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Electroosmotic pumps and their applications in microfluidic systems
Abstract
Electroosmotic pumping is receiving increasing attention in recent years owing to the rapid development in micro total analytical systems. Compared with other micropumps, electroosmotic pumps (EOPs) offer a number of advantages such as creation of constant pulse-free flows and elimination of moving parts. The flow rates and pumping pressures of EOPs matches well with micro analysis systems. The common materials and fabrication technologies make it readily integrateable with lab-on-a-chip devices. This paper reviews the recent progress on EOP fabrications and applications in order to promote the awareness of EOPs to researchers interested in using micro- and nano-fluidic devices. The pros and cons of EOPs are also discussed, which helps these researchers in designing and constructing their micro platforms.
... In the era of rapid development in aerospace engineering, micro/nano spacecrafts have widely been required on account of their inexpensive launch costs, as well as small energy dissipation and low space mission risks, to perform high-resolution measurements and complex and multifunctional assignments in the space environment [1][2][3][4][5]. The requirement has facilitated the development of micro/nano thrusters in which electro-osmosis technology is comprehensively applied, owing to enabled liquid intensive delivery, flow control, as well as mass transfer enhancement [6][7][8][9][10][11][12][13]. Electro-osmotic flow (EOF) in the thrusters is closely related to the electric double layer (EDL), which is generated by the interaction between an electrolyte solution and surface charges on the channel walls. ...
... It is noted that different values of the flow behavior index represent two kinds of non-Newtonian power-law fluids, pseudoplastic fluids (n < 1) and dilatant fluids (n > 1). If the fluid is thought of as a Newtonian fluid, the flow behavior index is equal to one (n = 1), according to Equation (11). Next, substituting Equations (1) and (11) into Equation (10), the Navier-Stokes (N-S) equation is rewritten as ...
... Specific impulse is defined as the propellant exhaust velocity divided by the gravitational acceleration constant [30,31]. The propellant exhaust velocity is regarded as the average flow velocity [10][11][12][13]. Thus, the specific impulse, I sp , is expressed as ...
In this article, electro-osmotic thrusters (EOTs), which are full of non-Newtonian power-law fluids with a flow behavior index n of the effective viscosity, are theoretically investigated in a microchannel. Different values of the flow behavior index represent two kinds of non-Newtonian power-law fluids, pseudoplastic fluids (n < 1) and dilatant fluids (n > 1), which have not yet been considered to be used as propellants in micro-thrusters. Analytical solutions of the electric potential and flow velocity are obtained using the Debye–Hückel linearization assumption and the approximate scheme of hyperbolic sine function. Then, thruster performances of power-law fluids, including specific impulse, thrust, thruster efficiency, and thrust-to-power ratio, are explored in detail. Results show that these performance curves strongly depend on the flow behavior index and electrokinetic width. It is noted that the non-Newtonian pseudoplastic fluid is most suitable as a propeller solvent in micro electro-osmotic thrusters owing to its improving or optimizing deficiencies in the performances of the existing Newtonian fluid thrusters.
... In recent years the electroosmotic flow (EOF) through nanochannels finds its widespread applications in designing lab-on-a-chip devices, which are often used in biological analysis, chemical analysis as well as industrial research and development [1][2][3][4]. When a charged surface is exposed in an electrolyte solution, a layer of immobile ions form just next to the surface and its thickness close to the diameter of ions (few angstroms). ...
... In order to scale the potential equations, we consider as the potential scale and half height of the channel is considered for the scale for coordinate. Thus, the non-dimensional form of the electric potential equations (2) may be written as (4) The non-dimensional parameter refers the Debye−Hückel parameter and is defined as ...
... But Traveling-wave induction EHD pumps has been proved effective for forced convective cooling of microelectronics benefiting from the anisotropic heating in the device environment [30]. The electroosmotic micropump, another promising non-mechanical micropump used in the microfluidic system, has been the focus of recent researches [31][32][33]. The application of direct current electroosmosis (DCEO) in microchannels has been studied theoretically and experimentally for a long time. ...
... So far, the research on ACEO flow has been carried out for more than 20 years, but in the field of electroosmosis, the research on DCEO is still the majority, and there are few reviews on the whole field of electroosmosis [32,33]. However, a lot of important research work has been carried out in the research of ACEO flow, mainly in the asymmetric electrode micropumps [36][37][41][42][43][44][45], 3D electrode micropumps [46][47][48][49][50], traveling-wave electroosmotic micropumps [38，51-53], and dc bias micropumps [31,54,55]. ...
Performance of alternating current electroosmosis (ACEO) in ethanol solutions containing three electrolytes, KOH, NH4Cl and CH3COONH4, are investigated by using asymmetric microelectrode arrays and travelling-wave microelectrode arrays in microchannels. The experiment results show that for the ACEO flow induced by the asymmetric microelectrode arrays, only the flow in the ethanol solution containing KOH is stable and the most intensive, and the flow rate can be optimized with solution conductivity 20.2μS/cm and AC frequency range from 25Hz to 125Hz. For the case by the traveling-wave microelectrode arrays, only the ACEO flow in the ethanol solution containing CH3COONH4 is stable and the most intensive, and the flow rate can be optimized with solution conductivity 30.10 μS/cm in the ac frequency range from 10 Hz to 50 Hz. Moreover, no damage occurs on the microelectrodes after useing of asymmetric microelectrodes and travelling-wave microelectrodes in the experiment.
... Electroosmosis pumping offer advantages when compared to the systems described above. They create pulse-free flows at constant temperature and may deliver virtually any amount of fluid [11]. Electroosmotic pumping is a non-mechanical pump principle based on the movement of charged areas in the liquid due to an externally applied electric field. ...
... The flow is modelled for a Newtonian fluid (water, liquid) of constant density and incompressible considering fluid flow induced by applying an electric field [11]. The charged solution is set to form close to the liquid-electrode interface, known as electric-double layer, which started to move along the pumping channel. ...
Infusion therapy is the most common form of therapy used in health care. However, the existing infusion devices show higher flow discrepancies as flow rates decrease to a few nL min ⁻¹ . As a result, dosing errors can contribute to the morbidity and mortality of patients. In the scope of project 18HLT08 MeDD II – Metrology for drug delivery, this investigation aims at the development of a silicon microchip flow pump capable of steadily and continuously dispense very low flow rates of a few nL min ⁻¹ . The fabrication methodologies explored here use a combination of typical cleanroom micro/nanofabrication techniques and off-the-shelf equipment. Preliminary tests show flow rates as low as 45 nL min ⁻¹ can be obtained in this microfluidic electroosmotic pump. The experimental flow rates are in good agreement with results predicted by multiphysics simulation, with less than 8% deviation ratio. This cost effective electroosmotic micropump has the potential to act as a steady and continuous drug delivery system to neonatal patients as well as to organs on chip (OoC), determining the stability of the shear stress imposed on the cells or the right cell culture medium conditions.
... The transport of fluids in microfluidic confinement has gained substantial attention in the recent past because of the extensive range of applications in lab-on-a-chip (LOC), micro-electromechanical systems (MEMS), biomedical and biochemical applications [1][2][3]. Among different actuation mechanisms in microscale fluid transport, research investigations on electroosmotic flow (EOF) have received the maximum attention due to its inherent features, such as pulse-free flow and elimination of moving parts. ...
... For the current work, the typical half height of the microchannel is taken as H = 10 m [6] and the fluid inside the channel is an aqueous salt solution of density = 1000 kg∕m 3 and dynamic viscosity = 0.001 Pa s [6]. Zeta potential is − 100 mV and the calculated value of dimensionless zeta potential ( ) is obtained as 4 [57]. ...
A theoretical model for entropy generation for an electroosmotic flow through a rectangular microchannel considering the finite size of ions and interfacial slip has been developed in this work to offer physical insights into the contributors of entropy generation. We use the Navier-slip model to represent interfacial slip and the modified Poisson-Boltzmann equation to describe the finite size of ions on the electric double-layer potential distribution without Debye-Huckel linearization. The modified Poisson-Boltzmann and the conservation of mass, momentum, and energy equations have been numerically solved using a finite element method-based solver. The numerical model is extensively validated with the reported experimental and numerical works. Results are presented for different viscous dissipation, Joule heating, Debye parameter, thermal Peclet number values, steric factor, and slip coefficient. It reveals that the effect of the finite size of ions on entropy generation with the consideration of interfacial slip strongly depends on the strength of the viscous and Joule heating. The average total entropy generation decreases with the slip coefficient, while it increases with the steric factor for lower values of thermal Peclet number (Pe). In contrast, the effect is opposite at higher values of Pe. For Pe = 0.1, the decrements in average total entropy generation are found as 45.25%, 38.42%, 34.89%, and 32.45%, respectively, for the steric factor of 0, 0.1, 0.2, and 0.3 with a slip coefficient of 0.
... Devices that exploit the effect are referred to as electro-osmotic pumps (EOPs). EOPs have been studied extensively for their use in a wide variety of applications such as propulsion, micro-processor cooling, lab-on-a-chip processes, and other micro-electromechanical system (MEMS) scale processes (Hansen et al., 2020;Yao, 2008;Laser and Santiago, 2004;Wang et al., 2009;Woias, 2005). Despite the diverse use of EO in EOPs, its implementation specific to acoustic projection has not been thoroughly studied. ...
... Common materials seen in EOPs are fritted glass, microcapillary arrays (MCAs), anodic alumina wafers (AAOs), MEMS fabricated channels, and polymers (Yao, 2008;Wang et al., 2009;Woias, 2005). Each EO material has its own unique properties that may make it more suitable for different applications, such as being ultra-thin, shock resistant, flexible, and so on. ...
Electro-osmosis (EO) is a non-traditional pumping and transduction mechanism with the ability to project acoustic energy in fluids. This investigation experimentally validates the influence of zeta potential, a well-studied physical characteristic used for quantifying the efficacy of an EO pump, on generation of sound pressure level. Acoustic signals of discrete frequencies were observed from 130 Hz to over 150 kHz. EO-type projectors are an attractive technology in that it does not contain moving parts, can be fabricated using a variety of materials, is intrinsically resilient to effects of hydrostatic pressure, and may be designed on the micro-electromechanical system scale.
... For example, if a 400 V electric field is applied to a cylindrical microchannel with a 1 cm length and 40 μm diameter containing an electrolyte solution (μ = 0.001 Pa.S; ζ 0 = − 0.1 V) the EOF velocity and flow rate will be 2.84 mm s − 1 and 0.85 μL min − 1 , respectively. The pressure gradient of tens or hundreds of kPa is applicable through a microchannel by varying the applied voltage (Wang et al., 2009). ...
... • Capillary electrophoresis for detecting metal ions • Versatile • High performance (Liu and Dasgupta, 1992;Wang et al., 2009) Liquid chromatography using EOF microfluidics ...
Many advanced microfluidic Lab-on-disc (LOD) devices require an on-board power supply for powering active components. LODs with an on-board electrical power supply are called electrified-LODs (eLODs) and are the subject of the present review. This survey comprises two main parts. First, we discuss the different means of delivering electrical energy to a spinning disc including slip-ring, wireless power transmission, and on-board power supply. In the second part, we focus on utilizing electrical power on eLODs for three electrokinetic microfluidic processes: electrophoresis, electroosmotic flow, and dielectrophoresis. Electrokinetic phenomena enable propulsion, separation, and manipulation of different fluids and various types of microparticles/cells. We summarize the theoretical and experimental results for all three electrokinetic phenomena enacted on centrifugal platforms. While extensive numerical modeling and experimental research are available for electrokinetics on stationary platforms, there is a noticeable lack of development in this area when executed on rotating platforms. The review concludes by comparing the strengths and weaknesses of different electrokinetic techniques implemented on centrifugal platforms, and additionally, the most promising applications of electrokinetic-assisted eLOD devices are singled out.
... When an electric field parallel to the channel axis is applied, the net force acts only on the thin charged layers near the wall, generating a pluglike velocity profile, see uðrÞ in Figure 1b. In such microfluidic settings, with non-overlapping Debye layers, electroosmosis enables in particular electroosmotic pumping [27]. In nanopores, in contrast, the channel size is often comparable to the Debye length, λ D ,R, see Figure 1c. ...
... In the last decades, this has led to a large variety of applications of EOF at the microscale such as pumps [27], micromixers [261], and transdermal drug delivery systems [262]. Some of these applications have been recently extended down to the nanoscales, such as pumps [263][264][265]. ...
Electroosmosis is a fascinating effect where liquid motion is induced by an applied electric field. Counter ions accumulate in the vicinity of charged surfaces, triggering a coupling between liquid mass transport and external electric field. In nanofluidic technologies, where surfaces play an exacerbated role, electroosmosis is thus of primary importance. Its consequences on transport properties in biological and synthetic nanopores are subtle and intricate. Thorough understanding is therefore challenging yet crucial to fully assess the mechanisms at play. Here, we review recent progress on computational techniques for the analysis of electroosmosis and discuss technological applications, in particular for nanopore sensing devices.
... Microfluidic devices are widely used in a variety of domains, ranging from drug development and diagnostics to tissue engineering and pointof-care testing [4][5][6]. Microfluidic pumps, which provide controlled fluid manipulation, play a critical role at the core of lab-on-a-chip applications [7,8]. These pumps are important in transporting samples, reagents, and analytes within microfluidic devices, allowing chemical reactions and analysis to take place. ...
Microfluidic devices have revolutionized the field of lab-on-a-chip by enabling precise manipulation of small fluid volumes for various biomedical applications. However, most existing microfluidic pumps struggle to handle high-viscosity fluids, limiting their applicability in certain areas that involve bioanalysis and on-chip sample processing. In this paper, the design and fabrication of a miniaturized Archimedean screw pump for pumping high-viscosity fluids within microfluidic channels are presented. The pump was 3D-printed and operated vertically, allowing for continuous and directional fluid pumping. The pump’s capabilities were demonstrated by successfully pumping polyethylene glycol (PEG) solutions that are over 100 times more viscous than water using a basic mini-DC motor. Efficient fluid manipulation at low voltages was achieved by the pump, making it suitable for point-of-care and field applications. The flow rates of water were characterized, and the effect of different screw pitch lengths on the flow rate was investigated. Additionally, the pump’s capacity for pumping high-viscosity fluids was demonstrated by testing it with PEG solutions of increasing viscosity. The microfluidic pump’s simple fabrication and easy operation position it as a promising candidate for lab-on-a-chip applications involving high-viscosity fluids.
... In micro/nanofluidics, AC EOF widely exists in the transportation and manipulation of fluids (Sphaier 2012;Wu & Chen 2019;Yu et al. 2023), samples (Bera & Bhattacharyya 2013;Liu et al. 2020;Wu et al. 2022) and ionic circuits (Leong et al. 2020). In the electrochemistry field, AC EOF is also broadly applied for electrochemical analysis (Wang et al. 2009), electrodeposition (Han et al. 2016;Ji et al. 2014), and soil treatment (Martin et al. 2019;Probstein & Hicks 1993). In the energy industry, AC EOF is closely associated with energy production and storage, such as the chargingdischarging cycles of supercapacitors (Agar et al. 2013;Feng & Cummings 2011) and liquid electrolyte batteries (Romanyuk et al. 2016;Wang et al. 2020), both adjacent to electrodes (Bhattacharyya & Gopmandal 2013) and the far away counterparts (Yang et al. 2015), if fast charge-discharge is required. ...
Electroosmotic flow (EOF) exists widely at the solid-liquid interface in the presence of external electric field. However, the EOF driven by an alternating current (AC) electric field in diverse chemical environments was far from being well understood due to limited experimental investigations. In this investigation, through the high-resolution laser-induced fluorescent photobleaching anemometer (LIFPA), the transient velocity according to the AC EOF on the electric double layer (EDL) far from the electrodes has been experimentally characterized, by means of time series and power spectra. With analyzing the transient velocity, the transition of AC EOF from linear to nonlinear behavior is observed in a broad parameter space, e.g. mean flow velocity, the frequency and intensity of the AC electric field, and the pH value of the bulk fluid. To take all these parameters into account, an electro-inertial velocity has been applied as the characteristic velocity, instead of the commonly applied Helmholtz-Smouluchowski velocity. Then, the transitional electric field intensity $E_{A,C}$ and the corresponding dimensionless parameter $Z_{nlc}$ are systematically studied. A power-law relationship between the linear term coefficient $Z_l$ and $Z_{nlc}$ has been established, with the scaling exponents determined by the pH value of the electrolyte solution. We hope the current investigation can provide a deeper understanding of the transition of AC EOF and the instantaneous response of EOFs in other forms. It also provides a simple model to understand the coupling between electric field and fluid flow, in both linear and nonlinear status.
... 1-Active pumping: External forces are applied to drive the flow and control the sample flow rate. In addition to the commonly used syringe and peristaltic pumps, electro-osmotic pumping is another well-known method in which ion drag is established upon application of a tangential electric field leading to a pressure gradient and thus fluid flow [118]. In another method, the digital manipulation of targeted reagents or droplets can be achieved via the utilization of forces such as acoustic [119], magnetic [120], or optical [121]. ...
Microfluidic technology is a powerful tool to enable the rapid, accurate, and on-site analysis of forensically relevant evidence on a crime scene. This review paper provides a summary on the application of this technology in various forensic investigation fields spanning from forensic serology and human identification to discriminating and analyzing diverse classes of drugs and explosives. Each aspect is further explained by providing a short summary on general forensic workflow and investigations for body fluid identification as well as through the analysis of drugs and explosives. Microfluidic technology, including fabrication methodologies, materials, and working modules, are touched upon. Finally, the current shortcomings on the implementation of the microfluidic technology in the forensic field are discussed along with the future perspectives.
... In the case of plasmonic structures, the generation of strong flows requires somehow high-temperature increments (tens of K), which can compromise their use with analytes of biomedical interest, since most of them are very sensitive to temperature variations. On the other hand, electrokinetic pumps require high electric fields for their efficient operation [28][29][30]. Moreover, both approaches require costly microfabrication techniques. ...
Efficient mixing and pumping of liquids at the microscale is a technology that is still to be optimized. The combination of an AC electric field with a small temperature gradient leads to a strong electrothermal flow that can be used for multiple purposes. Combining simulations and experiments, an analysis of the performance of electrothermal flow is provided when the temperature gradient is generated by illuminating plasmonic nanoparticles in suspension with a near-resonance laser. Fluid flow is measured by tracking the velocity of fluorescent tracer microparticles in suspension as a function of the electric field, laser power, and concentration of plasmonic particles. Among other results, a non-linear relationship is found between the velocity of the fluid and particle concentration, which is justified in terms of multiple scattering-absorption events, involving aggregates of nanoparticles, that lead to enhanced absorption when the concentration is raised. Simulations provide a description of the phenomenon that is compatible with experiments and constitute a way to understand and estimate the absorption and scattering cross-sections of both dispersed particles and/or aggregates. A comparison of experiments and simulations suggests that there is some aggregation of the gold nanoparticles by forming clusters of about 2-7 particles, but no information about their structure can be obtained without further theoretical and experimental developments. This nonlinear behavior could be useful to get very high ETP velocities by inducing some controlled aggregation of the particles.
... Fluid transport in microchannels mediated by electric potential difference is inherently advantageous over conventional mechanical pumps due to the absence of moving parts as well as its miniaturized size [14][15][16]. Apart from fluid transport, electrolyte flow over charged surface holds key importance in mimicking the flow of bio-fluid (such as plasma) in biological channels whose walls are lined with protein layer having a characteristic charge associated with them (such as negatively charged EGL) [1,17]. ...
Fluid flow characteristics under micro-confinements have been extensively explored in the past two decades. However, the flow dynamics in non-uniform micro-conduits remains relatively less explored, especially in the context of electrically actuated flows. These microscale non-uniform pathways coupled with the flow of electrolytic solutions are ubiquitous in various engineering and medical applications. Therefore, investigating the fluid flow dynamics resulting from the interplay between the degree of non-uniformity of channel geometry and electrical forcing is of utmost importance. This is beneficial not only for the fundamental understanding viewpoint but also advantageous for studies related to physiology as well as predicting the fluid rheological characteristics. Here we bring out the first report that discerns the role of channel geometry on electroosmotic flow through contracting microchannels. Our results showcase the interplay between electrical and geometrical parameters impacting the flow dynamics which would have critical implications in digital microfluidics and medical diagnostics.
... 5 Advanced electrode materials have been extensively studied for use in EO pumps. [1][2][3][4][5][6][7][8][9][10][11] Most commonly used metal electrodes such as platinum (Pt) and silver (Ag) cause critical problems, such as gas evolution, poor flow control, and metal ion release into the electrolyte. 3,12 A gas-free EO pump using Ag/Ag2O electrodes was developed by with a flow of 5 -30 ul min. ...
Ag/Ag 2 O electrodes were fabricated on both carbon fiber paper (CP) and carbon fiber cloth (CC) substrates via galvanostatic electrodeposition to develop an electroosmotic (EO) pump. The results showed that Ag was deposited along the carbon fibers and further grew into Ag particles. The Ag loading on CP was higher than that on CC at the same current density, and the difference increased further with the current density increase. Nafion coating was applied on the as-electrodeposited Ag/Ag 2 O/CP electrode to prevent the degradation of Ag particles using dip coating, followed by drop coating. The Nafion-coated Ag/Ag 2 O/CP electrodes showed much better electroosmotic pump performance and long-term stability than the uncoated electrodes, revealing that the Nafion ionomer can enhance the proton conductivity and mitigate the degradation of Ag particles during the electrochemical reactions. The EO pumps built with Nafion-modified Ag/Ag 2 O/CP electrodes with an active area of 0.28 cm ² generated a maximum pressure of 157 kPa and a maximum flow rate of 28.21 ul min. ⁻¹ . The Postmortem analysis of the pumped working fluids collected from the EO pumps operated at a constant potential for three days was performed to further investigate the effects of Nafion coating on Ag degradation.
... The alternative current (AC) EOF suppressed the water electrolysis reaction, which takes place in DC electric field and energy consumption. 24 Because of these advantages, many research groups worldwide investigate different aspects of electrokinetic phenomena in the soft channel in the AC electric field. The time-periodic EOF of an electrolyte solution through a PEL-coated nanochannel was investigated by Li et al. 25 in the applied alternating current (AC) electric field considering the Debye-H€ uckel approximation. ...
The time-dependent electroosmotic flow (EOF) and heat transfer characteristic of a generalized Maxwell fluid through the polyelectrolyte layer (PEL) grafted nanopore are investigated while considering different permittivity between the PEL and electrolyte solution. The ion partitioning effects arise due to the different permittivity among these regions. Taking the ion partitioning effects, the analytic solution for the induced potential is established within and outside the PEL from the modified Poisson–Boltzmann equation assuming the Debye–Hückel approximation for a low surface charge. The Cauchy momentum equation with a suitable constitutive equation for fractional Maxwell fluids is derived, and the corresponding analytic solution is presented to provide the axial fluid flow distribution in the full domain. The energy fluxes that have major contributions to the energy equation mainly depend on axial conduction, convection due to electrolyte transport, and Joule heating effects for the external electric field. The analytical solutions of the energy equation for hydro-dynamically fully developed flow with constant thermophysical properties are presented to provide the temperature distribution considering constant heat flux at the nanopore wall. The influence of several important factors for characterizing heat transfer behavior is investigated in the present study. The maximum fluid velocity occurs when the permittivity between the PEL and electrolyte region is the same. The increasing values of fluid velocity imply higher convective heat transfer and make the Nusselt number higher. This study makes a conscious effort toward highlighting the modality controlling the heat transfer characteristics for the ion partitioning effects.
... [1][2][3][4][5] . Burgreen and Nakache 6 and Wang et al. 7 debated the rational implications of electrokinetically driven pumping transport through microchannel. Mekheimer et al. 8 have explored the impact of electric force on blood motion through peristaltic symmetric channel and informed that the submission of electric field in the flow direction strengthens blood flow. ...
An incredible eradication of thermal indulgence is required to enhance the flow and heat transfer enhancement in micro/nanofluidic devices. In addition, the rapid transport and instantaneous mixing of colloidal suspensions of metallic particles at nanoscale are exceptionally crucial at ascendency of inertial and surface forces. To address these challenges, the present work is intended to investigate the role of trimetallic nanofluid comprising of three kinds of nano-sized granules (titanium oxide, Silica and Aluminium dioxide) with pure blood through a heated micropump in the presence of inclined magnetic field and axially implemented electric field. To ensure rapid mixing in unidirectional flow, the pump internal surface is lined-up with mimetic motile cilia with slip boundary. The embedded cilia whip in pattern due to dynein molecular motion controlled by time and produce a set of metachronal waves along the pump wall. The shooting technique is executed to compute the numerical solution. In a comparative glance it is revealed that the trimetallic nanofluid exhibits 10% higher heat transfer efficiency as compared to bi-hybrid and mono nanofluids. Moreover, the involvement of electroosmosis results in almost 17% decrease in the heat transfer rate if it values jumps from 1 to 5. The fluid temperature in case of trimetallic nanofluid is higher and thus keeps the heat transfer entropy and the total entropy lower. Furthermore, involvement of thermal radiated and momentum slip significantly contribute in reducing heat losses.
... [1][2][3][4][5] . Burgreen and Nakache 6 and Wang et al. 7 debated the rational implications of electrokinetically driven pumping transport through microchannel. Mekheimer et al. 8 have explored the impact of electric force on blood motion through peristaltic symmetric channel and informed that the submission of electric field in the flow direction strengthens blood flow. ...
... Electro-osmotic flows have been subjected to recent investigation due to their application in electro-osmotic pumps, micro-reactors, micro-energy systems and micro-electronic cooling systems [1]. In these micro-channel networks, fluid pumps are used, in which the fluid is transported by an ion-dragging effect known as electro-osmosis. ...
The in vitro fabrication of big osteoarticular implants integrating biomaterials and cells is of tremendous interest because these tissues have a limited ability to regenerate. However, the growth of such cells in vitro is highly problematic, especially later in the culture, when the extracellular matrix has almost filled the initial porous network. Thus, the fluid flow required to properly perfuse the sample cannot be obtained by the hydraulic driving force alone. Fluid pumping is a central concern of a microfluidic system and electro-osmotic pumps (EOPs) are commonly employed for this purpose. Using electro-kinetic equations as a basis, this study analyzed the variations of a two-fluid electro-osmotic flow of viscoelastic fluid flow through a channel. The behavior of the fluid was studied through the Ellis equation. This is how the electro-osmotic pump functions, as demonstrated in the literature that it electrically drags a conducting fluid across a non-conducting fluid through interfacial dragging force along the channel. A steady-state analytical solution for the system in a conducting fluid channel was studied by undertaking an interface planner for fluids exhibiting Newtonian rheological properties. The pumping characteristics were studied in detail by using the Ellis model’s parameters. The fluid rheology was studied, which showed the viability of this technique.
... On the other hand, electrokinetic pumps require high electric fields for their efficient operation. [28][29][30] Moreover, both approaches require costly microfabrication techniques. ...
Efficient mixing and pumping of liquids at the microscale is a technology that is still to be optimized. The combination of an AC electric field with a small temperature gradient leads to a strong electro-thermal flow that can be used for multiple purposes. Combining simulations and experiments, an analysis of the performance of electro-thermal flow is provided when the temperature gradient is generated by illuminating plasmonic nanoparticles in suspension with a near-resonance focused laser. Fluid flow is measured by tracking the velocity of fluorescent tracer microparticles in suspension as a function of the electric field, laser power, and concentration of plasmonic particles. Among other results, a non-linear relationship is found between the velocity of the fluid and particle concentration, which is justified in terms of multiple scattering-absorption events, involving aggregates and individual particles, that lead to enhanced absorption when the concentration is raised. Simulations provide a description of the phenomenon that is compatible with experiments and constitute a way to understand and estimate the absorption and scattering cross-sections of dispersed particles and/or aggregates. A comparison of experiments and simulations suggests that the gold nanoparticles are aggregated forming clusters of about 5-9 particles, but no information about their structure cannot be obtained without further theoretical and experimental developments. This nonlinear behavior could be useful to get very high ETP velocities by inducing some controlled aggregation of the particles.
... Micropumping is an essential function of a microfluidic system 26 . Electroosmotic micropumps are frequently utilized to perform this function, because electroosmotic micropumps possess several outstanding features: electroosmotic micropumps are capable of generating constant and pulse-free flows; the flow magnitude and direction of an electroosmotic micropumps are convenient to control; this type of micropump can be fabricated using standard microfabrication technologies and thus is readily integratable with lab-on-chip devices because of its no-moving-part characteristics 5 . Therefore, this section focuses on topology optimization of the electrodes for electroosmosis to generate the maximal flux in microchannel and achieve the micropumping performance. ...
... To avoid mixing the liquid in the pump with that in the channel by connecting the pump directly to the channel, the pump must be integrated into the channel device. Currently, pumps that do not use piezo actuators or syringes are being studied, such as electroosmotic pumps [10][11][12][13]. Glawdel et al. [14,15] used electroosmotic pumps for cell culture by creating a chip that separated the high-electric-field area from the area where cells were cultured. ...
Single-cell manipulation in microfluidic channels at the micrometer scale has recently become common. However, the current mainstream method using a syringe pump and a piezoelectric actuator is not suitable for long-term experiments. Some methods incorporate a pump mechanism into a microfluidic channel, but they are not suitable for mass production owing to their complex structures. Here, we propose a sidewall-driven micropump integrated into a microfluidic device as well as a method for reducing the pulsation of flow. This sidewall-driven micropump consists of small chambers lined up on both sides along the main flow path, with a wall separating the flow path and each chamber being deformed by air pressure. The chambers are pressurized to make the peristaltic motion of the wall possible, which generates flow in the main flow path. This pump can be created in a single layer, which allows a simplified structure to be achieved, although pulsation can occur when the pump is used alone. We created two types of chips with two micropumps placed in the flow path and attempted to reduce pulsation by driving them in different phases. The proposed dually driven micropump reduced pulsation when compared with the single pump. This device enables precise particle control and is expected to contribute to less costly and easier cell manipulation experiments.
... The pumping of liquid refers to driving it to the flow through a configurable pathway, and this mechanism largely relies on pressurizing the liquid being handled by the device/system. 1 In practical applications, pressurizing of the working liquid is accomplished by the proper actuation of mechanical components, driven by some external means.. [2][3][4] On downsizing the system length scale, equipping such mechanically moving components in small-scale systems becomes a prohibitive task and necessitating several other avenues to be explored for achieving liquid actuation mechanisms. To this end, several nature-inspired phenomena like underlying mechanism in insect respiratory system, flow of urine in kidneys, blood-sucking mechanism of mosquitoes, and flow in human physiological system such as duodenum and intestine can be deployed as novel realisms toward the development of valve-less pumping by incorporating microfluidic technology. ...
We here discuss a novel bioinspired pumping mechanism of non-Newtonian fluid in a microfluidic configuration, consistent with the propagative rhythmic contraction-expansion of a membrane attached to the wall of the fluidic channel. We consider the Rabinowitsch model to represent the rheology of non-Newtonian fluid. By employing lubrication theory and approximating the underlying flow to be in the creeping regime, the transport equations governing the pumping process are framed pertaining to the chosen set-up. The flow transport equations are then evaluated by employing well established perturbation technique. By depicting the flow velocity components, streamline patterns, and velocity contours graphically, we aptly discuss the flow structure developed in the flow pathway, and demonstrate eventual consequence of these flow parameters to the net throughput during both compression and expansion phases of the pumping process. Finally, by demonstrating a phase-space diagram, we also discuss the impact of fluid rheology and membrane kinematics on the pumping capacity. The results obtained from the proposed model establish that the net flow owing to propagative rhythmic membrane contraction strongly relies on the exponent parameter M and rheological parameter β. These consequences are expected to be of substantial practical relevance in designing micropumps intended to yield unidirectional flow of the complex fluids with improved efficiency, commonly used in biochemical/biomicrofluidic applications.
... In electroosmotic flow (EOF), the liquid moves along the charged surface by applying an external electric field tangential to the surface (Ayoubi et al., 2021;Talebi et al., 2021). A significant application of electroosmosis is fluid pumping in micro/nanofluidic systems (Wang et al., 2009). In addition, EOF has attracted the attention of researchers due to its other applications in fields such as chemical and biochemical analysis (Menestrina et al., 2014), drug delivery (Dittrich and Manz, 2006;Lavan et al., 2003;Yang et al., 2015), energy production , separation processes (Abbasi et al., 2021(Abbasi et al., , 2020Inglis et al., 2011), etc. ...
Electroosmotic flow (EOF) and ion transport through a conical nanochannel coated with polyelectrolyte layer (PEL) are numerically investigated. The diffuse character is defined by an ununiform distribution of the polymer segment density. Soft step (Type I), exponential (Type II), and sigmoidal (Type III) functions were considered to describe the charge density distribution of PEL. A nonlinear model based on the Poisson-Nernst-Planck and the Navier–Stokes equations is used. The equations were solved using the finite element method. At applied voltages of ±1V, the electroosmotic velocity within diffuse soft nanochannels follows the order of uTypeI>uTypeII>uTypeIII. The soft step function leads to more ion selectivity. Considering a charge density of 100 mol/m3 and a salt concentration of 100mM, we demonstrate that the rectification factors for the conical nanochannels, from 3 by considering the uniform PEL, can reach the value of 18 by considering the soft step function for PEL.
... Electroosmosis has been used in various fields such as highperformance liquid chromatography (HPLC) [105,106], cooling of microelectronic equipment [107], drug delivery [108][109][110], etc. In a review study, Wang, et al. studied electroosmotic pumps and their applications in microfluidic systems [111]. In another study, Chakraborty and Ray investigated the flow rate control by applying pulsed electric fields to circular microchannels using some of the intrinsic properties of the electroosmosis phenomenon [112]. ...
... Electro-osmotic flow is the movement of fluid induced by an applied potential across a capillary tube, membrane, microchannel, porous material, or any other fluid conduit. Electro-osmotic flow is commonly used in microfluidic devices having various applications in drug delivery, DNA analysis, bacteria detection, micropumps and micromixers [56,57]. The non-dimensional slip boundary conditions φ = ζ 1 at y = −1 and φ = ζ 2 at y = 1 have been chosen for this problem. ...
The study of Casson nanofluid plays a prominent role in biomedicine, magnetic resonance imaging and thermal enhancement of energy system due to the eminence of its thermophysical properties. By considering various practical applications, in this article the steady, laminar, electromagnetohydrodynamic flow of Casson nanofluid across parallel plates with the effect of Hall current, chemical reaction, modified Darcy's law and Joule heating have been taken into consideration. Gold and Silver nanoparticles of sphere shape are considered in blood taken as conventional base fluid with volume fraction of 1%. However, for comparison, other shapes of nanoparticles are also considered. The system of dimensional governing equations of nanofluid are converted to dimensionless set of equations using pertinent non-dimensional quantities. The analytical solutions are presented for the system of equations. The obtained exact solution for nanofluid velocity, nanofluid temperature, nanofluid concentration, Sherwood number, Nusselt number and shear stress are displayed graphically to see the effectiveness of sundry parameters. It is found that the velocity and temperature decreases, while concentration of Ag-blood and Au-blood rises with increased values of nanoparticle volume fraction. Performance of nanoparticle of sphere shape is lowest and lamina shape is highest in terms of heat and mass transfer. The present study may be useful in further studies of tumour therapy, biomedical imaging and cancer therapy.
... Electroosmosis is a significant study topic because of its wide applications, e.g., nanodevices in biochemical, medical, and industrial sectors [1] . An electric double layer (EDL) is formed and bonded to an exterior diffused layer inside the charged sheet. ...
The purpose of this investigation is to theoretically shed some light on the effect of the unsteady electroosmotic flow (EOF) of an incompressible fractional second-grade fluid with low-dense mixtures of two spherical nanoparticles, copper, and titanium. The flow of the hybrid nanofluid takes place through a vertical micro-channel. A fractional Cattaneo model with heat conduction is considered. For the DC-operated micropump, the Lorentz force is responsible for the pressure difference through the microchannel. The Debye-Hükel approximation is utilized to linearize the charge density. The semi-analytical solutions for the velocity and heat equations are obtained with the Laplace and finite Fourier sine transforms and their numerical inverses. In addition to the analytical procedures, a numerical algorithm based on the finite difference method is introduced for the given domain. A comparison between the two solutions is presented. The variations of the velocity heat transfer against the enhancements in the pertinent parameters are thoroughly investigated graphically. It is noticed that the fractional-order parameter provides a crucial memory effect on the fluid and temperature fields. The present work has theoretical implications for biofluid-based microfluidic transport systems.
... Direct current (DC) and alternating current (AC) EOP designs leverage the electroosmotic flow (EOF) process to achieve a laminar pulseless flow profile in a pump configuration which has no moving parts (Wang et al. 2009a(Wang et al. , 2009b. The simplicity of the EOP design makes it appealing in applications such as chromatographic separation (Chen et al. 2004) and drug delivery (Chen et al. 2007). ...
Microfluidic devices have been employed in micro-analytical systems and microelectronics using inexpensive, customisable fluid-handling automation at the microliter scale. Here we utilise a well-established fibre drawing technique, which offers a range of materials and capillary conformations, that can be utilized within microfluidic devices to control fluid movement via electroosmotic processes to produce a simple electroosmotic pump (EOP). Single capillary EOPs were fabricated from drawn PU capillary fibres with internal diameters ranging from 73 to 200 µm and were shown to be capable of actively transporting a buffer solution using an external driving electric potential. A maximum flow rate of 0.8 ± 0.1 μL/min was achieved for a 73 ± 2 µm diameter PU capillary fibre at an applied potential of 750 V/cm. This flow rate was successfully increased up to 5.3 ± 0.3 μL/min by drawing a multi-capillary array consisting of 4, 5 and 7 capillaries.
... Due to its simple construction and operation, as well as other characteristics, EOF has come to be one of the most important nonmechanical technologies in microfluids and nanofluids and is used for pumping, separating, and mixing in Microelectromechanical systems (MEMS) and Nanoelectromechanical systems (NEMS) devices [17,18]. EOF has many appliances in microfluidic liquid chromatography systems, micro flow injection analysis, micro energy systems, microelectronic cooling systems, and microreactors [19]. Scientists and researchers have become increasingly interested in electro-osmotic flow of a biological liquid through peristaltic channels in recent years [20][21][22][23][24][25]. ...
The present paper investigates the dynamic behavior of streamline patterns with their bifurcations for heat transfer in a peristaltic flow model. This model represents an incompressible Casson hybrid nanofluid Au-Cu- blood flowing through a porous saturated tapered asymmetric microchannel in the presence of electroosmotic
body force, velocity slip, and temperature jump conditions. Analytical and numerical tools are used to perform a thorough bifurcation and stability analysis of the various stagnation point positions. The global
dynamics behavior around these points generates invariant sets and attractors, such as a surface of heteroclinic connections between saddle stagnation points, which is used to predict the various flow modes and topologies that control stream flow. The impact of the physical parameters associated with flow problems,
is also thoroughly investigated and graphically illustrated.
... Therefore, a high electro-osmotic mobility liquid, such as NaCl solution, is used to drag the low electro-osmotic mobility liquid, which gives rise to a twoliquid electro-osmotic flow. 16 In fact, there are several electro-osmotic pumps consisting of two immiscible liquids with different viscosities, which find multiple applications in microelectronic cooling system, microreactors, micro energy systems, etc. 17 Ngoma and Erchiqui 16 constructed a mathematical model for the flow of two immiscible fluids in a parallel plate microchannel considering the combined effect of electro-osmosis and pressure gradient. Su et al. 18 considered semi-analytical solutions for transient electro-osmotic and pressure-driven flow of two-layer fluids in a slit microchannel and observed that the zeta potential difference at the interface of the two fluids increases the velocity amplitude. ...
We investigate the fluid flow and heat transfer characteristics for a combined electro-osmotic and pressure-driven flow of two immiscible fluids through a straight planar microchannel considering the interfacial wall slip and slip-dependent zeta potential with asymmetric wall heating. Closed-form expressions are derived for the electrical potential distribution induced in the electrical double layer (EDL), velocity, temperature, and Nusselt number of both the layers after analytically solving the Poisson–Boltzmann equation, the mass, momentum, and energy conservation equations along with suitable boundary conditions for a steady incompressible hydrodynamically and thermally fully developed flow. The results for both the layers are presented for a broad range of parameters, such as dielectric constant ratio, pressure gradient, interfacial zeta potential difference, Debye–Hückel parameter, slip length, Joule heating parameter, Brinkman number, and heat flux ratio. The flow velocity is found to attain a higher value after considering the slip effect on zeta potential for all the parameters and for both fluids, and the enhancement in the velocity is more for thinner EDL. The heat transfer characteristics for the two layers are different, where the absolute value of the Nusselt number with the slip effect on zeta potential is always higher than that for the no-slip case for the bottom layer. Contrarily, the absolute value of the Nusselt number shows an opposite trend for the upper layer. Critical values of Brinkman numbers are obtained for the bottom layer beyond which the Nusselt number is higher for thicker EDL.
... The motor mechanism is different from that of actuation of the Omnipod, which is a shape memory alloy [8]. The EOPatch uses an electroosmotic pump that allows precise automatic insulin delivery using electrochemistry, which allows a more compact size and enables correct insulin delivery capacity with less noise and heat than existing pumps [14]. EOPatch usage time is 3.5 days compared to 3 days for the Omnipod. ...
This study evaluated the safety and efficacy of tubeless patch pump called EOPatch in patients with well-controlled type 1 diabetes mellitus (T1DM). This 4-week, two-center, open-label, single-arm study enrolled 10 adult patients diagnosed with T1DM with glycosylated hemoglobin less than 7.5%. The co-primary end points were patch pump usage time for one attachment and number of serious adverse events related to the patch pump. The secondary end points were total amount of insulin injected per patch and changes in glycemic parameters including continuous glucose monitoring data compared to those at study entry. The median usage time per patch was 84.00 hours (interquartile range, 64.50 to 92.50). Serious adverse events did not occur during the trial. Four weeks later, time in range 70 to 180 mg/dL was significantly improved (70.71%±17.14 % vs. 82.96%±9.14%, P=0.01). The times spent below range (<54 mg/dL) and above range (>180 mg/dL) also improved (All P<0.05). Four-week treatment with a tubeless patch pump was safe and led to clinical improvement in glycemic control.
This study emphasizes the significance of optimizing heat transmission, energy conversion, and thermal management in electronic devices, renewable energy systems, and emerging technologies like thermoelectric devices and energy storage systems. The aim is to enhance heat transfer efficiency for improved performance and lifespan of electronic equipment. The research utilizes a mathematical flow analysis to study a water-based ternary nanofluid's flow and thermal characteristics in a vertical microfluidic channel driven by peristalsis and electroosmosis. The ternary-hybrid nanofluid (THNF), comprising copper, silver, and alumina nanoparticles dissolved in water, is examined considering induced magnetic fields. The study delves into fluid flow, heat absorption, and mixed convection, using Debye-Hückel, lubrication, and long wavelength approximations. Results show that THNF exhibits superior heat transmission compared to pure water. Increasing solid volume fraction of nanoparticles decreases THNF's temperature. Induced magnetic fields impact the system. This research could influence thermal pipe heat sinks and bioengineered medical devices design.
Molecularly rigid polymers with internal charges (positive charges induced by amine methylation) allow electroosmotic water flow to be tuned by adjusting the charge density (the degree of methylation). Here, a microporous polyamine (PIM-EA-TB) is methylated to give a molecularly rigid anion conductor. The electroosmotic drag coefficient (the number of water molecules transported per anion) is shown to increase with a lower degree of methylation. Net water transport (without charge flow) in a coupled anionic diode circuit is demonstrated based on combining low and high electroosmotic drag coefficient materials. The AC-electricity-driven net process offers water transport (or transport of other neutral species, e.g., drugs) with net zero ion transport and without driver electrode side reactions.
Unique magnetic characteristics of cobalt-ferrite nanoparticles make them suitable for biological imaging and therapeutic applications. Understanding their activity in nanofluids via the ciliary annulus could lead to better contrast agents for magnetic resonance imaging and improved cancer therapy and other medical therapies. This article provides a comprehensive analysis of the theoretical conclusions regarding the transport of a nanofluid by electroosmosis across a ciliary annulus. The nanofluid consists of cobalt-ferrite nanoparticles (CoFe2 O4 ), water (H2 O), and ethylene glycol (C2 H6 O2 ). As part of the investigation into constructing a physical model, mathematical analysis is performed based on the conservation of mass, momentum, and energy. Dimension-free analysis and mathematical constraints are utilized to learn more about the system. By generating differential equations and including suitable boundary conditions, one can obtain exact solutions, which can then be visually inspected. Recent studies have demonstrated an inverse relationship between flow velocity and cilia length, zeta potential, and Helmholtz-Smoluchowski velocity. The streamlines show that the growth of the trapping boluses is affected by several factors, including the nanoparticles' volume fraction, the cilia's length, the amplitude ratio, the eccentricity, and the zeta potential. These results not only shed light on how nanofluids move, but they also have potential applications in microfluidics, heat transfer, and biomedical engineering.
Sportswear worn next to the skin is easily soaked by sweat and may become a breeding ground for the microbiome, thus a source of malodor. Malodor can cause social embarrassment and discomfort to both wearer and others. Given the risks current deodorant products pose to nature and human life, the development of sustainable textiles for odor control comes to the forefront. This review introduces the odor-generating mechanism in clothing from the perspectives of perspiration composition and cutaneous microbiome. With the knowledge of the significant role of sweat in odor formation, the sweat distribution of the human body, measurement techniques, and advanced technologies developed for quick-dry function are presented in the second part. Lastly, odor management in sportswear is evaluated, covering the odor-assessing techniques, the effects of various textile materials, and emerging solutions in terms of antibacterial treatment, adsorbent materials, and photocatalytic degradations of odorous compounds. Overall, it is of both personal and social value to develop novel textile materials with odor-control functions by making use of natural materials and fabric designs.
We report a laser-micromachined electrolytic PCB micropump with an oil separation barrier. As advances in terms of miniaturization and performance from our previous mesoscale PCB electrolytic pump (Kim et al. in Sens Actuators A Phys 277:73–84, 2018), we employed a simple yet rapid tape-based laser-machining technique called tape-liner-supported plastic laser micromachining and pattern transfer to fabricate a microfluidic coverslip for a PCB electrode chip. Using our microfabrication technique, the coverslip is bonded to a PCB chip to form an enclosed microscale pump with a high machining precision and no need for alignment of intermediate adhesive tapes with structural layers as commonly done in previous tape-bonding work. The completed micropump demonstrated excellent pumping performance: flow rate up to 24.49 ml/min and backpressure up to 394 kPa. Electrochemical activation of electrodes consisting of a train of voltage pulses and sweeps improves the pumping performance. In order to prevent unwanted interspersion between the electrolyte and working fluid, various separation diaphragms were previously employed, but at the cost of limited working volume and flow rate as the diaphragms were permanently anchored to the pump body. Here we propose to use an oil plug as an untethered (mobile) separation barrier. After a systematic study of properties of common oils, we tested fluorinated oil (HFE-7500), hexadecane, and tetradecane as the candidate barrier materials. HFE-7500 was chosen because its interface was stable and did not degrade pumping performance for the flow-rate range of 8.47 μl/min–2.48 ml/min. We expect our micropump with the oil plug to be used as an excellent pressure source for integrated lab-on-a-chip devices, especially lab-on-a-PCBs.
Fused silica glass is a material of choice for micromechanical, microfluidic, and optical devices due to its chemical resistance, optical, electrical, and mechanical performance. Wet etching is the key method for fabricating of such microdevices. Protective mask integrity is a big challenge due extremely aggressive properties of etching solution. Here, we propose multilevel microstructures fabrication route based on fused silica deep etching through a stepped mask. First, we provide an analysis of a fused silica dissolution mechanism in buffered oxide etching (BOE) solution and calculate the main fluoride fractions like HF2-\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${HF}_{2}^{-}$$\end{document}, F-\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${F}^{-}$$\end{document}, (HF)2\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${(HF)}_{2}$$\end{document} as a function of pH and NH4F:HF ratio. Then, we experimentally investigate the influence of BOE composition (1:1–14:1) on the mask resistance, etch rate and profile isotropy during deep etching through a metal/photoresist mask. Finally, we demonstrate a high-quality multilevel over-200 μm etching process with the rate up to 3 μm/min, which could be of a great interest for advanced microdevices with flexure suspensions, inertial masses, microchannels, and through-wafer holes.
Thin electroosmotic flow (EOF) micropumps can generate flow in confined spaces such as lab-on-a-chip microsystems and implantable drug delivery devices. However, status quo methods for quantifying flow and other important parameters in EOF micropumps depend on microfluidic interconnects or fluorescent particle tracking: methods that can be complex and error-prone. Here, we present a novel connected droplet shape analysis (CDSA) technique that simplifies flow rate and zeta potential quantification in thin EOF micropumps. We also show that a pair of droplets connected by an EOF pump can function as a tunable convex lens system (TCLS). We developed a biocompatible and all polymer EOF micropump with an SU-8 substrate and poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) electrodes. We microdrilled a channel through the electrode/SU-8/electrode layers to realize a monolithic EOF micropump. Then, we deposited a pinned droplet on each end of the microchannel so that it connected them. By controlling the EOF between the droplets and measuring the corresponding change in their shape, we quantified the nanoliter EOF rate and zeta potential at the interface of SU-8 with two liquids (deionized water and a l-glutamate neurotransmitter solution). When the droplet pair and pump were used as a TCLS, CDSA successfully predicted how the focal length would change when the pump drove fluid from one droplet to another. In summary, CDSA is a simple low-cost technique for EOF rate and zeta potential measurement, and a pair of droplets connected by an EOF micropump can function as a TCLS without any moving parts.
The theoretical analysis for the mass transfer process of an oscillatory electroosmotic flow (EOF) in the fractional Jeffrey fluid model is studied through a polyelectrolyte layer (PEL) coated cylindrical annulus with reversible and irreversible wall reactions. The ion partitioning effect is observed due to the difference in permittivity of the PEL and the electrolyte solution, which is accounted for by the Born energy. Considering ion partitioning effects, analytical solutions for induced potential and axial velocity are presented, respectively in both the PEL and electrolyte region from the modified Poisson-Boltzmann equation and the Cauchy momentum equation with a proper constitutive equation, respectively. The Maxwell fluid and classical viscous Newtonian fluid models can be achieved separately by adjusting the relaxation and retardation time in the constitutive equation of this model. The analytical solution of the convection-diffusion equation for solute transport is established in the full domain. The separation of species is found to be dependent mainly on the Damköhler number, absorption parameter, phase partitioning coefficient, etc. It is observed that the osmotic pressure increases with the thickness and fixed charge density of the PEL. The velocity decreases with an increase in the permittivity difference of these layers. Our results suggest that the separation may be achieved through a difference in absorption kinetics.
The electrokinetic behaviors, including ionic current rectification (ICR), selectivity, and electroosmotic flow (EOF) of a nanopore play important role in applications such as nano sensing, salinity gradient power, and desalination of sea water. Since those behaviors can be influenced significantly by the shape and charged conditions of a nanopore, the influence of these factors on its performance is studied in detail by comparing the behavior of six types of nanopore (conical, cylindrical, cigar, funnel, hourglass, and dumbbell-shaped pores), each of them can be unipolarly or bipolarly charged. In addition to examining their performance under various conditions, the associated mechanisms are also discussed. We show that the internal volume of a nanopore is the most important factor influencing its ICR behavior. However, the selectivity of a nanopore depends both on its internal volume and the fraction of its narrow region. The bipolar and unipolar nature of a nanopore can yield interesting velocity profile, which is also influenced by the salt concentration and nanopore geometry.
In this article the peristaltic transport of Williamson fluid in a wavy microchannel has been discussed. Williamson fluid has number of applications in petroleum industry and power engineering. In order to determine the energy distribution, viscous dissipation is reckoned. Here we have considerd the wavelength of the wall motion much larger than the channel width to validate the theory of lubrication. For simplification of Poisson Boltzmann equation, we have applied the Debye-Hunkel linearization which is valid for small surface potential situations with zeta wall potential ≤25 mV. In the cases of large surface potentials, it has been found that, in comparison with the exact solution of the Poisson-Boltzmann equation, the linear solution predicts slightly lower values of the potential in the region near the wall. After a small distance from the wall, the difference between the linear solution and the exact solution diminishes. We have considered the Williamson fluid in the absence of body force. However, an external electric field has been employed. The solution of axial velocity, flow rate, pressure rise, heat transfer, mass concentration and stream functions subjected to physical partial slip boundary conditions are calculated. The effects of appropriate parameters like Debye length, Helmholtz-velocity which characterize the EDL phenomenon and external electric field are also examined. The results reveal that the peristaltic pumping varies by applying external electric field. The resulting non-linear problem has been solved analytically through the perturbation technique to analyze the distribution and change in velocity, temperature, pressure, concentration and volumetric flow rate. Results have been found through MATHEMATICA and the effects of important parameters have been discussed graphically.
Hydrogels have diverse chemical properties and can exhibit reversibly large mechanical deformations in response to external stimuli; these characteristics suggest that hydrogels are promising materials for soft robots. However, reported actuators based on hydrogels generally suffer from slow response speed and/or poor controllability due to intrinsic material limitations and electrode fabrication technologies. Here, we report a hydrogel actuator that operates at low voltages (<3 volts) with high performance (strain > 50%, energy density > 7 × 10 ⁵ joules per cubic meter, and power density > 3 × 10 ⁴ watts per cubic meter), surpassing existing hydrogel actuators and other types of electroactive soft actuators. The enhanced performance of our actuator is due to the formation of wrinkled nanomembrane electrodes that exhibit high conductivity and excellent mechanical deformation through capillary-assisted assembly of metal nanoparticles and deswelling-induced wrinkled structures. By applying an electric potential through the wrinkled nanomembrane electrodes that sandwich the hydrogel, we were able to trigger a reversible and substantial electroosmotic water flow inside a hydrogel film, which drove the controlled swelling of the hydrogel. The high energy efficiency and power density of our wrinkled nanomembrane electrode–induced actuator enabled the fabrication of an untethered insect-scale aquabot integrated with an on-board control unit demonstrating maneuverability with fast locomotion speed (1.02 body length per second), which occupies only 2% of the total mass of the robot.
Investigation concerning the bioinspired pumping flow of viscous fluids in the porous region using Darcy's law is demonstrated in the present article. The rhythmic membrane contraction propels fluids in the porous microchannel. The periodic contraction of the membrane is utilized in the present analysis to introduce the unique pumping mechanism. For small pattern, width to channel height ratio (i.e., the channel is substantially longer than its width) and at low Reynolds numbers, the governing equations are solved by an analytical approach. In light of porous effects, we noticed the implications of rheological limitations on pumping and trapping processes. The porosity has a dynamic role in the augmentation of membrane-based pumping. These outcomes may be productive in various bioengineering (drug delivery schemes) applications.
Using both analytic and numerical analyses of the Poisson–Nernst–Planck equations, we theoretically investigate the electric conductivity of a conical channel which, in accordance with recent experiments, exhibits a strong non-linear pressure dependence. This mechanosensitive diodic behavior stems from the pressure-sensitive build-up or depletion of salt in the pore. From our analytic results, we find that the optimal geometry for this diodic behavior strongly depends on the flow rate with the ideal ratio of tip-to-base-radii being equal to 0.22 at zero-flow. With increased flow, this optimal ratio becomes smaller and, simultaneously, the diodic performance becomes weaker. Consequently an optimal diode is obtained at zero-flow, which is realized by applying a pressure drop that is proportional to the applied potential and to the inverse square of the tip radius, thereby countering electro-osmotic flow. When the applied pressure deviates from this ideal pressure drop the diodic performance falls sharply, explaining the dramatic mechanosensitivity observed in experiments.
Lab-on-PCB (LoP) has been the subject of increasing research. These devices emerge as an evolution of “lab on a chip” and “PCB-MEMS”. They share interesting properties with lab-on-chip devices, for example, rapid response time and small fluid volume. In addition, lab-on-PCB devices are interesting due to the integration of electronics, sensors, actuators and microfluidics in a single platform. Besides this integration, the interest lies in the commercial availability of the Printed Circuit Boards with good dimensions and tolerances at low cost. This makes LoP devices a good choice from the market point of view. However, LoP devices are far from being robust. Unlike electronic microchips, the development of LoP devices covers many different fields (electronics, fluid mechanics, heat transfer, materials, biology, medicine, etc.) and therefore they require a multidisciplinary R&D group. In addition, LoP devices are lacking in standardization for both design and end-user interfaces.
This work is addressed to researchers and companies interested in developing biomedical devices and microdevices. In addition, this is an interesting guide for beginners to learn about Lab-on-PCB devices and PCB-MEMS.
The ion-partitioning effects on solute transport phenomena of time-periodic electro-osmotic flow in fractional Jeffrey fluid are investigated through a polyelectrolyte layer (PEL)-coated conical nanopore within a reactive wall whose ends are connected with two large reservoirs. By considering the ion-partitioning effects, analytical solutions for the induced potential and the axial velocity are presented, respectively, from the modified Poisson–Boltzmann equation and the Cauchy momentum equation with the proper constitutive equation of the fractional Jeffrey fluid model in the exterior and interior of the PEL. The analytic solution of the convection–diffusion for solute transport is established in the entire domain. The influence of the oscillating Reynolds number Re w , permittivity ratio ε r between two mediums, relaxation time [Formula: see text], retardation time [Formula: see text], phase partitioning coefficient σ p , PEL fixed charge density q fix , Debye–Hückel parameter κa, and softness parameter λ s are investigated in this study. Asymptotic solution for the axial velocity was also presented for low-oscillating Reynolds numbers and validated. The maximum axial velocity occurs when the permittivity between the PEL and electrolyte is the same for all models. The volumetric flow rate decreases with the increase in the PEL thickness, positive PEL charge density, and softness parameter in our study. The volume flow rate of the Newtonian fluid increased 24.07% for Maxwell fluid ([Formula: see text], α = 1) and 11.56% for Jeffrey fluid ([Formula: see text], α = 1, and [Formula: see text]), when [Formula: see text], Re w = 10, q fix = 5, d = 0.2, [Formula: see text], and [Formula: see text]. The mass transport rate increases with relaxation time, tidal displacement, and permittivity ratio between these layers.
Electrokinetic phenomena, especially electroosmosis in ion-selective environments, play a key role in many systems, from ion-selective nanopores to cellular processes. In this paper, the impact of ionic size on the electroosmotic flow through an ion-selective soft slit nanochannel is analytically studied. Meanwhile, the modified Poisson–Boltzmann and the modified Navier–Stokes equations were used for modeling the electrostatics and the electrohydrodynamics of the problem, respectively, and the derived equations were solved by linearizing method. The results reveal the importance of considering the effect of ionic size in the calculation, as the steric effects, especially at high charge densities of polyelectrolytes (PELs), dramatically alter both the ions arrangement and the electric potential; and amplify the electroosmotic flow. Considering Debye-Huckel parameters of 4 and 10 for the electrolyte layer and the PEL, respectively, we demonstrate that the dimensionless electroosmotic velocity in a soft nanochannel having a dimensionless soft layer thickness of 0.2, from 3.2 by ignoring the steric effect, can reach the value of 6 by considering the steric effect of ν=0.3.
Humanity is facing a water crisis due growing water demand of an increasing population, economic development, water pollution, and climate change. Ultrafiltration (UF) is a promising technology for countering the global water crisis due to its high removal potential for pathogens and turbidity at high recovery and low demand of chemicals. However, it suffers from membrane fouling and low removal performance for organic water constitutes such as natural organic matter (NOM). The selectivity for NOM increases when the pore size of the UF membrane is decreased but this also leads to reduction of permeability and energy efficiency. This problem is called the selectivity-permeability trade-off. Electrically conductive UF membranes are a new approach which might offer a solution to these problems. Most NOM are negatively charged. By application of a negative or positive electrical potential to the membrane surface, a repulsive or attractive force is induced on the charged substances in the feed water, respectively, which influences the rejection and fouling behavior of these membranes.
In this work, an ultra-thin gold coating was applied on the active and support layer of flat-sheet polymer membranes to achieve electrical conductivity. Due to the coating of both sides of the membrane, no additional counter electrode was necessary to apply an external potential. An intrinsically negatively charged polyethersulfone (PES, UP150) and an intrinsically positively charged polyamide (M5) membrane were used for electro-repulsive and electro-sorptive filtration experiments, respectively.
In the first part of this thesis, the membranes were characterized before and after the gold-coating regarding its filtration and electrochemical properties. Sputter coating only slightly changed the filtration properties of the membranes. The molecular weight cut-off was almost not affected by the gold coating. However, the pure-water permeability was reduced by 15 % and 40 % for the M5 and UP150 membrane, respectively.
In the second part of this thesis, electro-repulsive filtration was conducted with model NOM solutions and natural lake water with the UP150 membrane. At filtration of Hohloh lake water the permeability decreased by 49 % (± 2 %) when no external potential was applied (0 V). However, when negative potential was applied the permeability only decreased by 17 % (± 3 %) (at -2.5 V). The application of negative potential to the membrane active layer led to less fouling and an increased NOM rejection at cross-flow mode. The molecular weight cut-off was shifted from 150 kDa at no applied potential to 5 kDa at -2.5 V (cell potential). Therefore, it could be seen that the duplex-coated membrane configuration was almost as effective as conventional counter electrode configuration in fouling mitigating and rejection enhancement.
In the third part, electro-sorptive dead-end filtration experiments showed that the application of a positive potential led to adsorption of NOM and negatively charged organic dye molecules. When the potential was reversed to negative potential, the previously adsorbed substances could be desorbed. The process of electrosorptive UF worked with the intrinsically positively charged M5 membrane but not with the intrinsically negatively charged UP150. The molecular weight cut-off of the M5 membrane was shifted from approx. 1000 kDa at no applied potential to approx. 0.7 kDa at +2.5 V (cell potential). Therefore, the electrosorptive UF achieved a NOM rejection performance in the range of commercially available nanofiltration membranes. At the same time, the positively charged M5 membrane showed permeability in the range of loose UF membranes and fouling was not observed to be problematic. The additional energy consumption for the application of the external potential was low with 0.03 kWh/m³ of permeate.
Overall, electro-repulsive and electro-sorptive UF membranes, both, broke the selectivity-permeability trade-off of the UF process. Whereas, the electrosorptive enhancement of NOM removal was more pronounced than the electro-repulsive.
A high-performance and durable electroosmotic (EO) pump is developed using electropolymerized PANI:PSS/C electrodes. PANI:PSS was electrochemically synthesized on the carbon fiber paper using cyclic voltametry and characterized by a variety of physicochemical methods including field-emission scanning electron microscopy (FESEM), electron probe microanalyzer (EPMA), Fourier transform infrared spectroscopy (FTIR), and X-ray photoelectron spectroscopy (XPS). There was a linear relationship with a regression coefficient R2 ≥ 0.97 between the applied potential and the peak current (Ipeak), maximum flow rate (Qmax), maximum pressure (Pmax), respectively. The EO pump built with PANI:PSS/C electrodes, with an active area of 1.0 cm2, generated the maximum stall pressure of 122 kPa and the maximum flow rate of 203 ul min-1 at 4 V by using deionized (DI) water as a working fluid. The EO pumps assembled with PANI:PSS/C electrodes showed much better overall performances than those made with the bare carbon paper and exhibited good long-term stability without substantial decay for 5 days of continuous operation even at a high potential of 4 V.
The developments in microfluidics, micro-electro-mechanical systems (MEMS), and micro-total-analysis (µTAS) calls for a means to transport and mix fluid at microscale with reliability and control. Such microfluidic devices are instrumental to the realization or improvement of miniature bio/medical/chemical diagnostic kits, high performance liquid chromaographs (HPLC), fuel cells, ion exchange devices, chip and micro-circuit cooling, biochips for drug screening etc. We have developed a new technique to transport or mix fluid for micro-devices. The key concept is to exploit different polarization mechanisms and strength of the double layer at the electrode/electrolyte interface, to produce a uni-directional Maxwell force on the fluid, therefore to generate through flow pumping. By adjusting the applied electric fields, the electrode polarizations are modified. Consequently, flow direction can be manipulated simply by changing energizing electrical signals. Electroosmosis (EO) is the fluid motion induced by the movement of surface charges at the solid/liquid interface under the influence of electric fields. AC electroosmosis is implemented by applying AC electric potentials over the electrodes that are immersed in a fluid that contains ions (either an electrolyte or a dielectric liquid with ionic impurities). In AC EO, the charges in the electrical double layer are induced by the electric potentials over electrodes instead of surface charges in DC EO, and the applied potentials also provide tangential electric fields to drive the ions. Because electric fields around a symmetric electrode pair exhibit mirror symmetry, and charges in the double layer and electric fields change directions simultaneously, AC EO produces steady, counter-rotating local vortices above the electrodes [1].
Proton exchange membrane (PEM) fuel cells require humidified gases to maintain proper membrane humidification, but this often results in a problematic accumulation of liquid water. Typically, excessive air flow rates and serpentine channel designs are used to mitigate flooding at the cost of system efficiency. In this paper, we present an active water management system that decouples water removal from oxidant delivery. The system uses a porous carbon flow field plate as an integrated wick that can passively redistribute water within the fuel cell. The system also employs an external electro-osmotic (EO) pump that actively removes excess water from the channels and gas diffusion layer. For a 25 cm(2) fuel cell with 23 parallel air channels, we demonstrate a 60% increase in maximum power density over a standard graphite plate with a low air stoichiometry of 1.3. EO pumping represents a negligible parasitic load, consuming typically less than 0.5% of the fuel cell power. Experimental and modeling results show that simple passive water transport through the porous carbon alone can prevent flooding at certain operating conditions and flow field dimensions. However, active water management with EO pumping facilitates robust operation with a high volumetric power density across all operating conditions. (c) 2007 The Electrochemical Society.
An electrokinetic high pressure hydraulic pump for manipulating fluids in capillary-based systems. The pump uses electro-osmotic flow to provide a high pressure hydraulic system, having no moving mechanical parts, for pumping and/or compressing fluids, for providing valve means and means for opening and closing valves, for controlling fluid flow rate, and manipulating fluid flow generally and in capillary-based systems (Microsystems), in particular. The compact nature of the inventive high pressure hydraulic pump provides the ability to construct a micro-scale or capillary-based HPLC system that fulfills the desire for small sample quantity, low solvent consumption, improved efficiency, the ability to run samples in parallel, and field portability. Control of pressure and solvent flow rate is achieved by controlling the voltage applied to an electrokinetic pump.
Flow rates of up to 50 μm s−1 have been successfully achieved in a circular AC electro-osmotic pump. The flow rate was found to increase linearly with the applied voltage and to decrease linearly with the applied frequency. The pump is expected to be suitable for circular chromatography.
Recent years have seen considerable progress in the development of microfabricated systems for use in the chemical and biological sciences. The term micro total analytical system (µTAS) is now a well-accepted concept. Much development has been driven by a need to perform effective manipulation of chemical and biological liquids with small volumes at micro and/or nano flowrate level in these systems. In this review, the focus will be on the pumping techniques used for delivery and control of liquids, especially those physical-chemical 'continuous dynamic flow micropumps'. The principles of these pumping techniques are mainly based on one or several well-known phenomena such as electrical, light, magnetic, thermal and other actuated mechanisms. Electrokinetically-driven continuous flow pumps such as the electrophoretic pump and electroosmotic pump, surface chemistry based continuous flow micropumps such as the opto-electrowetting-based pump, optically-driven pump, electrochemical pump and constant gravity-driven pump, and combination-driven techniques such as hydrodynamic flow and electrokinetic/gravity/magnetophoretic pumping will be summarized. The focus will be on the research highlights, trends and future of these pump techniques. Finally, mixing techniques on the microscale are briefly reviewed.
We survey progress over the past 25 years in the development of microscale devices for pumping fluids. We attempt to provide both a reference for micropump researchers and a resource for those outside the field who wish to identify the best micropump for a particular application. Reciprocating displacement micropumps have been the subject of extensive research in both academia and the private sector and have been produced with a wide range of actuators, valve configurations and materials. Aperiodic displacement micropumps based on mechanisms such as localized phase change have been shown to be suitable for specialized applications. Electroosmotic micropumps exhibit favorable scaling and are promising for a variety of applications requiring high flow rates and pressures. Dynamic micropumps based on electrohydrodynamic and magnetohydrodynamic effects have also been developed. Much progress has been made, but with micropumps suitable for important applications still not available, this remains a fertile area for future research.
A programmable planar micropump for lab-on-a-chip applications has been developed. The device consists of an electroosmotic micropump combined with a mass flow sensor in a closed control loop. The micropump design with a vertical arrangement of multiple narrow polymer pumping microchannels reduces the pump area to 1/10 compared to planar micropumps with widened shallow pumping channels. This design allows the fabrication of the channel system in only one process step and is compatible with post-CMOS processing. An analytical model is presented to estimate the flow rate in a field-free pressure-driven section of the channel. It is shown that the micropump with optimized dimensions of rib structures allows high pressure low voltage pumping. The electroosmotic micropump with a suggested design using microchannels of SU-8 and polyacrylamide gel electrodes has been fabricated and tested. The pumping rate is bidirectionally linear and reaches 10 nl min−1 in a 1 cm long pressure-driven channel at an applied voltage of 40 V, which corresponds to a zero-flow pressure of 65 Pa. The micropump has been operated successfully in a closed control loop together with an on-chip mass flow sensor and external control circuitry for flow rates between 0 and 30 nl min−1.
ac electro-osmosis ACEO has emerged recently as a promising strategy for fluid transport at microscale. With an array of planar interdigital electrodes immersed in an electrolyte, different charging mechanisms at electrode/electrolyte interface and electrokinetic surface flows can be induced by nonuniform electrical fields. To implement ACEO micropump, asymmetry in an electrode pair is essential to generate net flow, which has been typically achieved through asymmetric electrode geometries. This work proposes asymmetric electrode polarization processes to break the electrode symmetry. A dc bias is superimposed onto ac potentials, so that the two electrodes in a pair undergo capacitive charging or Faradaic charging separately. Applying such signals, pumping action has been demonstrated with only a few volts of applied voltage and a power consumption in the range of milliwatts. Pumping velocity by asymmetric electrode polarization exhibits an exponential dependency on voltage. © 2008 American Institute of Physics.
This paper presents a description of the design, fabrication, and characterization of a novel, high flowrate electroosmotic pump designed for microcooling applications. The prototype pumps demonstrated a flowrate of 7 ml/min for 200 V applied potential that is suitable for two-phase heat exchangers with a capacity approaching 100 W. This pump uses electroosimotic flow (EOF) to drive the flow and is compact with no moving parts. The pump structure is produced by chemically treating and further sintering an ultrafine glass frit (filter). The frits we use are porous cylinders 30 mm in diameter and 3 mm (varying from 1.5 to 3 mm) thick and provide the high wetted-surface-to-volume ratio required to generate pressures exceeding 2 arm. Both deionized (DI) water and buffered aqueous solutions have been used as working fluids. Experiments have been conducted to characterize the pump performance and investigate its physical properties such as the structure porosity, tortuosity, effective pore size, finite double layer effects, and the dependence of zeta potential on ionic conductivity of the working solution.
Electrokinetic pumping in microporous media provides a means to integrate flow and high pressure generating capability in liTAS. A general formalism describing flow and current transport in porous media is presented. This is applied to the design of a complete electrokinetic pump-driven HPLC system that is suitable for full chip-scale integration. The application of the electrokinetic pump as a driver for mechanical actuation is also considered. A model and experimental results for the frequency response of an electrokinetic pump are presented.
A novel sequential injection analysis (SIA) method based on electrokinetic flow analysis (EKFA) system for the determination of nitrite in tap water is reported. The proposed system consists of an electroosmotic pump and two solenoid valves, all of which are controlled by a PC computer automatically. By the SIA method, accurate, reproducible and automatic determination of nitrite is achieved. The linear calibration range of nitrite-nitrogen is 0.010-0.800 mg/L. The detection limit is 1 μg/L (3σ, n = 11). The method possesses a determination frequency of 40 samples per hour.
The ability to generate high pressures using electrokinetic pumping of liquid through porous media is reported. Pressures in excess of 8000 psi have been achieved using silica capillaries packed with micron-size silica beads. A model is presented which captures absolute pressures, flowrates and power conversion efficiencies as well as the experimentally observed dependencies on pore size, applied electric field and electrical properties of the fluid. This previously unrecognized phenomena offers the possibility of creating a new class on micro- and meso-scale fluid devices where electroosmotic flow in a fine porous media is used as a pump to impart net useful hydraulic power to the fluid.
Iontophoresis enhances transdermal drug delivery by three mechanisms: (a) the ion-electric field interaction provides an additional force which drives ions through the skin; (b) flow of electric current increases permeability of skin; and (c) electroosmosis produces bulk motion of the solvent itself that carries ions or neutral species, with the solvent 'stream'. The relative importance of electroosmotic flow is the subject of this review. Experimental observations and theoretical concepts are reviewed to clarify the nature of electroosmotic flow and to define the conditions under which electroosmotic flow is an important effect in transdermal iontophoresis. Electroosmotic flow is bulk fluid flow which occurs when a voltage difference is imposed across a charged membrane. Electroosmotic flow occurs in a wide variety of membranes, is always in the same direction as flow of counterions and may either assist or hinder drug transport. Since both human skin and hairless mouse skin are negatively charged above about pH 4, counterions are positive ions and electroosmotic flow occurs from anode to cathode. Thus, anodic delivery is assisted by electroosmosis, but cathodic delivery is retarded. Water carried by ions as 'hydration water' does not contribute significantly to electroosmotic flow. Rather electroosmotic flow is caused by an electrical volume force acting on the mobile counterions. The simple 'limiting law' theory commonly given in textbooks and some research articles is a very poor approximation for transdermal systems. However, several extensions of the limiting law are compatible with each other and with the available experimental data. One of these theories, the Manning theory, has been incorporated into a theory for the effect of electroosmotic flow on iontophoresis, the latter theory being in good agreement with experiment. Both theory and experimental data indicate that electroosmotic flow increases in importance as the size of the drug ion increases. The 'ionic' or Nernst-Planck effect is the largest contributor to flux enhancement for small ions. Increased skin permeability or the skin 'damage effect', is a significant factor for both large and small ions, particularly for experiments at high current density. For monovalent ions with Stokes radii larger than about 1 nm, electroosmotic flow is the dominant flow mechanism. Because of electroosmotic flow, transdermal delivery of a large anion (or negatively charged protein) from the anode compartment can be more effective than delivery from the cathode compartment.
Low-voltage EOF pumps which consist of narrow gap channels and cascade configuration were microfabricated on quartz chips. A pressure of 500 rnmH2O (∼5000Pa) was obtained at 40V using a 120nm gap single stage pump, and it was confirmed that the pressure increase with cascade stage numbers without accumulating voltage. For an example of applications of these pumps, a linear stepping actuator was demonstrated as a pressure source of stand-alone pneumatic-driven microfluidics chips.
This work reports on the design and performance evaluation of a miniature direct methanol fuel cell (DMFC) integrated with an electroosmotic pump for methanol delivery. Electroosmotic pumps require minimal parasitic power while boasting no moving parts and simple fuel cell integration. Here, electroosmotic pumps are realized from commercially available porous glass frits. Experimental results show that electroosmotic pumps deliver 4M, and 8M methanol/water mixtures to DMFCs (at 50oC) while utilizing 1% and 4% of the fuel cells power, respectively. Furthermore, we discuss pertinent design considerations when using electroosmotic pumps with DMFCs and areas of future study.
Water management is a significant challenge in portable fuel cells and particularly in fuel cells with air-breathing cathodes. Liquid water condensation and accumulation at the cathode surface is unavoidable in a passive design operated over a wide range of ambient and load conditions. Excessive flooding of the open cathode can lead to a dramatic reduction of fuel cell power. We report a novel water management design based on a hydrophilic and electrically conductive wick in conjunction with an electroosmotic (EO) pump. A prototype air- breathing fuel cell with the proposed water management design successfully functioned under severe flooding conditions, including ambient temperature 10ºC and relative humidity 80 %, for up to 6 h without any observable cathode flooding or loss of performance.
We present experimental investigations of porous glass electroosmotic pumping of methanol/water mixture to study the feasibility of electroosmotic pump applications for direct methanol fuel cells. We first measure electroosmotic mobility of deionized water and pure methanol and evaluate pump pressure, flow rate, and current.
Electroosmotic pumps have been used in a variety of applications, typically for systems that require very low flow rates and/or pressures. The objective of this work was to develop an electroosmotic pump capable of driving a high mechanical advantage actuator that could generate large block stresses and large strains, requiring actuation pressures in excess of 0.1 MPa with flow rates on the order of 0.1 mL/s. Experiments were performed using inorganic silica and alumina membranes with different pore size. Data were obtained over a range of solution ionic strength, with results compared to model calculations developed from numerical solution of the Navier–Stokes and Poisson–Boltzmann equations. These results were used to construct a multi-stage electroosmotic pump capable of providing the desired flow rates and pressures. This multi-stage pump design was sufficiently flexible to allow adaptation to a variety of applications.
A compact high pressure hydraulic system having no moving parts for converting electric potential to hydraulic force and for manipulating fluids. Electro-osmotic flow is used to provide a valve and means to compress a fluid or gas in a capillary-based system. By electro-osmotically moving an electrolyte between a first position opening communication between a fluid inlet and outlet and a second position closing communication between the fluid inlet and outlet the system can be configured as a valve. The system can also be used to generate forces as large as 2500 psi that can be used to compress a fluid, either a liquid or a gas.
A new micro total analysis system (μTAS) designed for volumetric nanotitrations, integrating two electroosmotically driven nanopumps and a sensor unit, is presented. The unique feature of the integrated electroosmotic pumps is their ability to pump widely different solutions, independent of intrinsic characteristics such as pH or ionic strength, with the exception of viscosity. Typical flow rates achieved are in the range of 2–65nl/s, depending on the number of microchannels connected in parallel and on the applied voltage. The pulsation-free flows developed in two nanopumps push out the solutions contained in two reservoirs. The solutions are fed into a three-dimensional mixer, where the chemical reaction takes place. The potential difference as a function of the sample concentration is detected by means of a pseudo-reference electrode located in one channel and an indicator electrode placed downstream from the mixer in the sensor unit.
We present a theory for optimizing the thermodynamic efficiency of an electroosmotic (EO) pump with a large surface area highly charged nanoporous silica disk substrate. It was found that the optimum thermodynamic efficiency depends on the temperature, the silica zeta potential, the viscosity, the permittivity, the ion valency, the tortuosity of the nanoporous silica but mainly the effective normalized pore radius of the substrate scaled with respect to the Debye length. Using de-ionized water as the pumping liquid, the optimized EO pump generates a maximum flow rate of 13.6 ml/min at a pressure of 2 kPa under an applied voltage of 150 V. The power consumed by the pump is less than 0. 4 W. The EO pump was designed to eliminate any bubble in the hydraulic circuit such that the pump can be operated continuously without significant degradation in the performance.
In a typical air-breathing fuel cell design, ambient air is supplied to the cathode by natural convection and dry hydrogen is supplied to a dead-ended anode. While this design is simple and attractive for portable low-power applications, the difficulty in implementing effective and robust water management presents disadvantages. In particular, excessive flooding of the open-cathode during long-term operation can lead to a dramatic reduction of fuel cell power. To overcome this limitation, we report here on a novel air-breathing fuel cell water management design based on a hydrophilic and electrically conductive wick in conjunction with an electroosmotic (EO) pump that actively pumps water out of the wick. Transient experiments demonstrate the ability of the EO-pump to “resuscitate” the fuel cell from catastrophic flooding events, while longer term galvanostatic measurements suggest that the design can completely eliminate cathode flooding using less than 2% of fuel cell power, and lead to stable operation with higher net power performance than a control design without EO-pump. This demonstrates that active EO-pump water management, which has previously only been demonstrated in forced-convection fuel cell systems, can also be applied effectively to miniaturized (
Up to a threefold gain in sensitivity without loss of separation efficiency can be achieved by the simple expedient of connecting a larger diameter capillary at the measurement point. This is unique to electroosmotically pumped systems. Theoretical considerations are outlined and experimental verification is presented. With measurement performed by presently available commercial absorbance detectors designed for on-column detection, the gain in detectabilities can be very substantial when capillaries smaller than 75 μ m in bore are used for separation.
Electro-osmosis has been used to pump solvents in both thin-layer and high-speed liquid chromatography. The advantages of this technique over conventional methods of driving solvent are discussed.
Net flow of electrolyte induced by a traveling-wave electric potential applied to an array of microelectrodes is reported. Two fluid flow regimes have been observed: at small-voltage amplitudes the fluid flow follows the direction of the traveling wave, and at higher-voltage amplitudes the fluid flow is reversed. In both cases, the flow seems to be driven at the level of the electrodes. The experiments have been analyzed with a linear electroosmotic model based upon the Debye–Huckel theory of the double layer. The electrical problem for the experimental interdigitated electrode array is solved numerically using a truncated Fourier series. The observations at low voltages are in qualitative accordance with the electroosmotic model.
Unique properties exist in nanofluidic channels. In this paper, we report a new phenomenon, ion enrichment/depletion, associated with nanochannel structures. As a voltage is applied across a nanochannel, ions are rapidly enriched at one end and depleted at the other end of the nanochannel. The degree of this enrichment and depletion is directly related to the extent of double-layer overlap. A simple model is presented to qualitatively interpret this phenomenon.
This paper is a theoretical study of electrokinetic flow in narrow cylindrical capillaries. It is concerned with the dependence of the usual electrokinetic phenomena on the electrokinetic radius. The results obtained for this dependence must, however, be treated with caution for the higher values of the interface potential due to the use of the Debye-Hückel approximation. Of interest is the prediction of a maximum in the electroviscous effect.
A monolithic micromachined device is presented which allows on-chip adjustments of the content of organic modifier in the run buffer for fast, efficient MEKC separations. Isocratic and gradient conditions are controlled by proper setting of voltages applied to the buffer reservoirs of the microchip. The precision of this control is tested for gradients of various shapes (linear, concave, convex) by mixing pure buffer and buffer doped with a fluorescent dye. The effect of isocratic and gradient solvent changes on the MEKC separation of a mixture of coumarin dyes is demonstrated using methanol and acetonitrile as modifiers. Separations were carried out using a column length of 25 mm and a field strength of 660 V/cm with high resolution. Analysis times were as short as 33 s for methanol and under 22 s for acetonitrile. Gradients with both modifiers were executed within 10 s. Of the two modifiers, acetonitrile proved to have a more pronounced impact on the elution pattern of the test mixture. Only slight band broadening is observed for gradient runs as compared to isocratic runs using methanol. On the other hand, in the case of acetonitrile gradients, some of the peaks exhibit a focusing effect (as observed in HPLC gradients), yielding up to 100 000 plates.
The determination of nitrogen dioxide in the atmosphere has heretofore been hampered by difficulties in sample absorption and lack of specificity. A new specific reagent has been developed and demonstrated to absorb efficiently in a midget fritted bubbler at levels below 1 ppM. The reagent is a mixture of sulfanilic acid, N-(1-naphthyl)-ethylenediamine dihydrochloride, and acetic acid. A stable direct color is produced with a sensitivity of a few parts per billion for a 10-minute sample at 0.4 liter per minute. Ozone in five-fold excess and other gases in tenfold excess produce only slight interfering effects; these may be reduced further by means which are described. 25 references, 1 figure, 3 tables.
An electroosmosis based fluid propulsion system is described. The electroosmotic pump, operating in a high electric field, is isolated from other components by a grounding joint that is electrically conductive and permits the pumped fluid to be hydrodynamically coupled to contents downstream without leakage. The pump was used in single- and double-line flow injection analysis (FIA) systems. The determinations of chloride and iron(III) are discussed as representative examples. The experimental results showed excellent reproducibilities (relative standard deviation 0.4-0.8%), reflecting the stability and the reliability of the pump, The system can also be operated in a hybrid manner, On-line preconcentration (based on the electrostacking effect as used in capillary zone electrophoresis) is performed first, followed by FIA. The electrosmotically pumped fluid can be hydrostatically coupled to propel other fluids that are electrically too conductive or too resistive to be directly pumped.
Micro pumps are a critical component in micro fluidic systems. Due to its ability to generate high flow-rate/pressure without using any moving parts, electro-osmotic (EO) pumps are an appealing candidate for micro applications. As part of the effort to produce miniaturized EO pumps, macro porous silicon (PS) with high aspect ratio pores has been investigated as the pump media. Initial tests in a meso-scale pump body produced a maximum pressure of 5.2 kPa and a very large flow rate of 11.9 μl min–1 mm–2 at 60 V, demonstrating macro PS as a promising material for micro scale, high flow-rate/pressure EO pumps. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
We present experimental investigations of electroosmotic pumping using porous borosilicate glass and various low ion density liquids. The working liquids were deionized water, deuterium oxide (heavy water), methanol, acetone, acetonitrile and a 1 mM sodium borate buffer as a control. We measured ionic conductivity and, as a useful comparative reference, the zeta potential generated by these liquids in borosilicate microfluidic chips. We evaluated the electroosmotic pump performance of porous borosilicate glass structures in terms of flow rate, pressure and total ionic current. We compared experimental data to an analytical model based on numerical solutions of nonlinear Poisson–Boltzmann equation. In particular, we extend the model to the pumping of pure solvents and found a reasonable agreement with experimental results. For negligible pressure loads, pump flow rate per applied electric power can be more than ten times higher with acetone than with the 1 mM sodium borate buffer. For finite pressure loads, methanol typically yields the highest flow rate per applied electric power due to its higher pressure capacity compared to acetone. Low ion density liquids also showed strong current transients. At present, we do not have a clear understanding of the physics behind these transients, but we present measurements of current startup and discuss possible explanations for the data.