Electroosmotic Pump Research Articles

Analysis of the effects of inclination and configuration of the electroosmotic field on the cooling performance of a microchannel

The study investigates the effect of using electroosmotic pumps on the cooling of electrical devices in micro scales. The mutual effects of the microchannel inclination (ranging from 0° to 75°) and configuration of the electric field on the heat transfer have not been investigated. To this end, a numerical code based on the finite volume method (FVM) and Semi-Implicit Method for Pressure Linked Equations (SIMPLE) was developed in Fortran to model the two-dimensional flow dynamics and heat transfer. Two different arrangements were considered for the discrete heat sources and electroosmotic fields to examine their effects on fluid dynamics and heat transfer rate at Re=10. In addition, the effects of electrical parameters, which directly affect the flow dynamics, were also considered. Results indicate that decreasing the heat transfer rate at higher angles is because of the velocity mitigation, whereas an increase in the Grashof number causes a reverse effect. Altering the layout of heaters and electric field from the condition in which heat sources are facing each other (Arrangement 1) to the condition in which heat sources are not facing each other (Arrangement 2), leads to the formation of swirling flow, increased flow rate, and decreased average Nusselt number. The optimum configuration for maximum cooling performance is found in Arrangement 1 with the Grashof number of 0 and inclination angle of 0°, in which the highest average Nusselt number of 5.815 is achieved. Despite the reduction in cooling efficiency at higher angles, Arrangement 1 outperforms Arrangement 2.

Bonding evolution in PbO@C composites for lead-carbon battery: Implications for HRPSoC performance

Due to the huge density difference between lead and carbon, the strength of the bonding between lead and carbon materials plays a key role in lead-carbon batteries (LCBs). Here, the evolution and transformation of Pb and C bonding in the negative active materials (NAMs) were studied throughout the battery fabrication process of curing, formation and charge/discharge cycles. The results indicate PbC bond in the PbO@C composite is cleaved by chemical reactions during the curing and formation process. In addition, the graphitization degree of the carbon material decreased after charge/discharge cycles. Compared with the blank lead-acid battery, the initial capacity and high-rate partial state of charge (HRPSoC) cycle life of lead-carbon with PbO@C composite significantly increase. The previous sites of Pb and C after the transformation of lead and its compounds can still act as active sites for the reaction of NAMs in curing, formation and charge/discharge cycles. Meanwhile, the porous carbon material in PbO@C can act as a supporting skeleton and a 3D electroosmotic pump, which is beneficial for the interaction between the electrolyte and the negative electrode active substance, attributing to the boosted performance of lead-carbon battery. This work provides theoretical support for understanding the lead-carbon binding mechanism during the operation of lead-carbon batteries.

Generalizing electroosmotic-flow predictions over charge-modulated periodic topographies: tuneable far-field effects

The classical Helmholtz–Smoluchowski (HS) model of electroosmosis holds for homogeneously charged interfaces in contact with a fluid layer bearing an equal and opposite net charge. However, inhomogeneities in the surface charge and topography are inevitable, either as practical materials and fabrication artefacts, or at times as deliberately introduced modulations for flow control. In an effort to arrive at an analytically tractable theoretical framework for addressing the underlying electro-mechanical coupling, here, we generalize the traditional HS theory to an extent where both the surface charge and topographies may bear arbitrary and independent periodic forms. Using a spectral-asymptotic approach, we further arrive at closed-form expressions for describing the resulting electroosmotic pumping for topographic features with small characteristic amplitude to pattern period ratio, as relevant for most practical scenarios. We subsequently execute full-scale numerical simulations without any restrictions on the surface charge and topography variations to assess the efficacy of the theoretical framework. The corresponding test beds include distinctive signature patterns – for example, a square-wave surface charge distribution on trapezoidal pit topographies. Our results reveal that the charge–topography interplay induces an anisotropic flow drift, deviating from the classical HS paradigm. This, in turn, provides new quantitative insights into highly selective electroosmotic flow control via judicious design of the charge and topographical patterns, resulting in controllable accentuation, attenuation, nullification, deflection and even complete reversal of the flow. Our analysis further establishes a provision of estimating the zeta potentials of naturally ‘contaminated’ surfaces, as well as explaining the electrophoresis of large inhomogeneous particles; a paradigm that remained to be explored thus far.

In-situ carbon encapsulated Pb/PbO nanoparticles derived from spent lead paste for lead-carbon battery

The sulfation and serious hydrogen evolution reaction render a substantial obstacle for the further development of lead-carbon batteries (LCBs). Herein, lead tartrate precursors derived from spent lead paste are pyrolyzed to in-situ synthesize a carbon encapsulated Pb/PbO nanoparticles, which are introduced as additives into the negative electrodes of LCBs. The in-situ formed carbon encapsulation Pb/PbO nanoparticles ensure the long-lasting inhibition of the hydrogen evolution reaction in the negative electrodes. The discharge capacity after the introduction of the composites is improved by 24 % compared with the control at 0.1C, and the cycle life is almost twice as long as the control. The remarkable hydrophilicity of the composites as 3D electro-osmotic pumps facilitates the absorption and transportation of electrolyte to the negative active materials. Additionally, the carbon encapsulated Pb/PbO nanoparticles could provide abundant nucleation sites for Pb/PbSO4 conversion and reinforce the reversibility of the transformation between the substances. Benefiting the cooperative interaction between the multiple mechanisms in the composites, the sulfation and serious hydrogen evolution on the negative electrode are dramatically inhibited, consequently thus contributing to the admirable promotion of the overall performances of LCBs.

96‐1: Invited Paper: Flat Panel Haptics: Embedded Electroosmotic Pumps for Scalable Shape Displays

The flat, featureless nature of touch screen displays has meant keyboard text entry is slower and more error‐prone than on mechanical counterparts, and has also introduced negative side effects in demanding settings like automotive. Ideally, we could maintain the graphical flexibility afforded by displays, but carry over the tactile benefits of physical keyboard keys and buttons. Flat panel haptic displays have the potential to achieve this.We present a new type of shape‐changing display using embedded electroosmotic pumps (EEOPs). Our pumps are 1.5mm in thickness, and allow complete stack‐ups under 5mm with the opportunity to become much thinner. Our EEOPs can move their entire volume's worth of fluid in 1 second, and apply pressures of +/‐50kPa. This is enough to create dynamic, mm scale tactile features on a surface.

Integrated analysis of electroosmotic and magnetohydrodynamic peristaltic pumping in physiological systems: Implications for biomedical applications

AbstractThe study of rheological properties in biological fluids, influenced by electroosmosis and magnetohydrodynamic (MHD) peristaltic mechanisms, plays a vital role in designing micro‐scale biomimetic pumping systems for targeted drug delivery. Considering these significant applications, the current study focuses on the integrated analysis of electroosmotic and magnetohydrodynamic peristaltic pumping of Williamson fluid within physiological systems with variable viscosity and thermal conductivity. The dimensional momentum equations are linearized under the approximation of lubrication theory. The current study deals with the impact of various physical parameters on flow, heat transfer, and pumping characteristics. These parameters include the magnetic parameter, variable viscosity, variable thermal conductivity, Helmholtz‐Smoluchowski velocity, and so on. It is noted from the current analysis that, Helmholtz‐Smoluchowski velocity and velocity slip parameters have decreasing effect on skin friction and Sherwood number. The electroosmotic and magnetic parameters contribute to larger trapped bolus sizes. These findings contribute significantly to advancing the development of efficient micro‐scale biomimetic pumping systems tailored for precise target drug delivery applications.

Application of on-line sample preconcentration by large-volume dual preconcentration by isotachophoresis and stacking (LDIS) on straight-channel microchips.

In this study, large-volume dual preconcentration by isotachophoresis and stacking (LDIS) which is an on-line sample preconcentration technique coupling large-volume sample stacking with an electroosmotic flow pump (LVSEP) with transient isotachophoresis (tITP) was applied to microchip electrophoresis (MCE) for improving both detection sensitivities and peak shapes. To realize LDIS in MCE, we investigated experimental procedures for injecting a short plug of a leading electrolyte (LE) solution into a straight microchannel without any sophisticated injector apparatus. We found that a short LE plug could be injected into a sample-filled straight-channel only by making the liquid level of the LE solution in an outlet reservoir higher than that in an inlet one. By applying a reversed-polarity voltage to the microchip, anionic analytes injected throughout the microchannel were first enriched by LVSEP, followed by tITP. Through the second preconcentration effect by tITP in LDIS, sensitivity enhancement factor (SEF) and asymmetry factor for a standard dye were improved from 878 and 0.62 to 1330 and 1.14, respectively, relative to those in conventional LVSEP. It should be noted that more viscous running buffer containing sieving polymers could be employed to the LDIS analysis, which was effective for improving the SEF and the separation efficiencies, especially for bio-polymeric compounds. Finally, LDIS was applied to the oligosaccharide and protein analyses in MCE, resulting in the SEFs of 1410 and ca. 50 for maltotriose and bovine milk casein, respectively.

Electroosmotic flow in graphene nanochannels considering steric effects

Graphene nanochannels are excellent channels for electroosmotic flow (EOF) due to their larger slip length. In this study, the fully developed EOF in graphene nanochannels is investigated numerically, where the influence of surface charge mobility on the Navier-slip boundary conditions and the influence of steric effect on the electric potential distribution are considered. In addition, an analytical solution is provided for the scenario with low zeta potential. Detailed investigations are conducted on the impact of slip length, surface charge density, surface charge mobility, effective ion size, solution concentration, and channel height on velocity profiles. The findings indicate that the velocity increases with slip length, surface charge density, and effective ion size. Yet, accounting for surface charge mobility (αs = 0.815) leads to a reduction in slip velocity. It is noteworthy that our investigation focuses on quantifying the velocity decline due to surface charge mobility, as well as the velocity enhancement resulting from the steric effect. By adjusting parameters, such as channel height, bare slip length, and solution concentration, we achieve a maximum velocity increase of approximately 48%. These insights are valuable for optimizing the design of efficient electro-osmotic pumping systems.

Electrohydrodynamic (In)Stability of Microfluidic Channel Flows: Analytical Expressions in the Limit of Small Reynolds Number

We study electrohydrodynamic (EHD) linear (in)stability of microfluidic channel flows, i.e., the stability of interface between two shearing viscous (perfect) dielectrics exposed to an electric field in large aspect ratio microchannels. We then apply our results to particular microfluidic systems known as two-liquid electroosmotic (EO) pumps. Our novel results are detailed analytical expressions for the growth rate of two-dimensional EHD modes in Couette–Poiseuille flows in the limit of small Reynolds number (R); the expansions to both zeroth and first order in R are considered. The growth rates are complicated functions of viscosity-, height-, density-, and dielectric-constant ratio, as well as of wavenumbers and voltages. To make the results useful to experimentalists, e.g., for voltage-control EO pump operations, we also derive equations for the impending voltages of the neutral stability curves that divide stable from unstable regions in voltage–wavenumber stability diagrams. The voltage equations and the stability diagrams are given for all wavenumbers. We finally outline the flow regimes in which our first-order-R voltage corrections could potentially be experimentally measured. Our work gives insight into the coupling mechanism between electric field and shear flow in parallel-planes channel flows, correcting an analogous EHD expansion to small R from the literature. We also revisit the case of pure shear instability, when the first-order-R voltage correction equals zero, and replace the renowned instability mechanism due to viscosity stratification at small R with the mechanism due to discontinuity in the slope of the unperturbed velocity profile.

Electroosmosis of viscoelastic fluids in pH-sensitive hydrophobic microchannels: Effect of surface charge-dependent slip length

We analytically investigated the electroosmotic flow characteristics of complex viscoelastic liquids within a charged hydrophobic microchannel, considering the pH and salt concentration-dependent surface charge effects in our analysis. We examined the variation of the electric-double layer (EDL) potential field, the surface charge-dependent slip (SCDS) length, the flow field, the viscosity ratio, and both normal and shear stresses in relation to the bulk pH, bulk salt concentration, and Deborah number of the solution. Our current findings indicate that, under strong flow resistance due to increased electrical attraction on counter ions, a highly basic solution with a high EDL potential magnitude results in a significant decrease in the slip length. Neglecting the effect of SCDS leads to an overestimation of flow velocity, with this overprediction being more pronounced for highly basic solutions. This overestimation diminishes as bulk salt concentration increases, particularly when compared to strongly acidic solutions. Furthermore, a noticeable increase in average velocity is observed as the Deborah number rises for highly basic solutions compared to highly acidic ones. This is attributed to the substantial reduction in apparent viscosity caused by the shear-thinning nature of the liquid at higher shear rates, supported by a larger zeta potential modulated strong electrical force for basic solutions. Additionally, we found that the intensity of shear and normal stresses tends to increase with bulk pH, primarily due to the rise in electric body force at higher zeta potential. These results can potentially inform the design and development of a compact, nonmoving electroosmotic pump for transporting biological species with varying physiological properties, such as solution pH. This technology could be applied in subsequent processes involving mixing, separation, flow-focusing for cell sorting, and other related applications.

Sensitive detection of herbicide residues using field-amplified sample injection coupled with electrokinetic supercharging in flow-gated capillary electrophoresis.

Residues of glyphosate (GlyP) and its major degradation product, aminomethylphosphonic acid (AMPA), widely exist in the water system and plant products and thus are also present in the bodies of animals and humans. Although no solid evidence has been obtained, the concern about the cancer risk of GlyP is persistent. The measurement of GlyP and AMPA in trace levels is often needed but lacks readily available analytical approaches with detection sensitivity, accuracy and speed. This study aims to develop a simple and robust technique for the sensitive detection of GlyP and AMPA residues in a surface water system with flow-gated capillary electrophoresis (CE). Experimentally, water samples were first fluorogenically derivatized with 4-fluoro-7-nitrobenzofurazan (NBD-F) in a low-conductivity buffer at room temperature, and the mixture was injected and concentrated in the capillary based on field-amplified sample injection (FASI) coupled with electrokinetic supercharging (EKS). This scheme included a step of sample buffer injection upon electroosmotic pumping, where negatively charged analytes were electrophoretically rejected, followed by automatic voltage reversal for FASI-EKS. The detection sensitivity was improved by 296, 444, and 861 times for glufosinate (GluF), AMPA, and GlyP, respectively. The proposed method was validated in terms of accuracy, precision, limits of detection (LODs), and linearity. The LODs were estimated to be 50.0 pM, 5.0 pM, and 10.0 pM for GluF, AMPA, and GlyP, respectively. Its application was demonstrated by measuring GluF and AMPA in water samples collected from a local water system. This study provides an effective approach for the online preconcentration of negatively charged analytes, thus enabling the sensitive detection of herbicide residues in water samples. The method can also be applied to analyze other samples, including biological fluids and plant products, upon appropriate sample preparation such as solid phase extraction of analytes.

A liquid metal based, integrated parallel electroosmotic micropump cluster drive system.

The application of liquid metal in a microfluidic system enables the fabrication of highly integrated on-chip electroosmotic micropumps (EOPs). In this work, a low-voltage driveable integrated parallel EOP cluster drive system is proposed. This system consists of two layers, a branch-channel layer and a trunk-channel layer. The lower branch-channel layer contains separate parallel pumping channels and a pair of comb liquid metal electrodes. The separated branch channels are connected together through the trunk channels in the upper layer. With this structural arrangement, the parallel micropumps form an integrated micropump cluster for larger pumping capacity. The distance between the pumping channel and the electrode next to it is controlled to 20 μm. To guide the pump design, parametric studies are performed and fully discussed. According to the experimental results, the micropump cluster can be driven at a low voltage of 0.5 V, and the flow rate reaches 274 nL min-1 at 5 V. In addition, the paper finally proposes an electrode protection strategy and an integrated pump-valve drive system which is expected to solve the shortcoming of electroosmotic pumps in terms of long-time storage and driving.

Transdermal drug delivery using a porous microneedle device driven by a hydrogel electroosmotic pump.

Integrating a hydrogel electroosmotic pump with a parylene C-coated porous microneedle (PMN) is developed for transdermal drug delivery applications. The hydrogel pump is fabricated by combining an anionic and a cationic hydrogel to generate enhanced electroosmosis flow (EOF) to drive the transportation of molecules via PMN.

Multilayer track-etched membrane-based electroosmotic pump for drug delivery.

Herein, we report an electroosmotic pump (EOP) based on a multilayer track-etched polycarbonate (PC) membrane. A remarkable increase of maximum backpressure (198.2-2400mmH2 O) of a fundamental pump unit was obtained at 0.8mA, when the number of PC membranes was increased from 1 to 10. Meanwhile, the corresponding flow rate was increased from 80.3 to 111.7µL/min. Furthermore, multiple pump units were assembled in series to obtain a multistage EOP. For a three-stage EOP (EOP-3), the operating voltage and power can be decreased significantly by 52%-72% under different driving currents, with a minimum power of 26.7µW. Thus, EOP-3 can run stably over 35h at a pulse current of 0.1mA without the generation of gas bubbles. The pump was further integrated into a miniature device, which was successfully used to decrease the blood glucose level of diabetic rats by subcutaneous delivery of fast-acting insulin. This work brings a facile and efficient strategy to enhance the backpressure and lower the operating voltage and power of EOPs, which may find promising applications in drug delivery.

Fast and Strong Carbon Nanotube Yarn Artificial Muscles by Electro-osmotic Pump.

Previous electrochemically powered yarn muscles cannot be usefully operated between extreme negative and extreme positive potentials, since generated stresses during anion injection and cation injection partially cancel because they are in the same direction. We here report an ionomer-infiltrated hybrid carbon nanotube (CNT) yarn muscle that shows unipolar stress behavior in the sense that stress generation between extreme potentials is additive, resulting in an enhanced stress generation. Moreover, the stress generated by this muscle unexpectedly increases with the potential scan rate, which contradicts the fact that scan-rate-induced stress decreases for neat CNT muscles. It is revealed by the electro-osmotic pump effect that the effective ion size injected into the muscle increases with an increase in the scan rate. We demonstrate an electrochemically powered gel-elastomer-yarn muscle adhesive that generates and delivers muscle-contraction-mimicking stimulation to a target tissue.

Numerical Simulations for Electro-Osmotic Blood Flow of Magnetic Sutterby Nanofluid with Modified Darcy's Law

Owing to the considerable significance of the combination of modified law of Darcy and electric fields in biomedicine applications like drug design, and pumping of blood in heart and lung devices; so, numerical and physiological analysis on electro-osmotic peristaltic pumping of magnetic Sutterby Nanofluid is considered. Such a fluid model has not been studied before in peristaltic. The applied system of differential equations is obtained by using controls of low Reynolds number and long wavelength. Simulations for a given system are counted using two high-quality techniques, the Finite difference technique (FDM) and the Generalized Differential transform method (Generalized DTM). Vital physical parameters effects on the profiles of velocity, temperature, and Nanoparticle concentration have schemed in two different states of Sutterby fluid, the first is dilatant fluid at β<0 and Pseudo plastic fluid at β>0. A comparison between the prior results computed by FDM and Generalized-DTM and literature results are given in nearest published results have been made, and found to be excellent. The discussion puts onward a crucial observation, that the velocity of blood flow can be organized by adaptable magnetic field strength. A drug delivery system is considered one of the significant applications of such a fluid model.

A study on the thermal aging characteristics of an electro-osmotic pump using a liquid crystal polymer as a packaging material

A study on the thermal aging characteristics of an electro-osmotic pump using a liquid crystal polymer as a packaging material

Numerical Simulation and Performance Analysis of Multi-Stage Electroosmotic Micropumps

In Electro-Osmotic Pumps (EOPs), a micro fluid flow is formed by applying an external electric field via two electrodes immersed in the electrolyte. The immersed electrodes, due to lying in the fluid flow path, can consider an obstacle that can negatively affect the flow inside the microchannel. This issue is usually neglected in studies performed on the electroosmotic flows. Concerning this motivation, in this paper, a novel concept of a multi-stage EOP (introduced earlier by the researchers) was investigated numerically where the electrodes were attached to the wall of the micropump so as not to obstruct the fluid flow and to facilitate the serialization of micropumps. A two-dimensional numerical code is developed to analyze the steady-state performance of the multi-stage EOP. The governing equations for the fluid flow, internal and external electric fields, and ion concentration distribution are solved using the Finite Volume method. The results showed that in the multi-stage EOP consisting of multiple micropumps connected in series, the maximum pressure of EOP will enhances by increasing the number of micropumps. In contrast, the maximum flow rate remains approximately constant. The relationship between the maximum pressure, and the strength of the applied external electric field, was also investigated based on the electric field strength, and the results were expressed as a mathematical correlation.

Microfluidic pumps for cell sorting.

Microfluidic cell sorting has shown promising advantages over traditional bulky cell sorting equipment and has demonstrated wide-reaching applications in biological research and medical diagnostics. The most important characteristics of a microfluidic cell sorter are its throughput, ease of use, and integration of peripheral equipment onto the chip itself. In this review, we discuss the six most common methods for pumping fluid samples in microfluidic cell sorting devices, present their advantages and drawbacks, and discuss notable examples of their use. Syringe pumps are the most commonly used method for fluid actuation in microfluidic devices because they are easily accessible but they are typically too bulky for portable applications, and they may produce unfavorable flow characteristics. Peristaltic pumps, both on- and off-chip, can produce reversible flow but they suffer from pulsatile flow characteristics, which may not be preferable in many scenarios. Gravity-driven pumping, and similarly hydrostatic pumping, require no energy input but generally produce low throughputs. Centrifugal flow is used to sort cells on the basis of size or density but requires a large external rotor to produce centrifugal force. Electroosmotic pumping is appealing because of its compact size but the high voltages required for fluid flow may be incompatible with live cells. Emerging methods with potential for applications in cell sorting are also discussed. In the future, microfluidic cell sorting methods will trend toward highly integrated systems with high throughputs and low sample volume requirements.

Understanding Transient Ionic Diode Currents and Impedance Responses for Aquivion-Coated Microholes.

Ionic diode based devices or circuits can be applied, for example, in electroosmotic pumps or in desalination processes. Aquivion ionomer coated asymmetrically over a Teflon film (5 μm thickness) with a laser-drilled microhole (approximately 10 μm diameter) gives a cationic diode with a rectification ratio of typically 10-20 (measured in 0.01 M NaCl with ±0.3 V applied bias). Steady state voltammetry, chronoamperometry, and electrochemical impedance spectroscopy data are employed to characterize the ionic diode performance parameters. Next, a COMSOL 6.0 finite element model is employed to quantitatively assess/compare transient phenomena and to extract mechanistic information by comparison with experimental data. The experimental diode time constant and diode switching process associated with a distorted semicircle (with a typical diode switching frequency of 10 Hz) in the Nyquist plot are reproduced by computer simulation and rationalized in terms of microhole diffusion-migration times. Fundamental understanding and modeling of the ionic diode switching process can be exploited in the rational/optimized design of new improved devices.