Thickness Of Electric Double Layer Research Articles

Eliminating lithium dendrites via dependable ion regulation of charged nanochannels

Reviving lithium metal anode is of great significance to developing high-energy-density batteries after addressing the lithium dendrite. Constructing functional separator with charged nanochannel configuration has been proven to be an effective way to inhibit nucleation of lithium dendrites due to the achievement of a fast and selective lithium ion transport. While the ion regulation capability of existing functional separators cannot be maximized because their nanochannels are much larger than the electric double layer (EDL) regions that dominate ion transport. Considering the tiny EDL thickness (∼1 nm) formed in the electrolyte, the sulfonate-rich covalent organic framework (COF) is developed as functional separator to achieve a dependable ion regulation based on the nano-confined channel (∼1.55 nm) and surface negative charges. Consequently, a high Li+ transference number tLi+ (0.85) and sufficient ionic conductivity (0.53 mS cm−1) are obtained simultaneously, which effectively alleviates dendrite nucleation and growth of lithium metal anode for over 1000 h. Moreover, the principle for fast and selective lithium-ion transport is revealed from a new perspective of EDL region embedded in the nanochannel. Overall, this work demonstrates a strategy to eliminate lithium dendrites via ion regulation of charged nanochannels, which is anticipated to promote the practical application of lithium metal batteries.

Evaluating the efficacy of newly synthesized amino acid derivatives as corrosion inhibitors in acidic solutions

Three benzimidazole derivatives, with tryptophan (BIT), tyrosine (BIY), and histidine (BIH) amino acid units, have remarkable protective properties as eco-friendly corrosion inhibitors for steel under severe acidic conditions. At a temperature of 303 K, the corrosion inhibition efficiency of BIT, BIY, and BIH at a concentration of 10 mM is 90.09 %, 92.53 %, and 93.43 %, respectively. Electrochemical tests indicate that the adsorption of these substances on the substrate leads to an increase in charge transfer resistance and interfacial electric double layer thickness. This effectively hinders the dissolution of metal and the evolution of hydrogen. The analysis of the surface structure and appearance using SEM-EDS indicates that the inhibitors have the ability to create a protective coating through both chemical and physical bonding, effectively protecting the metal from corrosive substances. Theoretical calculations, such as Density Functional Theory (DFT) and Natural Bond Orbital (NBO) analysis, along with FUKUI analysis, help identify active sites and adsorption configuration. This enhances our understanding of the corrosion mitigation mechanism. These findings align with the experimental conclusion that the formation of a stable protective film contributes to superior inhibition performance against acidic corrosion conditions.

Interlayer and surface characteristics of carboxymethyl cellulose and tetramethylammonium modified bentonite

This study aims to evaluate interlayer and surface characteristics of carboxymethylcellulose (CMC) and tetramethylammonium (TMA) modified bentonite, named as TCMB, as a potential material in contamination containment systems. The study employed a variety of experimental methods, including zeta-potential, scanning electron microscopy, X-ray diffraction (XRD), transmission electron microscopy, and Fourier transform infrared spectroscopy (FTIR), along with molecular dynamics (MD) simulations. Zeta potential results revealed increased electronegativity in TCMB compared to the conventional bentonite. By forming three-dimensional hydrogel networks capable of filling inter clusters pore spaces, CMC effectively maintained the low hydraulic conductivity of TCMB. XRD results confirmed the presence of TMA in the interlayer of montmorillonite. MD simulations and FTIR analyses validated the successful adsorption of CMC and TMA, which can be jointly attributed to hydrogen bonds between hydroxyl groups in CMC and the surface oxygen of montmorillonite, and electrostatic attraction between TMA and montmorillonite. The comparatively weak bonding between CMC and montmorillonite may facilitate CMC elution in the TCMB exposed to aggressive permeants. Furthermore, the electrical double layer thickness of TCMB and CB was estimated as 31.54 Å and 18.76 Å, respectively. Overall, the CMC and TMA treatments effectively enhance the suitability of bentonite for contamination containment applications.

Understanding electrostatic interaction on strong cation-exchanger via co-ion valency effects

Empirical adsorption models have been extensively used to design and optimize ion exchange chromatography (IEC) processes for proteins. The equations go 40 years back to the qualitative findings about the electrical double layer (EDL) in ion exchangers and form the basis of the stoichiometric displacement (SD) model widely used in preparative chromatography. While the SD model reduces the experimental effort to find salt-eluting conditions for the separation, knowledge transfer is restricted from one system to another. However, this limitation can be overcome by understanding the physicochemical interaction mechanism between the solid adsorbent and the electrolyte. Via a theoretical and experimental approach, we investigated the physicochemical adsorption mechanism in IEC and developed a methodology to determine it quantitatively by measuring the effective EDL thickness. We performed negative adsorption experiments in high-performance liquid chromatography to measure the excluded volume of co-ions, citrate, or oxalate on strong cation exchange resin. Together with the physical specifications of the column and the deployment of a modified nonlinear Poisson-Boltzmann equation, we identified the effects of the electrolyte composition on the size of the EDL. While it depends on the concentration, valency, and size of the counterion, we derived that the expansion of the EDL is indicated by different valencies of the carboxylate co-ions in trace amounts. Our findings provide a self-consistent theory of the transport phenomena in a solid/fluid system with all parameters specified with the physical properties of the chromatographic process. Further, optimizing the resin design or improving the adsorption and desorption conditions for biomolecules may be facilitated. Altogether, our work may improve material designing and process development and, thereby, help to overcome the concurrent technological and economic bottlenecks of the well-deployed purification step of IEC.

Regulating Chemisorption and Electrosorption Activity for Efficient Uptake of Rare Earth Elements in Low Concentration on Oxygen-Doped Molybdenum Disulfide.

Recovery of rare earth elements (REEs) with trace amount in environmental applications and nuclear energy is becoming an increasingly urgent issue due to their genotoxicity and important role in society. Here, highly efficient recovery of low-concentration REEs from aqueous solutions by an enhanced chemisorption and electrosorption process of oxygen-doped molybdenum disulfide (O-doped MoS2) electrodes is performed. All REEs could be extremely recovered through a chemisorption and electrosorption coupling (CEC) method, and sorption behaviors were related with their outer-shell electrons. Light, medium, and heavy ((La(III), Gd(III), and Y(III)) rare earth elements were chosen for further investigating the adsorption and recovery performances under low-concentration conditions. Recovery of REEs could approach 100% under a low initial concentration condition where different recovery behaviors occurred with variable chemisorption interactions between REEs and O-doped MoS2. Experimental and theoretical results proved that doping O in MoS2 not only reduced the transfer resistance and improved the electrical double layer thickness of ion storage but also enhanced the chemical interaction of REEs and MoS2. Various outer-shell electrons of REEs performed different surficial chemisorption interactions with exposed sulfur and oxygen atoms of O-doped MoS2. Effects of variants including environmental conditions and operating parameters, such as applied voltage, initial concentration, pH condition, and electrode distance on adsorption capacity and recovery of REEs were examined to optimize the recovery process in order to achieve an ideal selective recovery of REEs. The total desorption of REEs from the O-doped MoS2 electrode was realized within 120 min while the electrode demonstrated a good cycling performance. This work presented a prospective way in establishing a CEC process with a two-dimensional metal sulfide electrode through structure engineering for efficient recovery of REEs within a low concentration range.

Fines migration characteristics of illite in clayey silt sediments induced by pore water under the depressurization of natural gas hydrate

Marine gas hydrate is widely distributed in clayey silt sediments, which have high clay content and low permeability. The decomposition of natural gas hydrate will cause the mechanical failure of the reservoir and the decrease of pore water salinity, inducing the migration of clay minerals to clog the pore throat, which has a significant impact on the production efficiency of natural gas hydrate. In this work, the migration behaviour of illite in clayey silt sediments driven by pore water under the depressurization of hydrate was studied through pressure difference, pore throat and content changes. We studied the migration process of silt, excluding the interference of synergistic migration of silt and illite, and then studied the migration of illite under the change of flow rate and salinity. The results show that illite will migrate before silt and that critical flow rate and critical salinity exist. The flow rate mainly affects the torque generated by the forces detaching the illite particles. Illite particle detachment will occur if the flow rate exceeds the critical value and the torque balance is disrupted, and then the pore throat is clogged. There are two effects of salinity decrease on illite migration. Above the critical salinity, the expansion of the pore throat due to decomposition has a significant effect on illite migration. Below the critical salinity, the increase of the diffuse electric double layer thickness and the electrostatic repulsion will lead to an increase of the particle concentration in the pore water, making clogging more likely to occur even at low flow rates. This work suggests that clay migration has a complex impact on the development of clayey silt hydrate, and helps to consider the reasonable combination of saturation and production rate when designing a development plan to reduce the impact of permeability decline due to continuous pore throat clogging on development efficiency.

Alteration in electroosmotic flow of couple stress fluids through membrane based microchannel

The fundamentals of electroosmosis are the most fascinating mechanism to induce flow of ionic solution under the effect of external electric field. The electroosmotic flow of the couple stress fluid in a microchannel with an active membrane pumping is analysed in the present model. The upper wall experiences membrane kinematics, generates the pressure to drive the fluid in the microchannel. Governing equations are formulated based on the mass and momentum conservation, and electric potential distribution of ions in diffuse layer. The suitable boundary conditions for the model have been considered. An analytical approach is employed to derive the solutions under the lubrication approximation, and the Debye–Hückel approximation. The effects of electric double layer thickness, couple stress parameter, and Helmholtz-Smoluchowski velocity on the velocity profile, pressure difference, net flow rate, induced streamline velocity, and local wall shear stress are computed for discussion of the physical significance of the model and its applications. Results reveal that electroosmosis mechanisms (axial electric field and electric double layer thickness) has remarkable role in modulating the fluids (Newtonian and non-Newtonian) flow driven by the rhythmic propulsion of membranes in microchannel. It is also worth mentioning that non-Newtonian fluids (couple stress fluids) need more external forces (electric force) to be pumped as compared to Newtonian fluids. Furthermore, it can be analysed that thinner electric double layers (EDLs) elevate wall shear stress, whereas stronger electric fields result in decreased wall shear stress. The results of the model help in designing smart membrane based electric pump for the use in various microscale transport phenomena of bio microfluidics systems.

Unveiling Enhanced Electrostatic Repulsion in Silica Nanosphere Assembly: Formation Dynamics of Body-Centered-Cubic Colloidal Crystals.

We demonstrate the effective establishment of long-range electrostatic interactions among colloidal silica nanospheres through acid treatment, enabling their assembly into colloidal crystals at remarkably low concentrations. This novel method overcomes the conventional limitation in colloidal silica assembly by removing entrapped NH4+ ions and enhancing the electrical double layer (EDL) thickness, offering a time-efficient alternative to increase electrostatic interactions compared with methods like dialysis. The increased EDL thickness facilitates the assembly of SiO2 nanospheres into a body-centered-cubic lattice structure at low particle concentrations, allowing for broad spectrum tunability and high tolerance to particle size polydispersity. Further, we uncover a disorder-order transition during colloidal crystallization at low particle concentrations, with the optimal concentration for crystal formation governed by both thermodynamic and kinetic factors. This work not only provides insights into assembly mechanisms but also paves the way for the design and functionalization of colloidal silica-based photonic crystals in diverse applications.

Benzothiazole-based ionic liquids as environment-friendly and high-efficiency corrosion inhibitors for mild steel in HCl: Experimental and theoretical studies

Two benzothiazole ionic liquids – (E)-3-ethyl-2-(4-hydroxystyryl) benzo[d]thiazol-3-ium iodide ([EHSBT]I) and (E)-3-ethyl-2-(4-hydroxystyryl)benzo[d]thiazol-3-ium bromide ([EHSBT]Br) generate the outstanding protection when employed as green corrosion inhibitors for the steel against aggressive acid solution at different temperatures. The corrosion efficiency of [EHSBT]I and [EHSBT]Br with the low dosage of 0.2 mM is 98.16 % and 89.68 %, respectively, at 303 K. The corrosion inhibition efficiency of [EHSBT]I decreases with the increased temperature and [EHSBT]Br is the opposite. Fortunately, both [EHSBT]I and [EHSBT]Br exhibit the inhibition efficiency of greater than 95 % even when it achieves 333 K, which is ascribed to the dominant chemical adsorption. Likewise, the electrochemical investigation presents the increasement of the charge transfer resistance and interfacial electric double layer thickness due to their adsorption on the substrate, restraining the metal dissolution and hydrogen evolution. The findings of the surface structure and appearance using UV–vis, FT-IR, XPS, SEM-EDS, AFM suggest that the inhibitors can form the complex film ([EHSTB]I-Fe, [EHSTB]Br-Fe) to shield the metal from corrosive particulates via chemical bonding. The confirmation of the active sites and adsorption configuration through theoretical calculation such as DFT and MD, along with RDF, promotes a further comprehension of the corrosion mitigation mechanism, which coincides with the experimental conclusion that the preparation of a stable protective film realizes the superior inhibition performance against high temperature acid corrosion.

The Synergetic Ionic and Electronic Features of MAPbI3 Perovskite Films Revealed by Electrochemical Impedance Spectroscopy

AbstractPerovskites have emerged as a forerunner of electronics research due to their vast potential for optoelectronic applications. The numerous combinations of constituent ions and the potential for doping of perovskites lead to a high demand to track the underlying electronic properties. Solution‐based electrochemistry is particularly promising for detailed and facile assessment of perovskites. Here, electrochemical impedance spectroscopy (EIS) of methylammonium lead iodide (MAPbI3) thin films is performed and model them with an equivalent circuit that accounts for solvent, ionic, and thin film effects. A dielectric constant consistent with prior AC studies and a diffusion constant harmonious with cation motion in MAPbI3 are extracted. An electrical double layer thickness in the perovskite film of 54 nm is obtained, consistent with lithium doping in perovskite films. Comparing the EIS and equivalent circuit model of perovskite films to control ITO‐only data enabled the assignment of the ions at each interface. This comparison implied a double layer of primarily lithium ions inside the perovskite film at the solution interface with significant recombination of ions on the solution side of the interface. This demonstrates EIS as a powerful tool for studying the fundamental charge accumulation and transport processes in perovskite thin films.

Physical–mechanical properties and microstructure degradation of acid–alkali contaminated granite residual soil

Acid—alkali pollution can lead to problems related to surrounding conditions, the health of the earth, and changes in soil physical–mechanical properties and microstructure. However, the response characteristics of acid–alkali pollutants to soil physical–mechanical properties and micro mechanisms under flowing conditions are still unclear. To address this gap, we used a self-developed circulating seepage device to investigate the water–soil chemical interaction of granite residual soil (GRS) under flowing conditions with different pH levels (3, 5, 7, 9, 11, 13) and soaking times (7, 14, 21, 28 days). The results indicate that changes in mineralogy, chemistry, and microstructure are responsible for the changes in physical–mechanical properties of GRS under acid–alkali pollution. We observed that the limit moisture content, shear strength, and internal friction angle of GRS had obvious stages before and after soaking for 7 days. Zeta potential test revealed that EDL in soil has timeliness, which corresponds to physical–mechanical properties. It can be seen that the water–soil chemical interaction of GRS polluted by acid–alkali solutions mainly include the erosion effect and electric double layer (EDL) effect. We found that the thickness of EDL can be characterized by the change in the plasticity index. The plasticity index of GRS under acid erosion is positively correlated with the internal friction angle (IFA), which deviates from the general soil law.

Thermal conductivity effect on thermophoresis of charged spheroidal colloids in aqueous media.

Thermophoresis of spheroidal colloids in aqueous media under the thermal conductivity effect is analyzed. The thermophoretic velocity and the thermodiffusion coefficient of spheroidal colloids have been formulated for extremely thin electric double layer (EDL) cases. Furthermore, a numerical thermophoretic model is built for arbitrary EDL thickness cases. The parametric studies show that the thermal conductivity mismatch of particle and liquid gives rise to a nonlinear temperature region around the spheroid, with the thickness close to the minor semiaxis. When the EDL region is thin relative to such nonlinear temperature region, the thermal conductivity effect on the thermophoresis of spheroidal colloids is significant, which strongly depends on the ratio of the minor semiaxis to the EDL thickness, the thermal conductivity ratio of particle to liquid, and the particle aspect ratio. Finally, to estimate the thermodiffusion coefficient of spheroidal colloids with arbitrary thermal conductivity, electrolyte concentration, and particle shape, the average dimensionless axial temperature gradient on the spheroidal equator plane in the EDL region is proposed.

Dynamic patterns of electroosmosis peristaltic flow of a Bingham fluid model in a complex wavy microchannel

The purpose of this paper is to present a rigorous analysis of streamline patterns and their bifurcation to a viscoplastic Bingham fluid model that involves heat and mass transfer in an electroosmotic flow through a complex wavy microchannel. The Bingham fluid act as a solid medium in the core layer, which divides the channel into three distinct sections utilized to model the problem as a switched dynamical system between these zones. To track multiple steady states (stagnation points) and related trapping phenomena, we perform both analytical and numerical bifurcation analysis of each subsystem with respect to different physical effects such as electrical double layer thickness and Helmholtz-Smoluchowski velocity. The key feature of the technique presented here is its ability to reveal the peristaltic transport characteristics of the Bingham fluid model in the presence or absence of symmetric flow properties. The primary novelty here is the ability to regulate the location and stability of the equilibrium points in the domain of interest. This leads to the detection of global bifurcations that reflect important dynamic elements of the model. Our results highlighted a new category of complex behavior that controls transitions between qualitatively different transport mechanisms, as well as a class of non-classical trapping phenomena.

Ultrasmall Fe2O3 Tubular Nanomotors: The First Example of Swarming Photocatalytic Nanomotors Operating in High-Electrolyte Media.

Self-propelled chemical micro/nanomotors (MNMs) have demonstrated considerable potential in targeted drug delivery, (bio)sensing, and environmental remediation due to their autonomous nature and possible intelligent self-targeting behaviors (e.g., chemotaxis and phototaxis). However, these MNMs are commonly limited by their primary propulsion mechanisms of self-electrophoresis and electrolyte self-diffusiophoresis, making them prone to quenching in high electrolyte environments. Thus, the swarming behaviors of chemical MNMs in high-electrolyte media remain underexplored, despite their potential to enable the execution of complex tasks in high-electrolyte biological media or natural waters. In this study, we develop ultrasmall tubular nanomotors that exhibit ion-tolerant propulsions and collective behaviors. Upon vertical upward UV irradiation, the ultrasmall Fe2O3 tubular nanomotors (Fe2O3 TNMs) demonstrate positive superdiffusive photogravitaxis and can further self-organize into nanoclusters near the substrate in a reversible manner. After self-organization, the Fe2O3 TNMs exhibit a pronounced emergent behavior, allowing them to switch from random superdiffusions to ballistic motions near the substrate. Even at a high electrolyte concentration (Ce), the ultrasmall Fe2O3 TNMs retain a relatively thick electrical double layer (EDL) compared to their size, and the electroosmotic slip flow in their EDL is strong enough to propel them and induce phoretic interactions among them. As a result, the nanomotors can rapidly concentrate near the substrate and then gather into motile nanoclusters in high-electrolyte environments. This work opens a gate for designing swarming ion-tolerant chemical nanomotors and may expedite their applications in biomedicine and environmental remediation.

Mg2+ and Cu2+ Charging Agents Improving Electrophoretic Deposition Efficiency and Coating Adhesion of Nano-TbF3 on Sintered Nd-Fe-B Magnets

In order to prepare nano-TbF3 coating with high quality on the surface of Nd-Fe-B magnets by electrophoretic deposition (EPD) more efficiently, Mg2+ and Cu2+ charging agents are introduced into the electrophoretic suspension and the influence on the electrophoretic deposition is systematically investigated. The results show that the addition of Mg2+ and Cu2+ charging agents can improve the electrophoretic deposition efficiency and coating adhesion of nano-TbF3 powders on sintered Nd-Fe-B magnets. The EPD efficiency increases by 116% with a relative content of Mg2+ as 3%, while it increases by 109% with a relative content of Cu2+ as 5%. Combining the Hamaker equation and diffusion electric double layer theory, the addition of Mg2+ and Cu2+ can change the zeta potential of charged particles, resulting in the improvement of EPD efficiency. The relative content of Mg2+ below 3% and Cu2+ below 5% can increase the thickness of the diffusion electric double layer, the excessive addition of a charging agent will compress the diffusion electric double layer, and thicker diffusion layer represents higher zeta potential. Furthermore, the addition of Mg2+ and Cu2+ charging agents greatly improves the coating adhesion, and the critical load for the cracking of the coating increases to 146.4 mN and 40.2 mN from 17.9 mN, respectively.

Nanoarchitecture factors of solid electrolyte interphase formation via 3D nano-rheology microscopy and surface force-distance spectroscopy

The solid electrolyte interphase in rechargeable Li-ion batteries, its dynamics and, significantly, its nanoscale structure and composition, hold clues to high-performing and safe energy storage. Unfortunately, knowledge of solid electrolyte interphase formation is limited due to the lack of in situ nano-characterization tools for probing solid-liquid interfaces. Here, we link electrochemical atomic force microscopy, three-dimensional nano-rheology microscopy and surface force-distance spectroscopy, to study, in situ and operando, the dynamic formation of the solid electrolyte interphase starting from a few 0.1 nm thick electrical double layer to the full three-dimensional nanostructured solid electrolyte interphase on the typical graphite basal and edge planes in a Li-ion battery negative electrode. By probing the arrangement of solvent molecules and ions within the electric double layer and quantifying the three-dimensional mechanical property distribution of organic and inorganic components in the as-formed solid electrolyte interphase layer, we reveal the nanoarchitecture factors and atomistic picture of initial solid electrolyte interphase formation on graphite-based negative electrodes in strongly and weakly solvating electrolytes.

Morphological Evolution of Gold Nanoparticles Synthesized via Solution Plasma Sputtering: Effect of Sodium Chloride Concentration and Storage Time

Morphological control of gold nanoparticles (AuNPs) is vital for tuning their optical, chemical, physical, and catalytic properties for desired specific applications. Despite numerous efforts dedicated in recent years, controlling the morphology of AuNPs synthesized via solution plasma sputtering (SPS) remains a challenge, requiring further investigation. Herein, AuNPs were synthesized via SPS in sodium chloride (NaCl) solutions of various concentrations (0.5, 1, 2, and 5 mM). Evolutions of localized surface plasmon resonance and morphology of AuNPs over a 30 day storage period were thoroughly examined using ultraviolet–visible spectroscopy and field-emission transmission electron microscopy. The formation and growth mechanisms of AuNPs during and after synthesis provide more insights into this nascent field. At the initial storage time, AuNPs with chain-like structures were observed at all the NaCl concentrations. Their size tended to increase from 6 to 10 nm with a broader size distribution with increasing NaCl concentration. At a prolonged storage time of 15 days, AuNPs became smaller and more isolated at all NaCl concentrations owing to the oxidative etching effect. After 30 days of storage, the number of Au ions dissolved from etching slowly reduced and grew on the AuNPs, affording increased particle sizes. The interplay between etching and growth processes proceeded until reaching equilibrium. AuNPs exhibited good colloidal stability at low NaCl concentrations (i.e., 0.5, 1, and 2 mM); however, coalescence and sedimentation occurred at a high NaCl concentration of 5 mM owing to a considerable reduction in the electrical double-layer thickness. These results demonstrated that the NaCl concentration and storage time crucially affect the morphological evolution and stability of AuNPs synthesized via SPS.

Quantifying Coupling Effects Between Soil Matric Potential and Osmotic Potential

AbstractSoil matric potential and osmotic potential are widely accepted as two independent components of total soil water potential. However, laboratory observations repeatedly demonstrated that matric potential can vary with salt concentration, implying a potential coupling between matric potential and osmotic potential. To date, it remains elusive whether matric potential and osmotic potential are independent or not and why so, and a theoretical theory for quantifying the coupling between them is still missing. Herein, a theoretical model is developed to quantitatively explain this problem via a lens provided by a recent concept of soil sorptive potential (SSP). The proposed model substantiates that matric potential and osmotic potential are not independent. The increasing salt concentration can notably depress two variables underpinning SSP, namely relative permittivity and electrical double layer thickness, leading to non‐negligible decreasing (more negative) of matric potential in the high suction range, and increasing (less negative) of it in the low suction range. In turn, the soil‐water interactions redistribute ions in soil water, raising osmotic potential especially for clay with high cation exchange capacity. The proposed model shows excellent performance in capturing experimental data, validating its accuracy. A parametric study implies that the neglection of coupling effects can lead to a significant underestimation of soil hydraulic conductivity in the film flow regime.

Transient solute dispersion in electro‐osmotic viscoplastic flow in a microchannel

AbstractThe transport of a neutral solute in incompressible electro‐osmotic flow of Bingham plastic non‐Newtonian liquid flowing through a microchannel is studied theoretically. The flow is driven by a constant axially applied electric field. The non‐dimensional conservation equations with associated boundary conditions are solved with Gill's series expansion technique. The whole transport process is analyzed using three transport coefficients, namely, advection coefficient, dispersion coefficient and the apparent asymmetry coefficient, respectively. The mean concentration distribution of the solute is calculated via a third‐order approximation of the series expansion. The study investigates the collective effects of yield stress and electric double layer (EDL) thickness (inverse Debye length) on the transport of solute. The long‐term behaviour of mean concentration distribution is shown to be accurately predicted by second‐order approximations; however, utilizing third or higher order approximations in Gill's series expansion enables a more refined analysis of the small and moderate time behavior of transport coefficients. The present analysis is relevant to emerging applications in bio‐microfluidics exploiting electroviscous fluent media.

Study of the Seismoelectric Effect in Saturated Porous Media Using a Bundle of Capillary Tubes Model

The seismoelectric effect is the fundamental basis for seismoelectric logging. Most of the existing theories for the seismoelectric effect are based on the Pride theory, which adopts the assumption of a thin electric double layer and uses the volume-averaging method to derive the seismoelectric coupling equations; hence, the obtained electrokinetic coupling coefficient is not applicable to large-Debye-length cases. In addition, the Pride theory neglects the change in seepage velocity with the radial position of the pore when calculating the streaming current, which leads to an inaccurate reflection of the influence of pore size on the electrokinetic coupling coefficient. In this study, we proposed a flux-averaging method to solve the effective net residual charge density of porous media and further derived the electrokinetic coupling coefficient expressed by the effective net residual charge density. We also investigated the effect of formation parameters and compared the results with those calculated using the Pride theory. Since the proposed method is not limited by the thin electric double layer assumption, it is suitable for both small- and large-Debye-length cases. Moreover, we also carried out flume experiments to investigate the influence of salinity, where both thin and thick electric double layer cases were studied. The comparison between the results of the experiment and simulation verified the correctness of the proposed method. Furthermore, the proposed method took into account the variation in seepage velocity with pore location when solving for the streaming current; therefore, the influence of the pore size on the electrokinetic coefficient can be described more accurately.