Electrokinetic Pumping Research Articles

Electro-osmotic transport and thermal energy dynamics of tetra-hybrid nano fluid in complex peristaltic flows

BackgroundThis study explores the use of tetra-hybrid nanoparticles consisting of gold, silver, alumina, and titania nanocomposites dispersed in a non-Newtonian Casson fluid modelled as blood. The motivation lies in harnessing the synergistic optical, electrical, thermal, and physicochemical properties of the multimodal nanoscale assembly to advance electrokinetic pumping processes. ObjectivesThe study aims to computationally investigate the complex transport assisted by tailored gold, silver, alumina, and titania dioxide nanoparticles in the tetra-hybrid nanofluid, with potential applications in targeted drug delivery, hyperthermia cancer treatment, Lab-on-Chip devices, and miniaturized biosensors. MethodologyThe constructed streaming flow model examines the cumulative influence of viscous heating, Joule heating, conductive thermal, and external laser irradiation. Current simulations examine Casson flows with the integrated nanoparticles by modelling two- and three-dimensional conduits subject to transverse magnetohydrodynamics and localized laser irradiation. Key findingsThe solutions provide mathematical predictions and physical insights into the fully coupled velocity, temperature, concentration, and pressure gradient contours. Additional plots examining dimensionless analytes against pertinent profiles, combined with streamlined visualization, further elucidate the multifaceted transport and complex trapping patterns stemming from non-Newtonian rheology. Applications/implicationsThis multiscale examination reveals performance improvements realizable by leveraging biocompatible tetra-hybrid nanocomposites in electrokinetic flows vital for next-generation biomedical technologies.

Charge-controlled swelling gradients at 200-µm resolution in an open-porous polymeric structure for compliance modulation

Plants combine active and passive liquid-mediated mechanisms across broad spatial and temporal scales, inspiring technological developments, in particular involving variable stiffness. Swelling is of particular interest due to the abundance of plant models and applicable (bio)materials, yet existing control by environmental humidity sorption limits its applications. This work combined swellable polymeric structures with electroactive control: we considered an open-porous polymeric laminate that hosted an electrokinetic medium also co-acting as a swelling agent for the same polymer. A constant volume of liquid (an electrolytic solution) was electrokinetically pumped between the symmetrical laminate’s interior and surface layers: as the second moment of inertia increases from the centre to the surface, the pumping of liquid towards the surface decreases the laminate’s bending stiffness, and vice versa. Ion electrosorption on high-specific-surface-area carbon electrodes, deposited in three layers in the laminate by simple additive spraying, facilitated the ion current necessary for the electrokinetic pumping. Flexural rigidity of the 400 µm thick laminate varied by 7% in response to 2-V input, evidencing swelling gradients forming at half-laminate (i.e., 200-µm) resolution. Charge-driven local rearrangement of liquid allows for broader adoption of bioinspired (and biological) porous architectures, where the channels are defined collectively, not individually as in, e.g., soft lithography. Sub-mm resolution and low-voltage control of liquid offer a high level of integration at minimal assembly, positioning active swelling as a promising solution for wearable and bioinspired soft robotic applications.

Plant-inspired rearrangement of liquid in a porous structure for controlled swelling

Soft robots can adapt to dynamic environments without prior knowledge of their properties. Plants inspire mechanisms for counterbalancing dynamic loads by locally modulating compliance through anisotropic humidity-responsive materials and structures. In addition to well-known passive bilayers, plants may also actively control swelling. The combination of robust hygroscopic material-level response and simple electrical control makes active swelling particularly attractive for technological implementation. However, dynamic swelling demands the development and optimisation of congruent pumping solutions. This work suggests electrohydrodynamic pumping, enabled by highly reversible ion immobilisation at capacitive electrodes, as a particularly suitable low-pressure, high-area liquid displacement solution for active swelling. Local pore fill ratio (PFR) modulation is used as a measure for dynamic liquid displacement and swelling. A method for highly localised (10 μm membrane thickness) assessment of the dynamic variation of PFR in a 400 μm laminate undergoing cross-plane electrokinetic liquid displacement is developed. Two modes for transient PFR modulation were identified: electrokinetic ion transfer and diffusive solvent redistribution, pronounced at high and low voltage scan rates, respectively. The strategic combination of these modes enables various compliance-modulation scenarios. The system contains (within a cycle) a constant amount of liquid in an open network of liquid-filled pores. 30%–75% PFR yielded the highest dynamic PFR modulation: a high amount of empty pores is beneficial, yet a too-low PFR compromises the continuous liquid pathway necessary for electrokinetic pumping. The dynamic nature of internal liquid rearrangement was characterised by relatively fast electrokinetics-driven fluxes (6.3% PFR change in 80 s), followed by a slow equilibration of concentration and PFR. At high scan rates, PFR decreased at positive polarisation, while both positive and negative polarity yielded a similar decrease at low scan rates (5 mV s−1). Localised control over the swelling gradient enables the design of systems that morphologically adapt to complex dynamic loading conditions.

Electrokinetic membrane pumping flow of hybrid nanofluid in a vertical microtube with heat source/sink effect

Electrokinetic membrane pumping flow of hybrid nanofluid in a vertical microtube with heat source/sink effect

Electrothermal analysis for reactive Powell Eyring nanofluid flow regulated by peristaltic pumping with mass transfer

The proposed work presents an optimized thermal frame for electroosmosis optimized peristaltic transportation of reactive Powell-Eyring magneto-nanofluid with mass transfer. The peristaltic phenomenon with the applications of electro-kinetic pumping develops the effectiveness of smart pumps in nanotechnologies and medical uses. The thermal and mass characteristics of a nanofluid is obtained by evaluating the well-known Buongiorno model, which allows us to identify appealing aspects of thermophoretic diffusion and Brownian motion. The non-Newtonian nanofluid flows through a porous space under the influence of variable thermal conductivity, chemical reactions, magnetic field, and mixed convection. Zero mass flux at the channel borders are taken. A biological estimate of the creeping transportation model, long wavelength assumptions, and Debye-Hückel linearization is revealed. The resulting equations are then resolved numerically, and the results obtained are discussed in detail along with their graphical representation. The investigation reports that electroosmotic and Joule heating parameters significantly improve the temperature of Powell Eyring nanofluid. The total entropy (irreversibility rate) of the system can be controlled with the thermal conductivity parameter in the case of auxiliary pumping. A development in concentration profile is seen for greater chemical reaction parameters. Further, nanofluid flow declines with higher values of electroosmotic velocity and the Powell-Eyring fluid parameter.

Electrokinetic insect-bioinspired membrane pumping in a high aspect ratio bio-microfluidic system

Electrokinetic insect-bioinspired membrane pumping in a high aspect ratio bio-microfluidic system

Electro-osmotic optimized flow of Prandtl nanofluid in vertical wavy channel with nonlinear thermal radiation and slip effects

The simulations have been performed for the nonlinear radiative flow of Prandtl nanofluid following the peristaltic pumping in a wavy channel. The applications of entropy generation for the electrokinetic pumping phenomenon are also focused as a novelty. The complex wavy channel induced the flow of Prandtl nanofluid. Moreover, the formulated problem is solved by using the convective thermal and concentration boundary conditions. The Keller Box numerical procedure is adopted as a tool for the simulation task. The results are also verified by implementing the built-in numerical technique bvp4c. The comparison tasked against obtained numerical measurement has been done with already reported results with excellent manner. The physical characteristics based on the flow parameters for velocity, heat transfer phenomenon, concentration field, and entropy generation pattern is visualized graphically. It has been observed that the presence of thermal slip and concentration enhanced the heat transfer rate and concentration profile, respectively. The skin friction coefficient declines with electro-osmotic force and slip parameter. The increasing variation in Nusselt number is observed for electro-osmotic parameter for both linear and non-linear radiative phenomenon.

Electro-osmosis-modulated biologically inspired flow of solid–liquid suspension in a channel with complex progressive wave: application of targeted drugging

Electrokinetic microperistaltic pumps are important biomechanical devices that help target drug delivery to specific body parts. The current study focuses on the mathematical modelling and analysis of some important aspects of such flows in a channel with complex waves. It is considered that solid particles are uniformly distributed in the flow, and that these particles are non-conducting. Parameters such as the particle volume fraction coefficient, electro-osmotic parameter, and Helmholtz–Smoluchowski parameter are specifically focused on in this study. Equally sized spherical particles were uniformly floated in a non-Newtonian Powell–Eyring base fluid. The defined flow problem was modelled and analyzed analytically for the transport of a solid–liquid suspension. It is accepted that the flow is steady, non-turbulent, and propagating waves have a considerably longer wavelength compared to the amplitude. The conditions and assumptions lead to a model of the coupled partial differential equations of order two. The exact results of the homotopy perturbation method expansion method are obtained and shown accordingly. Predictions of the behavior of important parameters are displayed in the figures. The impact of several parameters was analyzed. The current study involved transporting or targeted drug delivery systems using peristaltic micropumps and magnetic fields in the pharmacological engineering of biofluids, such as blood.

Entropy generation analysis in the electro-osmosis-modulated peristaltic flow of Eyring–Powell fluid

In the current paper, numerical study is carried out to investigate the peristaltic propulsion of Eyring–Powell fluid in a vertical symmetric channel with electro-kinetic pumping and transvers Lorentz force. The mass, momentum and energy equations for non-Newtonian fluid are formulated and simplified using suitable transformations and dimensionless variables. The governing equations in dimensionless form are solved numerically by implicit finite difference scheme for stream function and temperature profile in computational software Mathematica 9. The impact of several parameters of interest is analyzed and discussed for both values of Helmholtz–Smoluchowski velocity UHS and Joule heating parameter through graphs. An entropy generation analysis is also considered and observed for various values of involved parameters. The nonlinear dimensionless equations are also solved by another numerical technique which is built in routine in MATLAB which is commonly known as bvp4c. The results for velocity and temperature are compared by both techniques. The Joule heating parameter also increases the size and number of isothermal bolus. The entropy of the system can be controlled for assisting pumping, i.e., UHS 0.

Electroosmotic flow: From microfluidics to nanofluidics.

Electroosmotic flow (EOF), a consequence of an imposed electric field onto an electrolyte solution in the tangential direction of a charged surface, has emerged as an important phenomenon in electrokinetic transport at the micro/nanoscale. Because of their ability to efficiently pump liquids in miniaturized systems without incorporating any mechanical parts, electroosmotic methods for fluid pumping have been adopted in versatile applications—from biotechnology to environmental science. To understand the electrokinetic pumping mechanism, it is crucial to identify the role of an ionically polarized layer, the so‐called electrical double layer (EDL), which forms in the vicinity of a charged solid–liquid interface, as well as the characteristic length scale of the conducting media. Therefore, in this tutorial review, we summarize the development of electrical double layer models from a historical point of view to elucidate the interplay and configuration of water molecules and ions in the vicinity of a solid–liquid interface. Moreover, we discuss the physicochemical phenomena owing to the interaction of electrical double layer when the characteristic length of the conducting media is decreased from the microscale to the nanoscale. Finally, we highlight the pioneering studies and the most recent works on electro osmotic flow devoted to both theoretical and experimental aspects.

Electrokinetic membrane pumping flow model in a microchannel

A microfluidic pumping flow model driven by electro-osmosis mechanisms is developed to analyze the flow characteristics of aqueous electrolytes. The pumping model is designed based on a single propagative rhythmic membrane contraction applied on the upper wall of a microchannel. The flow lubrication theory coupled with a nonlinear Poisson–Boltzmann equation is used to model the microchannel unsteady creeping flow and to describe the distribution of the electric potential across the electric double layer. A generic solution is obtained for the Poisson–Boltzmann equation without the Debye–Hückel linearization. The effects of zeta potential, Debye length, and electric field on the potential distribution, pressure distribution, velocity profiles, shear stress, and net flow rate are computed and interpreted in detail. The results have shown that this electrokinetic membrane pumping model can be used to understand microlevel transport phenomena in various physiological systems. The proposed model can also be integrated with other microfluidic devices for moving microvolume of liquids in artificial capillaries used in modern biomedical applications.

Thermokinetic transport of dilatant/pseudoplastic fluids in a hydrophobic patterned micro-slit

The flow enhancement and convective heat transfer along with entropy generation analysis are studied numerically in a micro-slit with alternating hydrodynamic slip patches. The advances in molecular simulations and micro-scale experiments confirmed that the slip of fluid on the solid surfaces occurred at small scale flows and the traditional no-slip boundary conditions cannot be applicable for the flow simulation at the micro- and nano-scale. The coupled Poisson–Boltzmann–Navier–Stokes equations dealing with an external electric potential are involved for the flow enhancement and entropy generation analysis of non-Newtonian fluids in a micro-slit with periodic slips. From the finite volume simulation, it is observed that the drag force effect is very strong along the wall for the transportation and mixing of fluids. This effect is found to be minimized by imposing periodic hydrophobic slippage along the boundary. An additional pressure gradient is generated by imposing electrokinetic pumping, resulting in a higher velocity gradient in the flow direction in the presence of viscous dissipation and Joule heating effects. The results are predicted in terms of the flow enhancement factor (Ef) (which provides maximum species transport), the average heat transfer rate (Nu), and the average entropy generation due to fluid friction, heat transfer, and Joule heating effects. The advantages and disadvantages of utilizing slip conditions are discussed, which has large scale applications on drug delivery and DNA analysis and sequencing, since cell damage due to pumping will be minimized.

Scalable Parallel Manipulation of Single Cells Using Micronozzle Array Integrated with Bidirectional Electrokinetic Pumps.

High throughput reconstruction of in vivo cellular environments allows for efficient investigation of cellular functions. If one-side-open multi-channel microdevices are integrated with micropumps, the devices will achieve higher throughput in the manipulation of single cells while maintaining flexibility and open accessibility. This paper reports on the integration of a polydimethylsiloxane (PDMS) micronozzle array and bidirectional electrokinetic pumps driven by DC-biased AC voltages. Pt/Ti and indium tin oxide (ITO) electrodes were used to study the effect of DC bias and peak-to-peak voltage and electrodes in a low conductivity isotonic solution. The flow was bidirectionally controlled by changing the DC bias. A pump integrated with a micronozzle array was used to transport single HeLa cells into nozzle holes. The application of DC-biased AC voltage (100 kHz, 10 Vpp, and VDC: −4 V) provided a sufficient electroosmotic flow outside the nozzle array. This integration method of nozzle and pumps is anticipated to be a standard integration method. The operating conditions of DC-biased AC electrokinetic pumps in a biological buffer was clarified and found useful for cell manipulation.

Analysis of entropy generation in biomimetic electroosmotic nanofluid pumping through a curved channel with joule dissipation

Biomimetic designs are increasingly filtering into new areas of technology in recent years. Such systems exploit characteristics intrinsic to nature to achieve enhanced adaptivity and efficiency in engineering applications. Peristaltic propulsion is an example of such characteristics and in the current article it is explored as a feasible mechanism for deployment in electrokinetic pumping of nanofluids through a curved distensible conduit as a model for a bioinspired smart device. The unsteady mass, momentum, energy and nanoparticle concentration conservation equations for a Newtonian aqueous ionic fluid under an axial electrical field are formulated and simplified using lubrication approximations and low zeta potential (Debye Hückel linearization). A dilute nanofluid is assumed with Brownian motion and thermophoretic body forces present. The reduced non-dimensional conservation equations are solved with the symbolic software, Mathematica 9 via the NDSolve algorithm for velocity, temperature, nano-particle concentration distributions for low zeta potential. An entropy generation analysis is also conducted. The influence of curvature parameter, maximum electroosmotic velocity (Helmholtz-Smoluchowski velocity), inverse EDL thickness parameter, zeta potential ratio and Joule heating parameter on transport characteristics is evaluated with the aid of graphs and contour plots. Temperature profiles are elevated with positive Joule heating and reduced with negative Joule heating whereas the opposite behaviour is observed for the nano-particle concentrations.

Electrokinetic flow in the U-shaped micro-nanochannels

U-shaped micro-nanochannels can generate significant flow disturbance as well as locally amplified electric field, which gives itself potential to be microfluidic mixers, electrokinetic pumps, and even cell lysis process. Numerical simulation is utilized in this work to study the hidden characteristics of the U-shaped micro-nanochannel system, and the effects of key controlling parameters (the external voltage and pressure) on the device output metrics (current, maximum values of electric field, shear stress and flow velocity) were evaluated. A large portion of current flowing through the whole system goes through the nanochannels, rather than the middle part of the microchannel, with its value increasing linearly with the increase of voltage. Due to the local ion depletion near micro-nanofluidic junction, significantly enhanced electric field (as much as 15 fold at V=1 V and P0=0) as well as strong shear stress (leading to electrokinetic flow) is generated. With increasing external pressure, both electric field and shear stress can be increased initially (due to shortening of depletion region length), but are suppressed eventually at higher pressure due to the destruction of ion depletion layer. Insights gained from this study could be useful for designing nonlinear electrokinetic pumps and other systems.

Soil vapor extraction of wet gasoline-contaminated soil made possible by electroosmotic dewatering\u2013lab simulations applied at a field site

PurposeSoil restoration is still mainly carried out ex situ by excavating and replacing the contaminated soil. In situ remediation would reduce the costs of soil transportation and this way, the problem is not merely transferred elsewhere. The present study introduces a field case where the aged, oil-contaminated soil in a former fuel station in Finland was treated in situ sequentially with different methods.Materials and methodsSeveral approaches, including soil vapor extraction and biostimulation with electrokinetic pumping, were performed in the field. After these treatments, the dense original portion of the soil beneath the gasoline pump location, ca 100 m3, was still contaminated with petroleum-derived volatile organic compounds (VOCs), with concentrations of nearly 10,000 mg kg−1 measured at some hotspots. After a period of electroosmotic water circulation, the electrical field (0.5 V cm−1, DC) was kept connected for 6 months without addition of water, leading to dewatering and warming of the soil.Results and discussionIn contrast to the situation with the original wet soil, VOCs, in lab conditions, were found to volatilize very efficiently from the dewatered soil. When the soil vapor extraction treatment was renewed using perforated tubing installed horizontally at ca 1 m depth in the dewatered soil at the contaminated site, the treatment was efficient and the soil was decontaminated in 5 months. The final VOC concentrations were on average 190 mg kg−1 (n = 13) with the highest value of 700 mg kg−1 at one hotspot. After a risk evaluation, the site was concluded to be sufficiently clean for industrial use.ConclusionsSince with many former fuel stations, the contamination consists of both volatile fractions that are difficult to degrade by biological means and heavier compounds for which biostimulation is often suitable, a combination of different methods may be worth pursuing.

Electrothermal transport of nanofluids via peristaltic pumping in a finite micro-channel: Effects of Joule heating and Helmholtz-Smoluchowski velocity

The present article studies theoretically the electrokinetic pumping of nanofluids with heat and mass transfer in a micro-channel under peristaltic waves, a topic of some interest in medical nano-scale electro-osmotic devices. The microchannel walls are deformable and transmit periodic waves. The Chakraborty-Roy nanofluid electrokinetic formulation is adopted in which Joule heating effects are incorporated. Soret and Dufour cross-diffusion effects are also considered. Under low Reynolds number (negligible inertial effects), long wavelength and Debye linearization approximations, the governing partial differential equations for mass, momentum, energy and solute concentration conservation are derived with appropriate boundary conditions at the micro-channel walls. The merging model features a number of important thermo-physical, electrical and nanoscale parameter, namely thermal and solutal Grashof numbers, the Helmholtz-Smoluchowski velocity (maximum electro-osmotic velocity) and Joule heating to surface heat flux ratio. Closed-form solutions are derived for the solute concentration, temperature, axial velocity, averaged volumetric flow rate, pressure difference across one wavelength, and stream function distribution in the wave frame. Additionally expressions are presented for the surface shear stress function at the wall (skin friction coefficient), wall heat transfer rate (Nusselt number) and wall solute mass transfer rate (Sherwood number). The influence of selected parameters on these flow variables is studied with the aid of graphs. Bolus formation is also visualized and analyzed in detail.

Challenges in realizing a self-contained hydraulically-driven contractile fiber actuator.

The field of soft robots would benefit from electrically controlled contractile actuators in the form of fibers that achieve a strain of 20% in less than a second while exerting high force. This work explores possible designs for achieving this goal using self-contained electroosmotic fluid pumping within a tube-shaped structure. The most promising configuration is a combination of a bellows and a McKibben-type muscle, since pumping fluid from the former to the latter results in contraction of both portions. Realizing such a device entails challenges in fabrication and electrokinetic fluid pumping in closed systems. Further studies of electroosmotic flow in salt-free organic solvents are needed.

Multiplexed immunosensing and kinetics monitoring in nanofluidic devices with highly enhanced target capture efficiency

Nanofluidic devices promise high reaction efficiency and fast kinetic responses due to the spatial constriction of transported biomolecules with confined molecular diffusion. However, parallel detection of multiple biomolecules, particularly proteins, in highly confined space remains challenging. This study integrates extended nanofluidics with embedded protein microarray to achieve multiplexed real-time biosensing and kinetics monitoring. Implementation of embedded standard-sized antibody microarray is attained by epoxy-silane surface modification and a room-temperature low-aspect-ratio bonding technique. An effective sample transport is achieved by electrokinetic pumping via electroosmotic flow. Through the nanoslit-based spatial confinement, the antigen-antibody binding reaction is enhanced with ∼100% efficiency and may be directly observed with fluorescence microscopy without the requirement of intermediate washing steps. The image-based data provide numerous spatially distributed reaction kinetic curves and are collectively modeled using a simple one-dimensional convection-reaction model. This study represents an integrated nanofluidic solution for real-time multiplexed immunosensing and kinetics monitoring, starting from device fabrication, protein immobilization, device bonding, sample transport, to data analysis at Péclet number less than 1.

Bubble‐free electrokinetic flow with propylene carbonate

For electroosmotic pumping, a large direct-current (DC) electric field (10+ V/cm) is applied across a liquid, typically an aqueous electrolyte. At these high voltages, water undergoes electrolysis to form hydrogen and oxygen, generating bubbles that can block the electrodes, cause pressure fluctuations, and lead to pump failure. The requirement to manage these gases constrains system designs. This article presents an alternative polar liquid for DC electrokinetic pumping, propylene carbonate (PC), which remains free of bubbles up to at least 10 kV/cm. This offers the opportunity to create electrokinetic devices in closed configurations, which we demonstrate with a fully sealed microfluidic hydraulic actuator. Furthermore, the electroosmotic velocity of PC is similar to that of water in PDMS microchannels. Thus, water could be substituted by PC in existing electroosmotic pumps.