Thickness Of Electric Double Layer Research Articles

Wettability regulation of the electric double-layer structural evolution of complex fluids: Insights into thermodynamic and electrical properties

Understanding the structural evolution at the electrode is essential for accurate prediction of complex fluid applications, where the carbon nanotube is chosen as the carrier of CO2-ionic liquids (ILs) in electroreduction. Then, the electrical double layer with tunable wettability is investigated by molecular dynamics simulations. The competition and cooperation between van der Waals and Coulomb interactions are evaluated by examining the structural and electric characteristics. When an external potential (φ) is initiated, the co-ions are repelled from the electrode and the counter-ions compete with CO2 in the electric double layer (EDL), with different thermodynamics produced by varying the proportion of CO2/ionic liquid. As the solid–liquid interaction parameter (β) increases, more counter-ions aggregate, producing double density peaks for Tf2N− and sharply increasing the density of CO2. With increases in β and φ, the local charge density and local field potential increase, and the EDL thickness decreases. However, the location of the CO2 density layer shifts ahead to the counter-ions, weakening their shielding effect and capacitance. Using a combination of structural analysis, the first and second peaks of Tf2N− of EDL are composed of sulfonyl and trifluoromethyl, respectively. As a response, the steric hindrance of CO2 decreases, and more molecules migrate to the surface in a parallel orientation. The structural evolution is quantitatively evaluated in terms of the entropy, results show that the orientation transition is prominent in structural evolution. The coupling relation between thermodynamic and electrical properties plays a pivotal role in determining the structural evolution of complex mixtures, and these findings could benefit the advancement of ILs-based CO2 electroreduction and other complex fluid applications.

Ion Transport Through Nanopores and the Effects of Pore Wall-Ion Interaction.

Ion transport inside nanopores is affected by the physicochemical interactions between the ions and the internal pore wall, offering novel opportunities useful for nanopore-based applications. Here we demonstrate that the transport of Fe(CN)63-/4- is influenced by the pore wall-ion interactions in sub-10 nm pore channels of a mesoporous zirconia film (MZF) formed on an electrode based on cyclic voltammetric (CV) studies. At pH lower than the point of zero charge of zirconia, the pore wall is positively charged, enabling it to exert attractive interaction with the negatively charged analyte ions. Moreover, experimental data indicate that the attractive interaction strongly favors the more highly charged Fe(CN)64- ions over the Fe(CN)63- ions. These effects affect the ion transport through the MZF nanopore channels, which is manifested by a number of different sets of data, including the positive shift of the reduction potential, the disparity between the CV curves of the anodic and cathodic sweeps, and the splitting of the single pair of redox peaks into two pairs when the electrical double layer thickness is increased by reducing the concentration of the supporting electrolyte. Each of these observations can be explained by the wall-ion interactions. Our findings may lead to further explorations into the transport of redox ions that interact differently with the pores and into the development of novel applications based on nanopores.

Applied Electric Field Effects on Diffusivity and Electrical Double-Layer Thickness.

This study utilizes molecular dynamics (MD) simulations and continuum frameworks to explore electroosmotic flow (EOF) in nanoconfined aqueous electrolytes, offering a promising alternative to conventional micro-/nanofluidic systems. Although osmotic behavior in these environments is deeply linked to local fluid properties and interfacial dynamics between the fluid and electrolyte solutions, achieving a complete molecular-level understanding has remained challenging. The findings establish a linear relationship between electric field strength and fluid velocity, uncovering two distinct transport regimes separated by a critical threshold, with a markedly intensified flow in the second regime. It is demonstrated that rising electric field strengths significantly enhance water diffusion coefficients, supported by a detailed analysis of fluid hydration structures, the potential of mean force (PMF), and local stress tensors. Due to the applied electric field strength, the motion of ions and water accelerates, leading to the redistribution of ions and intensification of electrostatic forces. This expands the thickness of the electric double layer (EDL) and amplifies fluid diffusivity, thereby enhancing nanoscale fluid activity. These insights enhance the molecular-level understanding of EOF and define the stability of flow regimes, providing valuable guidelines for advancing nanofluidic technologies, such as drug delivery systems and lab-on-a-chip devices.

Voltage-induced modulation of interfacial ionic liquids measured using surface plasmon resonant grating nanostructures.

We have used surface plasmon resonant metal gratings to induce and probe the dielectric response (i.e., electro-optic modulation) of ionic liquids (ILs) at electrode interfaces. Here, the cross-plane electric field at the electrode surface modulates the refractive index of the IL due to the Pockels effect. This is observed as a shift in the resonant angle of the grating (i.e., Δϕ), which can be related to the change in the local index of refraction of the electrolyte (i.e., Δnlocal). The reflection modulation of the IL is compared against a polar (D2O) and a non-polar solvent (benzene) to confirm the electro-optic origin of resonance shift. The electrostatic accumulation of ions from the IL induces local index changes to the gratings over the extent of electrical double layer (EDL) thickness. Finite difference time domain simulations are used to relate the observed shifts in the plasmon resonance and change in reflection to the change in the local index of refraction of the electrolyte and the thickness of the EDL. Simultaneously using the wavelength and intensity shift of the resonance enables us to determine both the effective thickness and Δn of the double layer. We believe that this technique can be used more broadly, allowing the dynamics associated with the potential-induced ordering and rearrangement of ionic species in electrode-solution interfaces.

Unsteady solute dispersion of electro-osmotic flow of micropolar fluid in a rectangular microchannel

This study scrutinizes the two-dimensional concentration distribution for a solute cloud containing a micropolar fluid in a rectangular microchannel under the influence of an applied electric field. The concentration distribution is obtained up to second order approximation using Mei's homogenization method. Analytical formulas are derived for dispersion coefficient, mean and two-dimensional concentration distributions. This study also includes the analytical expressions for electric potential, velocity, and microrotation profiles. This study discusses the impact of coupling number, couple stress parameter, electric double layer thickness, and Péclet number on solute concentration distribution. The results of fluid velocity and dispersion coefficient are validated with available works in the literature. The non-Newtonian parameter and electric double layer thickness are shown to have a significant impact on dispersion. Our study reveals that concentration distribution rises but spreading of solute reduces when the coupling number increases. This is also true when the Debye length decreases. It is also obtained that the solute spreads more in the Newtonian fluid case compared to the micropolar fluid case. Finally, coupling number and electric double layer thickness show a symmetric pattern to the indicator function for the transverse concentration variation rate. The findings of this work have broad implications in deoxyribonucleic acid analysis, chemical mixing, and separation.

Electrolyte‐Tailored Heterostructured Zinc Metal Anodes with Tunable Electric Double Layer for Fast‐Cycling Aqueous Zinc Batteries

AbstractThe structures and properties of the electric double layer (EDL) on zinc (Zn) anodes significantly influence the cycling and rate performance of aqueous Zn batteries (ZBs). Here, a strategy is reported to regulate the EDL structure through work function (Wf) engineering to effectively enhance the electrochemical performance of ZBs, which is enabled by electrolyte‐tailored growth of heterogenous metal with a large Wf on the Zn anode. The metal‐to‐metal charge transfer in heterostructured Zn metal induced by the disparity of Wf increases the surface charge density, which enriches the Zn ions and shortens the thickness of EDL. The compressed EDL weakens the repulsive force of Zn deposits to achieve a tightly stacked and dendrite‐free Zn deposition. Besides, the formed H2O‐deficient EDL structure enables the inorganic‐rich solid electrolyte interphase (SEI) with high Zn‐ion conductivity to inhibit the notorious parasitic reactions and improve the electrode reaction kinetics. Consequently, the Zn||Zn symmetric cells demonstrate an ultra‐long cycling life over 2700 cycles (the cumulative capacity reaches 5400 mA h cm−2) at a high current density of 50 mA cm−2. The Zn anodes show a high average Coulombic efficiency of 99.70% over 3650 cycles. The Zn||MnO2 full cells exhibit excellent practical‐level performance under cyclic continuous mode (3000‐cycle life at high rates) and cyclic intermittent mode (1170‐cycle life with 83.05% capacity retention). Practical pouch cells are also demonstrated with outstanding cycling performance.

Exploring the mechanical behavior and microstructure of compacted loess subjected to dry-wet cycles and chemical contamination

Due to climatic factors and rapid urbanization, the soil in the Loess Plateau， China, experiences the coupled effects of dry-wet cycles and chemical contamination. Understanding the mechanical behavior and corresponding microstructural evolution of contaminated loess subjected to dry-wet cycles is essential to elucidate the soil degradation mechanism. Therefore, direct shear and consolidation tests were performed to investigate the variations in mechanical properties of compacted loess contaminated with acetic acid, sodium hydroxide, and sodium sulfate during dry-wet cycles. The mechanical response mechanisms were investigated using zeta potential, mineral chemical composition, and scanning electron microscopy (SEM) tests. The results indicate that the mechanical deterioration of sodium hydroxide-contaminated loess during dry-wet cycles decreases with increasing contaminant concentration, which is mainly attributed to the thickening of the electrical double layer (EDL) by Na+ and the precipitation of calcite, as well as the formation of colloidal flocs induced by OH−, thus inhibiting the development of large pores during the dry-wet process. In contrast, the attenuation of mechanical properties of both acetic acid- and sodium sulfate-contaminated loess becomes more severe with increasing contaminant concentration, with the latter being more particularly significant. This is primarily due to the reduction of the EDL thickness and the erosion of cement in the acidic environment, which facilitates the connectivity of pores during dry-wet cycles. Furthermore, the salt expansion generated by the drying process of saline loess further intensifies the structural disturbance. Consequently, the mechanical performance of compacted loess is sensitive to both pollutant type and concentration, exhibiting different response patterns in the dry-wet cycling condition.

A network model to predict ionic transport in porous materials

Understanding the dynamics of electric-double-layer (EDL) charging in porous media is essential for advancements in next-generation energy storage devices. Due to the high computational demands of direct numerical simulations and a lack of interfacial boundary conditions for reduced-order models, the current understanding of EDL charging is limited to simple geometries. Here, we present a network model to predict EDL charging in arbitrary networks of long pores in the Debye-Hückel limit without restrictions on EDL thickness and pore radii. We demonstrate that electrolyte transport is described by Kirchhoff's laws in terms of the electrochemical potential of charge (the valence-weighted average of the ion electrochemical potentials) instead of the electric potential. By employing the equivalent circuit representation suggested by these modified Kirchhoff's laws, our methodology accurately captures the spatial and temporal dependencies of charge density and electric potential, matching results obtained from computationally intensive direct numerical simulations. Our network model provides results up to six orders of magnitude faster, enabling the efficient simulation of a triangular lattice of five thousand pores in 6 min. We employ the framework to study the impact of pore connectivity and polydispersity on electrode charging dynamics for pore networks and discuss how these factors affect the time scale, energy density, and power density of capacitive charging. The scalability and versatility of our methodology make it a rational tool for designing 3D-printed electrodes and for interpreting geometric effects on electrode impedance spectroscopy measurements.

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.