis of electro-osmotic flow over a slightly bumpy plate

The present study is aimed to investigate the effects of wavy roughness on electro-osmotic (EO) flow over a wavy plate. The waviness of the plate is modeled by the product of two cosinoidal functions, and the roughness (ε) is defined to be the ratio of the wavy amplitude to the Debye length. The effects are examined with respect to the roughness ε and different wave numbers (α and β) of the plate waviness. The analysis of the EO flow over the wavy plate is carried out for the applied electric potential, the potential for the electric double layer, as well as the EO flow velocity and pressure field under the Debye-Hückel approximation by using a boundary perturbation method. It is found that the velocity component along the direction of the applied electric field is modified by a second-order term of the roughness, though the same velocity component near the wavy wall exhibits periodic behaviors in phase with the plate waviness. The mean flow rate deficit (ε2μ2) due to the surface roughness presents a sophisticated dependence on the longitudinal wave number (α) and transverse wave number (β) of the plate waviness, yet the flow deficit is linear in α for small α at β = 0, and shows a long wavelength limit singularity at β = 0 for α ≠ 0.

Analysis of electroosmotic flow and Joule heating effect in a hydrophobic channel

In this paper, a mathematical model has been developed to analyze the fluid flow and heat transfer effect in a hydrophobic microchannel filled with a power law fluid. The effects of Joule heating, thermal radiation and velocity slip boundary conditions are analyzed by considering different slip parameters, EDL thickness, pressure gradient and flow behavior indices. The analytical expression for fluid flow and heat transfer have been derived in terms of the flow governing parameters based on the Debye-Huckel linearizing principle. Depending on the experimental existing flow behavior index, the analytical solutions are obtained in closed form where as numerical results are presented for general parametric values. The impact of slip velocity parameters in terms of a flow enhancement factor (Efb), is studied to obtain the average flow velocity variation in a hydrophobic microchannel compared to a plane microchannel. The pressure assisted flow for pseudo-plastic (shear thinning) fluids achieve maximum velocity as compared to dilatant (shear thickening) fluids. The study finds that increase in thermal radiation minimizes heat transfer rate close to the hydrophobic wall, plays a vital role for the therapeutic treatment of hyperthermia (to understand the effect of heat transfer due to electric potential). It is also observed that Joule heating parameters enhance the heat transfer rate for classical Newtonian/non-Newtonian fluids for decrease in power indices and pressure gradient.

Analysis of electro-osmotic flow in a microchannel with undulated surfaces

The electro-osmotic flow through a channel between two undulated surfaces induced by an external electric field is investigated. The gap of the channel is very small and comparable to the thickness of the electrical double layers. A lattice Boltzmann simulation is carried out on the model consisting of the Poisson equation for electrical potential, the Nernst–Planck equation for ion concentration, and the Navier–Stokes equations for flows of the electrolyte solution. An analytical model that predicts the flow rate is also derived under the assumption that the channel width is very small compared with the characteristic length of the variation along the channel. The analytical results are compared with the numerical results obtained by using the lattice Boltzmann method. In the case of a constant surface charge density along the channel, the variation of the channel width reduces the electro-osmotic flow, and the flow rate is smaller than that of a straight channel. In the case of a surface charge density distributed inhomogeneously, one-way flow occurs even under the restriction of a zero net surface charge along the channel.

Numerical Simulation of Electroosmotic Flow in Flat Microchannels with Lattice Boltzmann Method

In the present work, a new Lattice Boltzmann model has been developed to study the electroosmotic flows in a 2-D flat microchannel. The governing equations are presented in the continuum model, while a set of equivalent equations in Lattice Boltzmann model is introduced and solved numerically. In particular, the Poisson and the Nernst–Planck (NP) equations are solved by two new lattice evolution methods. In the analysis of electroosmotic flows, when the convective effects are not negligible or the electric double layers have overlap, the NP equations must be employed to determine the ionic distribution throughout the microchannel. The results of this new model have been validated by available analytical and numerical results. The model has also been used to examine the electroosmotic flows in a heterogeneous flat microchannel. Furthermore, the predictions of the NP model are compared with those of the Poisson Boltzmann (PB) equation to identify the applicability of the PB equations for such flows, which can also serve as validations for the present model.

Numerical analysis of electro-osmotic flows through elliptic microchannels

This work presents a comprehensive numerical analysis of electro-osmotically driven flows inside microchannels characterized by an elliptic cross-section. The mathematical model takes into account the presence of an opposing pressure gradient to correctly reproduce the operating conditions of pumps. The dynamical features are analyzed for isothermal flows in the fully developed region. Characteristic curves that relate the volumetric flow rate and the pressure head are presented with respect to all the non-dimensional parameters that influence the behavior of combined electroosmotic/ pressure-driven flows, i.e., the aspect ratio of the cross-section, the electrokinetic diameter, the non-dimensional zeta-potential and the ratio of the pressure force to the electric force. Such numerical results are also compared with two existing correlations for microchannels with rectangular or trapezoidal cross-sections, that assess both volumetric flow rate and pressure head. The comparison highlights that the correlation for the volumetric flow rate works perfectly also for this kind of geometry, while a correction is proposed for the pressure head estimate, in order to extend the validity of the original correlation to elliptic microchannels.

Analysis of electroosmotic flow with periodic electric and pressure fields via the lattice Poisson–Boltzmann method

This paper analyzes the electroosmotic flow fields in heterogeneous microchannels by applying the lattice Poisson–Boltzmann equation. The influences of surface potential, ionic molar concentration, channel height, and driving force fields on fluid velocity are discussed in detail. A scheme for producing vortexes in a straight channel by adjusting the heterogeneous surface potentials and phase angles of the periodic driving force fields is introduced. By distributing the heterogeneous surface potentials at particular positions, we can create vortexes near walls or in the center of the channel. The size, strength, and rotational direction of vortexes are further variable by introducing appropriate phase angles for a single driving force field or for the phase differences between combined driving force fields, such as electric/pressure fields. These obstacle-like vortexes perturb fluids and hinder flow, and thus, may be useful for enhancing micromixer performance.

Electroviscous effects in purely pressure driven flow and stationary plane analysis in electroosmotic flow of power-law fluids in a slit microchannel

This paper is a comprehensive work on flow of power-law fluids in a slit microchannel. The first part of the paper deals with study of electrokinetic effects in steady, fully developed, laminar pressure driven flow of power-law fluids. The second part of the work provides analysis of stationary plane that is formed during electroosmotic flow (EOF) of power-law fluids inside a closed slit microchannel. In the entire analysis, the flow of power-law fluid is characterized by the modified Navier–Stokes equation incorporating the electric body force term. The electric double layer (EDL) potential is described by the Poisson–Boltzmann distribution under Debye Hückel approximation. In pressure driven flow, analytical expressions for velocity profiles of various power-law fluids are obtained for n = 1, 1/2, 1/3. Numerical simulation is carried out for all values of n to find induced streaming potential without any approximations for entire range of flow behavior indices. The analytical solutions are compared with numerical results. The effects of flow behavior index, zeta potential and channel dimension on velocity distribution, streaming potential, apparent viscosity, volumetric flow rate and friction coefficient are discussed. In the analysis of EOF in closed slit microchannel, the positions of stationary planes for various flow behavior indices at different EDL thicknesses are found both analytically and numerically. It is found that the electroosmotic counter pressure developed inside the cell is strongly dependent on zeta potential and weakly dependent on EDL thickness.

Electro-osmotic flow in microchannels

In the current study, the modified Navier—Stokes equations together with the Poisson—Boltzmann and Laplace equations have been used to numerically model electro-osmotic flow (EOF) in straight microchannels. Flow experiments have been carried out using microchannels etched into silicon wafer surfaces. The numerical results from the present study have been compared against experimental data and an analytical solution. The results indicate that the numerical simulations are an accurate representation of EOF and that this model could be used as a tool in the design and analysis of complex EOF driven systems.

1010 多数の分岐を有する微小流路内における電気浸透流の計測(GS-5 流体計測)

1010 多数の分岐を有する微小流路内における電気浸透流の計測(GS-5 流体計測)

Comparison of the Nernst–Planck model and the Poisson–Boltzmann model for electroosmotic flows in microchannels

In the analysis of electroosmotic flows, the internal electric potential is usually modeled by the Poisson-Boltzmann equation. The Poisson-Boltzmann equation is derived from the assumption of thermodynamic equilibrium where the ionic distributions are not affected by fluid flows. Although this is a reasonable assumption for steady electroosmotic flows through straight microchannels, there are some important cases where convective transport of ions has nontrivial effects. In these cases, it is necessary to adopt the Nernst-Planck equation instead of the Poisson-Boltzmann equation to model the internal electric field. In the present work, the predictions of the Nernst-Planck equation are compared with those of the Poisson-Boltzmann equation for electroosmotic flows in various microchannels where the convective transport of ions is not negligible.

201 多数の分岐を有する微小流路内における電気浸透流の数値解析(OS-2 マイクロ・ナノ流体工学(1))

201 多数の分岐を有する微小流路内における電気浸透流の数値解析(OS-2 マイクロ・ナノ流体工学(1))

Analysis of electroosmotic flow in a microchannel packed with microspheres

The electroosmotic flow in a microchannel packed with microspheres under both direct and alternating electric fields is analyzed. In the case of the steady DC electroosmosis in a packed microchannel, the so-called “capillary model” is used, in which it is assumed that a porous medium is equivalent to a series of intertwined tubules. The interstitial tubular velocity is obtained by analytically solving the Navier–Stokes equation and the complete Poisson–Boltzmann equation. Then, using the volume-averaging method, the solution for the electroosmotic flow in a single charged cylindrical tubule is applied to estimate the electroosmosis in the overall porous media by introducing the porosity and tortuosity. Assuming uniform porosity, an exact solution accounting for the electrokinetic wall effect is obtained by solving the modified Brinkman momentum equation. For the electroosmotic flow under alternating electric fields in a cylindrical microchannel packed with microspheres of uniform size, two different conditions regarding the openness of the channel ends are considered. Based on the capillary model, the time-periodic oscillating electroosmotic flow in an open-ended microchannel in response to the application of an alternating electric field is obtained using the Green’s function approach to the Navier–Stokes equation. When the two ends of the channel are closed, a backpressure is induced to generate a counter flow, resulting in a new zero flow rate. Such induced backpressure associated with the counter flow in a closed-end microchannel is obtained analytically by solving the transient modified Brinkman momentum equation.

Analysis of electroosmotic flow with step change in zeta potential

The term electroosmotic flow refers to the bulk flow of an aqueous solution induced by the application of the electric field to the zeta potential. The characteristics of EOF in a microchannel depend upon the nature of the zeta potential, i.e., whether it is uniform or nonuniform. In this study, the full Navier–Stokes equation and the Nernst–Planck equation are used to model the change in EOF characteristics that occur when a step change in zeta potential is applied. It is found that the thickness of the electrical double layer gradually increases downstream from the location at which the zeta potential is increased. The results indicate that a step change in zeta potential causes a significant variation in the velocity profile and in the pressure distribution.

Visualization and analysis of electroosmotic flow in hairless mouse skin.

To identify the physiological structures in hairless mouse skin responsible for the generation of electroosmotic flow during iontophoresis. Also, to determine the effects of changing the pH of the contacting solution on the magnitude of electroosmotic flow in these structures. Localized diffusive and iontophoretic fluxes of a neutral molecule, hydroquinone (HQ), across hairless mouse skin were quantified using scanning electrochemical microscopy (SECM). The iontophoretic flux was determined as a function of the direction of the applied current and pH of the contacting solution. SECM images of HQ transport recorded during iontophoresis at moderate current densities (+/-0.1 mA/cm2) demonstrate that electroosmotic flow is localized to hair follicles. The direction of flow is from anode to cathode at pH > 3.5 and from cathode to anode at pH <3.5. Electroosmotic flow through hair follicles is an efficient and controllable means of transporting small, electrically neutral molecules across hairless mouse skin. Transport through the appendages is sensitive to the pH of the solution in contact with the skin. The isoelectric point of hair follicles, pI, is estimated to be 3.5 from the dependence of electroosmotic flow on the solution pH.