Presence Of Electric Double Layer Research Articles

Anomalous Adsorption of PFAS at the Thin‐Water‐Film Air‐Water Interface in Water‐Unsaturated Porous Media

AbstractPer‐ and poly‐fluoroalkyl substances (PFAS) are interfacially‐active contaminants that adsorb at air‐water interfaces (AWIs). Water‐unsaturated soils have abundant AWIs, which generally consist of two types: one is associated with the pendular rings of water between soil grains (i.e., bulk AWI) and the other arises from the thin water films covering the soil grains. To date, the two types of AWIs have been treated the same when modeling PFAS retention in vadose zones. However, the presence of electrical double layers of soil grain surfaces and the subsequently modified chemical potential of PFAS at the AWI may significantly change the PFAS adsorption at the thin‐water‐film AWI relative to that at the bulk AWI. Given that thin water films contribute to over 90% of AWIs in the vadose zone under many field‐relevant wetting conditions, it is critical to quantify the potential anomalous adsorption of PFAS at the thin‐water‐film AWI. We develop a thermodynamic‐based mathematical model to quantify this anomalous adsorption. The model couples the chemical equilibrium of PFAS with the Poisson‐Boltzmann equation that governs the distribution of electrical potential in a thin water film. Our model analyses suggest that PFAS adsorption at thin‐water‐film AWI can deviate significantly (up to 82%) from that at bulk AWIs. The deviation increases for lower porewater ionic strength, thinner water film, and higher soil grain surface charge. These results highlight the importance of accounting for the anomalous adsorption of PFAS at the thin‐water‐film AWI when modeling PFAS fate and transport in the vadose zone.

Fully developed opposing mixed convection in inclined microchannel with electric double layer effects

In this paper, the mixed convection flow driven in an inclined microchannel by pressure gradient and buoyancy in the presence of electrical double layer is considered. Analytical solutions for electrostatic potential, velocity and temperature distribution are given to the governing equations ruled by the buoyancy parameter, the pressure parameter, and the electrostatic and stream potential parameters after dimensionless transformation. The influences of various physical parameters on velocity and temperature distribution are illustrated and discussed. The onset of flow reversal is examined in detail. In addition to the pressure gradient and buoyancy, it is found that the electrostatic force is significant to affect the flow reversal regime, and the thickness of the electrical double layer has little effect on it. It is also found that the stream potential increases with zeta potential and the thickness of electrical double layer.

Electrokinetics of polymeric fluids in narrow rectangular confinements.

The flow of polymeric liquids in narrow confinements with a rectangular cross section, in the presence of electrical double layers is analyzed here. Our analysis is motivated by the fact that many of the previous studies on the flow of complex fluids tend to focus on highly idealized parallel plate channels, which are markedly different from the rectangular ducts, used in many experiments and devices. We consider the combined electroosmotic and pressure driven flows as well as the streaming potential resulting from a mechanically driven flow. We use two distinct constitutive relations to model the polymeric liquids, namely the simplified exponential Phan-Thien-Tanner (sePTT) model and the Giesekus model, both of which are non-linear viscoelastic models, capable of capturing the shear thinning behavior. We establish that the applied electric field may have a strong influence on the overall flow rate, which rapidly increases with the field strength as well as the extent of viscoelasticity of the fluid. Viscoelasticity and shear thinning behavior also enhance the streaming potential by several fold as compared to a Newtonian medium. We demonstrate that the aspect ratio of a channel has a bigger influence on the net throughput and the streaming potential, when the extent of viscoelasticity is relatively large. We illustrate that for sePTT fluids, the flow is strictly unidirectional, while for Giesekus fluids, secondary flows are inevitably present on account of their non-zero second normal stress coefficient. Although the electric field does not change the overall patterns of these secondary flows, their magnitude does depend on the imposed field strength for combined flows.

Forced convection with unsteady pulsating flow of a hybrid nanofluid in a microchannel in the presence of EDL, magnetic and thermal radiation effects

An unsteady force convection flow of a hybrid nanofluid flow driven in a microchannel by an applied time-dependent periodic pressure gradient in the presence of electric double layer, magnetic field, and thermal radiation effects is studied. Few attentions have been paid to investigate such pressure driven flow in micro-scale though they could be very important in practical applications. In our configuration, the Boltzmenn-Poisson's equation is employed to describe the electrostatic potential, while the reduced Navier-stokes equations based on small pressure amplitude assumption are applied to depict the conservations of momentum and thermal energy. Analytical solutions for all fields are obtained. The influences of physical parameters such as the Debye-Hückel parameter, the Hartmann number, the angular velocity, and the thermal radiation parameter on both steady and unsteady components of the velocity and temperature profiles are presented and discussed. Results show that hybrid nanofluids hold almost the same behaviours as conventional nanofluids. Therefore it is expected to replace conventional nanofluids by hybrid nanofluids for design of cheaper and higher performance heat exchangers or cooling systems and so on.

Theoretical analysis of non-Newtonian blood flow in a microchannel

Background: In this work the theoretical analysis is presented for a electroosmotic flow of Bingham nanofluid induced by applied electrostatic potential. The linearized Poisson-Boltzmann equation is considered in the presence of Electric double layer (EDL). A Bingham fluid model is employed to describe the rheological behavior of the non-Newtonian fluid. Mathematical formulation is presented under the assumption of long wavelength and small Reynolds number. Flow characteristics are investigated by employing Debye-Huckel linearization principle. Such preferences have not been reported previously for non-Newtonian Bingham nanofluid to the best of author’s knowledge.Method: The transformed equations for electroosmotic flow are solved to seek values for the nanofluid velocity, concentration and temperature along the channel length.Results: The effects of key parameters like Brinkmann number, Prandtl number, Debey Huckel parameter, thermophoresis parameter, Brownian motion parameter are plotted on velocity, temperature and concentration profiles. Graphical results for the flow phenomenon are discussed briefly.Conclusions: Non-uniformity in channel as well as yield stress τ0 cause velocity declaration for both positive and negative values of U. Nanofluid temperature is found an increasing function of electro osmotic parameter κ if U is positive while it is a decreasing function if U is negative. A completely reverse response is seen in case of concentration profile. The thermophoresis parameter Nt, the Brow nian motion parameter Nb and Brinkman number Br cause an enhancement in temperature. The results are new in case of U.

Influence of electric fields on metal self-diffusion barriers and its consequences on dendrite growth in batteries.

Based on the results of periodic density functional theory calculations, we have recently proposed that the height of self-diffusion barriers can serve as a descriptor for dendrite growth in batteries [M. Jäckle et al., Energy Environ. Sci. 11, 3400 (2018)]. However, in the determination of the self-diffusion barriers, the electrochemical environment has not been taken into account. Still, due to the presence of electrical double layers at electrode/electrolyte interfaces, strong electric fields can be present close to the interfacial region. In a first step toward including the electrochemical environment, we have calculated barriers for terrace-diffusion on lithium, magnesium, and silver surfaces and across-step self-diffusion on lithium in the presence of electric fields. Whereas the electric field effect is more pronounced on a stepped surface than on flat terraces, overall we find a negligible influence of electric fields on self-diffusion barriers which we explain by the good screening properties of metals.

Study of electrokinetic effects for heat transfer in microchannel with sinusoidal thermal boundary conditions

PurposeThe purpose of this study is to obtain the numerical as well as regularity results for the nonlinear elliptic set of equations arising in the study of fluid flow in microchannel induced by the pressure in the presence of interfacial electrokinetic effects.Design/methodology/approachFor the numerical study, the authors implemented traditional FDM approach, and for the regularity results they used the classical energy estimates. The interfacial electrokinetic effects result in an additional source term in classical momentum equation, hence affecting the characteristics of the flow and heat transfer. The sinusoidal temperature variation is assumed on side walls.FindingsThe results were obtained for various combinations of physical parameters appearing in the governing equations. This study concludes that in the presence of electric double layer, the average heat transfer rate reduces along with larger values of Reynolds number. It is observed that the heat transfer increases with the increase in amplitude ratio and phase deviation. The flow behavior and heat transfer rate inside the microchannel are also strongly affected by the presence of κ (kappa).Originality/valueTo the best of the authors’ knowledge, the problem of heat transfer through microchannel in combination with sinusoidal temperature variation at boundary with electric double layer effects has not been considered previously. Hence, this paper focuses on the influence of the sinusoidal boundary temperature distributions on both sidewalls of a rectangular microchannel through parallel plates with electrokinetic effects on the pressure-driven laminar flow. In addition, a detailed mathematical analysis is also to be carried out to verify the regularity of this model with the proposed boundary conditions. The study used the classical energy method to get the regularity results.

Understanding the Effect of Tungsten on Corrosion Behavior of AlCuCrFeMnWx High-Entropy Alloys in 3.5 wt.% NaCl Solution

The electrochemical study of AlCuCrFeMnWx (x = 0, 0.05, 0.1, 0.5, 1 mol) high-entropy alloys (HEA) is performed in 3.5 wt.% NaCl solution at room temperature (25 °C). The potentiodynamic polarization curve of the AlCuCrFeMnWx (x = 0, 0.05, 0.1, 0.5, 1 mol) alloys obtained in 3.5 wt.% NaCl solution shows that the corrosion resistance of the tungsten (W)-free HEA is lower than the alloys containing W. It is observed that W forms solid WO3 layer in the outer region of the film in a 3.5 wt.% NaCl. The scanning electron microscopy and infrared spectroscopy confirmed the electrochemical results. The electrochemical impedance spectroscopy of these alloys had one capacitive loop, which represented the presence of electrical double layer.

Analysis of Mixed Convection in a Vertical Channel in the Presence of Electrical Double Layers

Abstract We consider the fully developed mixed convection flow in a vertical channel driven by an external pressure gradient and buoyancy force. Unlike in previous studies, we employ a new model to formulate the flow problem that guarantees the smoothness and continuity of the distributions of the electrical potential and velocity. This model, solved by the homotopy analysis method, is compatible with the channel flow models commonly used in fluid mechanics.

Peristaltic pumping through porous medium in presence of electric double layer

The present paper investigates the peristaltic flow of Newtonian fluids through the porous medium. The effects of electroosmosis mechanism on peristaltic pumping are also considered. An analytical solution is obtained under lubrication approach. Poisson Boltzmann equations are also simplified using Debye linearization. The effects of permeability parameter, electrical double layer thickness and electro-osmotic parameter on the flow characteristics, pressure distribution and shear stress distributions are computed. Numerical computations reveal that electroosmosis and permeability play vital role in peristaltic pumping. The findings of present study may be applicable in biomedical engineering and chemical engineering where peristaltic micropumps may be designed.

Plasma density accumulation on a conical surface for diffusion along a diverging magnetic field

Two-dimensional (2-D) density and potential measurements have been carried out for plasma diffusing through an aperture in a diverging magnetic field. The radial density profile near the source is peaked on the axis but gradually evolves into a hollow profile away from the source. We observe a slow increase of the peak density along a hollow conical surface and correlate with the 2-D potential measurement reported earlier. It is also shown that the formation of 2-D structures with similar features are observed whenever plasma is allowed to diffuse through a physical aperture in such diverging magnetic field configuration, with or without the presence of electric double layer, i.e., the phenomenon is generic in nature.

Study of Electroosmotic Flow in a Nanotube with Power Law Fluid

In this paper, electroosmotic phenomena in power law fluids are investigated. This assumption is applicable in many cases such as blood. Flow channels assumed to be in nanoscale. Navier-Stokes, Poisson-Boltzmann and electrochemical equilibrium equations govern these phenomena. It is notable that, these governing equations should be modified according to fluid complexity. Electroosmotic phenomena occur in the presence of electric double layer (EDL). Potential in the edge of the inner layer (stern layer) is called zeta potential. In this paper, according to follow the applicability of the subject, zeta potential is assumed to be so small, that makes the Poisson-Boltzmann equation linear and be able to solve analytically. Method employed for analytical solution is based on developed Bessel differential equation. This paper aims to investigate the fluid properties, zeta potential and Debye-Huckel parameter effect on the viscosity, electroosmotic mobility and velocity field in the nanotube. These expected achievements help us to study the properties of blood and some other non-Newtonian fluids more precisely.

Limitations of Equivalent Circuit Models in Data-Driven Simulation of the Neuron-Electrode Interface

Noninvasive neuroelectronic interfacing has important applications in the fields of neural prosthetics, biological computation and biosensors. Traditionally, neuron-electrode interfaces have been modeled as linear point or area contact equivalent circuits but such models have not been able to explain the shapes and magnitudes of the experimentally recorded extracellular signals. Also, previous work with Volterra-Wiener characterization of the planar neuron-microelectrode junction using bandlimited Gaussian white noise had shown that the mechanism of signal transduction across the nanoscale neuron-microelectrode cleft region might be nonlinear. In this optimization based study we compared and contrasted experimental and simulation data for point contact models of the extracellular ‘on-cell’ neuron-patch electrode and the planar neuron-microelectrode interface. The nonlinear contributions of the neurons to the dynamics of the equivalent circuit representation of the interfacial medium were systematically isolated by an independent estimation of the ion-channel parameters through a fitting of the simulated intracellular signals to the experimentally recorded voltage and current clamp signals. These ion-channel parameters were then employed in the optimization of the cell-electrode interface parameters based on extracellular recordings obtained from a neuron simultaneously interfaced to the ‘on-cell’ patch-electrode and the planar microelectrode using sub- and supra-threshold stimuli. An examination of the optimized model parameters for the experimental extracellular recordings from sub- and supra-threshold stimulations of the neuron-electrode junctions allowed us to draw important distinctions between the ‘on-cell’ neuron-patch electrode and neuron-microelectrode interfaces that could be attributed to the presence of electric double layer (EDL) and ionic electrodiffusion effects. Based on these results, we then discuss and point out the limitations of the equivalent circuit models in their failure to take account of the nonlinear EDL and ionic electrodiffusion effects occurring during the process of signal transduction at the neuron-electrode interface.

Study of Nanoscale Pressure-Driven Electrokinetic Flow with Effects of Wall Lattice Plane

ABSTRACTThe objective of the present study is to explore pressure-driven flows with the presence of electric double layer (EDL) in nanochannels of various wall lattice planes. Three face-centered cubic (fcc) lattice planes, i.e. fcc(111), fcc(100), and fcc(110), of the channel wall are considered. The structure of diffuse EDL and electrokinetic flow characteristics are dealt with in an atomistic view. Fluid and charge density layering phenomena and their influences on the Stern layer are investigated with the molecular dynamic simulation results. In most of the simulations, a monatomic molecule, W, is used as the solvent model and the charged particles W+ and W− of the same size as the ions. To examine behaviors of the dissimilar particles, a simulation with the aqueous model W for fluid, Na+ for cation and Cl− for anion is also performed. Effects of ion concentrations, wall-fluid interaction energy, and surface charge density on the electro-hydrodynamics are studied. In addition, based on the continuum theory, two analytic expressions for zeta potential with the presence of fluid slippage are derived and analyzed. The present results disclose interesting physics about the influences of wall lattice-fluid interactions, which are significant in further understanding and applications of the nanoscale electrokinetic flows.

Evaluation of corrosion response of sintered ferritic stainless steels using potentiodynamic polarization and electrochemical impedance spectroscopy techniques

The present study investigates the effect of sintering temperature on the electrochemical response of ferritic (434L) stainless steels determined through potentiodynamic polarization and Electrochemical Impedance Spectroscopy (EIS) studies. To understand the corrosion mechanism, the EIS was done at open circuit potential (OCP), passive region (500mV) and near breakdown potential region of polarization curve of 434L stainless steel. The compacts sintered at higher temperature (1400°C) exhibit better corrosion resistance. To explain the EIS results, an electrical circuit has been conceptualized at open circuit potential (OCP) that indicates the presence of two time constants. This can be attributed to the presence of Electrical Double Layer (EDL) and formation of a protective passive during corrosion. EIS results on compacts done at 500mV shows only one time constant which suggests nearly complete passivation of the surface due to the formation of passive film.

Electrically-excited (electroosmotic) flows in microchannels for mixing applications

We propose an asymptotic model for quite general liquid microchannel flows in the presence of electrical double layers (EDLs). The model provides an “inner” solution for the wall layer, which reflects the dominant balance between electrical forces and viscous forces (tangentially), respectively between electrical forces and pressure and viscous forces (normally). The electrically-neutral core of the flow is governed by the standard Navier–Stokes equations, providing the “outer” solution. The asymptotic matching of both solutions provides a method for the simplified numerical treatment of such EDLs. The superposition of the solutions in both regions then allows to infer an approximate solution, valid within the entire domain. Based on this model, we apply external oscillatory electrical fields to excite secondary flows (i) in microchannels with an internal obstacle or (ii) in folded (meander) microchannels. These secondary flows are demonstrated to greatly enhance the mixing of two liquids flowing in a layered fashion through these microchannels. Thus, electrical excitation has considerable potential if micromixers for ionic liquids are designed within electrically-insulating (e.g. plastics, glass) substrates.

The electric double layer effect on the microchannel flow stability and heat transfer

The effect of the electric double layer (EDL) on the linear stability of Poiseuille planar channel flow is reported. It is shown that the EDL destabilises the linear modes, and that the critical Reynolds number decreases significantly when the thickness of the double layer becomes comparable with the height of the channel. First results coming from direct numerical simulations on the non-linear effects show also that the by-pass transition is much more rapid in the presence of EDL. There is an acceptable qualitative correspondence between the estimated transitional Reynolds numbers and some experiments, showing that early transition is plausible in microchannels under some conditions. Several questions remain however unanswered such as the surface conduction effect on EDL.

On the role of ion size in coagulation

It is a well-established fact that the coagulation of colloidal particles suspended in an aqueous medium is affected by the size of the dissolved ions. In general the larger the ions, the more salt is needed to coagulate a suspension. The explanation most commonly given is that the finite size of ions somehow increases the double layer thickness, resulting in a larger critical coagulation concentration (CCC), or more convincingly that the ions adsorb onto colloidal particles and affect the ζ-potential. Without invoking these effects it can be proven that the CCC will increase with ion size because the diffusion and friction coefficients of charged particles are affected by the presence of electrical double layers around them. The reduction in the diffusion coefficient and the increase in the friction coefficient depends explicitly on the size of the ions in the double layer. Provided the ζ-potential is not affected by the size of the ion it is predicted that the CCC increases linearly with the scaled friction coefficient of the ions, in agreement with literature data.