Electrokinetic Behavior Research Articles

Numerical characterization of inter-core coalescence by AC dielectrophoresis in double-emulsion droplets.

The utilization of an alternating current electric field provides a good means to achieve controlled coalescence between paired inner cores encapsulated in water-in-oil-in-water double-emulsion (DE) droplets. Although previous studies have experimentally determined the conditions under which inter-core electrokinetic fusion occurs, the transient interfacial dielectrophoretic (DEP) dynamics key to understand the underlying fluid mechanics is still unclear from a physical point of view. By coupling DEP motion of two-phase flow to phase-field formulation, bulk-coupled numerical simulations are conducted to characterize the spatial-temporal evolution of the surface charge wave and the resulting nonlinear electrical force induced at both the core/shell and medium/shell oil/water interfaces. The effect of interfacial charge relaxation and droplet geometry on inter-core attractive dipolar interaction is investigated within a wide parametric space, and four distinct device operation modes, including normal inter-core fusion, shell elongation, partial core leakage, and complete core release, are well distinguished from one another by flow regime argumentation. Our results herein reveal for the first time the hitherto unknown transient electrohydrodynamic fluid motion of DE droplet driven by Maxwell-Wagner structural polarization. The dynamic simulation method proposed in present study points out an effective outlet to predict the nonlinear electrokinetic behavior of multicore DE droplets for realizing a more controlled triggering of microscale reactions for a wide range of applications in drug discovery, skin care, and food industry.

Electrokinetic behavior of conical nanopores functionalized with two polyelectrolyte layers: effect of pH gradient.

The behavior of ionic current rectification of a conical nanopore functionalized with two polyelectrolyte (PE) layers via layer-by-layer deposition subject to an extra applied pH gradient is investigated theoretically. The applied pH, the electric potential, the half-cone angle of the conical nanopore, and the fixed charge densities of the PE layers are examined in detail for their influence on the ionic current rectification (ICR) behavior of the nanopore. We found that this behavior depends highly on the direction of the pH gradient, which arises because the associated electroosmotic flow plays a significant role. The mechanisms of ionic transport in the present pH asymmetric system are discussed. The results gathered reveal that the ICR behavior of a nanopore can be tuned effectively by applying an extra pH gradient. We also examine the case where two PE layers are uniformly merged into one layer. In this case, both the fixed charge density and the concentration profile are quite different from those when two PE layers are present.

Evaluating the electrokinetic behavior of the acrylonitrile based Zn(II) ion-imprinted cross-linked polymer adsorbent for the Zn(II) ions selective removal from aqueous medium

Evaluating the electrokinetic behavior of the acrylonitrile based Zn(II) ion-imprinted cross-linked polymer adsorbent for the Zn(II) ions selective removal from aqueous medium

Comprehensive Investigation of Electrokinetic Behavior of Carbonate-Brine Interface for Calcite and Dolomite Particles: Implications for Enhanced Oil Recovery

Comprehensive Investigation of Electrokinetic Behavior of Carbonate-Brine Interface for Calcite and Dolomite Particles: Implications for Enhanced Oil Recovery

Influence of chemical and crystallite parameters of asphaltenes on their thermal decomposition and electrokinetic behavior

This study aims to explore the influence of chemical composition and structural features of asphaltenes from heavy and light crude oils on their thermal degradation, kinetic parameters and electrophoretic mobility. Non-isothermal pyrolysis experiments were performed through thermogravimetric (TG) analysis whereas electrophoretic mobility was evaluated through zeta-potential measurements. Results showed that thermal degradation profile, reaction rate and kinetics of the asphaltenes pyrolysis can be associated to their XRD structural parameters such as aromatic-stack height, aromatic-sheet diameter, and size of peripheral alkyl groups. In addition, the influence of crystallite parameters, salinity, sulfur, and metal content on the asphaltenes electrokinetic behavior, was explored.

Interplay Between Ca2+, Mg2+, and SO42– Ions and Their Influence on the Zeta-Potential of Limestone during Controlled-Salinity Waterflooding

Substantially enhanced oil recoveries from carbonate reservoirs have been accredited to the modification of ionic content and salinity of the injection water and subsequent alteration of reservoir rock wettability toward more water-wet. Modification of surface charges at rock/oil/water interfaces is believed to be the main mechanism that controls the process of wettability alteration. This paper presents a systematic zeta-potential measurement study that investigates the individual and relative impacts of Ca2+, Mg2+, and SO42– ions on a limestone rock from the Middle East. The main target of the study is to understand the impact of each potential determining ion individually and in the presence of another ion for insightful explanations of the overall impact of injection water during ionically controlled waterflooding in carbonate reservoirs. The novelty of the current study is the comprehensive investigation of the interplay between potential determining ions and the resultant impact on limestone surface charges. Different modified brines were prepared based on the ionic composition of Arabian Gulf seawater, which is the main source of injection water in the region. Model oil, containing carboxylic acid, was used to represent the oil phase in aging procedures. Interactions at the rock/oil/water interfaces were assessed using zeta-potential measurements of unaged and aged limestone particles. The results show that Ca2+, Mg2+, and SO42– are potential determining ions that can alter surface charges of unaged and aged limestone. SO42– ions were found to have a profound impact on the generation of negative surface charges on limestone as well as in suppressing the preferential ability of Ca2+ and Mg2+ ions to generate positive surface charges. Results also showed that limestone possesses negative surface charges when conditioned in unmodified seawater and twice diluted seawater. Comparing the obtained results from this study with the literature suggests that similarities in the mineralogical composition of carbonates rocks do not necessarily reflect in similar electrokinetic behavior, even under the same experimental conditions. Moreover, this study shows that the zeta-potential of limestone is not linearly correlated with decreased salinity. Furthermore, it is shown that conditioning limestone in sequentially diluted seawater will result in an increase in the magnitude of the negative charges up to twice diluted seawater, after which the magnitude of the negative surface charges will start to decrease. This finding suggests that a different mechanism is responsible for the modification of carbonate surface charges during late stages of sequential low-salinity waterflooding than the mechanism that controls the modification of surface charges during early stages of the process.

Space charge modulation and ion current rectification of a cylindrical nanopore functionalized with polyelectrolyte brushes subject to an applied pH-gradient

Considering versatile potential applications of bioinspired membranes, we simulate the electrokinetic behavior of a cylindrical nanopore, surface modified by a polyelectrolyte (PE) layer. Taking account of the effect of electroosmotic flow and an additionally applied pH gradient, the influences of the strength of the pH gradient, the PE layer thickness, the length of the nanopore and its radius on its conductance and ion current rectification (ICR) performance are assessed. We show that if pHU (the pH at the higher pH end of the nanopore) is fixed at 11 and pHL (the pH at the lower pH end of the nanopore) varies from 3 to 11, the rectification factor Rf has a local maximum occurring in 6 < pHL <8; the greater the magnitude of the applied potential bias |V| the smaller the pHL at which the local maximum occurs. The influence of the PE layer thickness on the nanopore rectification performance is important only if 5 < pHL <8, and the optimum performance is reached at a medium thick PE layer (ca. 3 nm). Possible mechanisms associated with the ion transport phenomenon under consideration are proposed and discussed in detail.

Investigation of the interactions of cationic guar with human hair by electrokinetic analysis.

ObjectiveCationic guar is an important polysaccharide used as a hair conditioning agent in personal care products. In this article, we report streaming potential data demonstrating its behaviour as it interacts electrostatically with hair. Several cationic guar variants with different molecular weights (MWs) and charge densities (CDs) were examined.MethodsAll experiments were carried out with a custom‐designed streaming potential instrument so that in situ, real‐time data were monitored during the treatment of a hair plug with aqueous solutions of cationic guar and subsequent treatment with anionic surfactants—sodium laureth sulfate (SLES) and cocamidopropyl betaine (CAPB)—commonly found in contemporary shampoo formulations.ResultsThe MW of the cationic guar variants plays an integral role in determining the thickness of the adsorbed polymer layer on the hair surface while CD influences the zeta potential. Data were also generated for the treatment of hair with a cationic flexible polymer (polyquaternium‐28) and cationic conditioning surfactant (behentrimonium chloride) to provide a frame of reference. The deposition behaviour on hair of high MW cationic guar variants is distinct from these conventional molecules in terms of its electrokinetic properties. We also examined the electrokinetic behaviour of cationic guar on hair types from different racial backgrounds. While the cationic guar treatment yielded similar results for the different hair types, anionic surfactant treatment resulted in quicker sorption and desorption from African, European 65% grey, and Mulatto hair as compared to Chinese, European dark brown, and Indian hair.ConclusionWe introduce an in situ technique for measuring the dynamic sorption/desorption of charged molecules on the surface of human hair. Evaluation of a series of cationic guar species revealed varying behaviour depending on the MW and CD of the polysaccharide. Our data also demonstrate differences in the desorption properties of typical shampoo surfactants for hair from diverse racial backgrounds.

Influence of choline chloride based natural deep eutectic solvent on the separation and rheological behavior of stable bentonite suspension

• Electrokinetic and rheological behavior of treated bentonite suspension were studied. • NADES showed better performance compared to ChCl-LA mixture. • NADES treated suspensions showed pseudoplastic and time-dependent behavior. • Solid-like behavior ( G ' > G ' ' ) was observed in all treated suspensions. • The destabilization degree and rheological behavior were in good agreement. Colloids in wastewater are considered a serious problem due to their stability and separation difficulty. Coagulation/ flocculation processes are the most common for the separation of colloids because of their high-performance efficiency, simplicity, and economical characteristic. Natural deep eutectic solvents (NADES) are green solvents that proved to be highly effective in the destabilization of colloidal suspensions. In the present study, the influence of choline chloride (ChCl) and lactic acid (LA) based NADES on the rheological behavior of bentonite suspension was investigated. Furthermore, it examines the difference in the rheological behavior of NADES treated suspension with others treated with ChCl-LA mixture (LA and ChCl added one after the other). The rheological behavior are correlated to the destabilization degree of each coagulants through turbidity reduction, zeta potential, particle size distribution, and capillary suction time. The study revealed that while untreated bentonite suspension follows a Newtonian behavior, treated suspensions are non-Newtonian fluids with shear thinning behavior. Furthermore, all treated suspensions showed elastic behavior under moderate to low oscillatory frequencies. The changes in the studied rheological parameters (i.e., initial viscosity, elastic modulus, and Bingham yield stress) were influenced by the concentration in addition to the structure of the selected coagulant. The addition of higher coagulant concentration enhances the elastic properties from two to more than ten times depending on the concentration and coagulant type. At concentration of 6.76 × 10 - 2 M , suspension treated with NADES achieved an initial viscosity of 194 , 110 m P a . s and a yield stress of 2959.3 m P a which indicates the formation of stronger and stiffer flocs. On the other hand, ChCl-LA treated suspension had viscosity and yield stress of 9 and 15 magnitudes lower, respectively. Enhancing the rheological behavior of suspensions is usually attributed to higher destabilization degree, which is desirable for the further treatment processes. By increasing the concentration from 5.9 × 10 - 3 M to 6.76 × 10 - 2 M , turbidity reduction increases from 12 % to 99.9 % with an increase in the floc size from 3.3 μ m to 27.3 μ m for NADES treated suspension. The increase in the destabilization degree was associated with an enhancement in the suspension viscosity by more than two folds.

Electrosteric stabilization of oil/water emulsions by adsorption of chitosan oligosaccharides—An electrokinetic study

The present study was focused on investigation of electrokinetic behaviour of lecithin-stabilized oil/water emulsions in the presence of chitosan oligosaccharides (COS). The oligosaccharides give unique opportunity for precisely characterization of the properties of chitosan as a function of the degree of acetylation (DA) and degree of polymerization (DP) of the polymer. For the study were chosen well characterized ultra pure COS molecules with completely acetylated monomers and mixture of COS molecules with acetylated and deacetylated monomers. The obtained results confirmed experimentally for the first time, the suggestion for the predominant contribution of hydrophobic (at high DA) and electrostatic (at low DA) interactions between chitosan monomers and the lecithin-covered droplet surface.

Understanding the electrokinetic behavior of the acrylic acid-based Fe(II) ion-imprinted polymer for its application in Fe(II) ions removal from aqueous medium with high selectivity

Understanding the electrokinetic behavior of the acrylic acid-based Fe(II) ion-imprinted polymer for its application in Fe(II) ions removal from aqueous medium with high selectivity

Electrokinetic behavior of a pH-regulated dielectric cylindrical nanopore

A continuum model is adopted to describe the electrokinetic behavior of a pH-regulated cylindrical nanopore, the surface of which has charge-regulated carboxyl groups. We focus on the influences of the permittivity of the nanopore material, nanopore size, salt concentration, and solution pH on this behavior, and the underlying mechanisms. The influence of the nanopore permittivity becomes significant when a nanopore is shorter than ca. 50 nm. It is interesting to observe that if it is longer than ca. 100 nm, the nanopore conductance decreases with increasing permittivity. If it is sufficiently short, the conductance increases with increasing permittivity. If the nanopore length takes a medium level, the conductance is insensitive to the variation in the permittivity. For a short nanopore (~20 nm), the conductivity increases with increasing permittivity. However, if pH is sufficiently high, it becomes insensitive to permittivity. Although the larger the permittivity the greater the conductivity, in general, this effect becomes insignificant when the bulk salt concentration is sufficiently high, implying that the effect of membrane polarization is important only if the bulk salt concentration is sufficiently low.

Electrokinetic and gel behavior of Si3N4 aqueous suspension

Electrokinetic and gel behavior of Si3N4 aqueous suspension for gel casting were investigated in this study. The zeta potential of dilute and concentrated suspension with organic binder was evaluated innovatively. The influence of the binder composition and solid loading on the gel time and viscosity of the slurry was studied. The result showed that absolute value of zeta potential would be lower in the concentrated suspension or suspension with organic binder. The release of NH3 during ball milling would increase the pH value, while the dissociation of the soluble SiO2 would increase it during setting. The gel time of the suspension was significantly affected by the organic binder addition. Higher pH value and lower solid loading was conductive to obtain slurry with lower viscosity.

A fundamental assessment of the impacts of cation (Cd, Co, Fe) substitution on the molecular chemistry and surface reactivity of sphalerite

A series of cadmium-, cobalt-, and iron-substituted (0–4 wt%) sphalerite mineral samples were synthesised to test how the presence of these cation substituents alter the crystal structure, surface bonding environment and electronic properties of sphalerite and to illustrate how these alterations impact the electrokinetic behaviour of mineral surfaces under conditions relevant to sphalerite flotation. A combination of X-ray Diffraction (XRD), Raman and ultraviolet–visible spectroscopies, and zeta potential experiments were used to demonstrate these impacts. XRD results showed a positive correlation between the measured lattice distortions and the ionic size and concentration of the respective cation substituents. Raman results confirmed the presence of new metal-sulphur (M−S) bonds within the ZnS host cluster reflected by a new impurity mode which correlates to the concentration and chemical nature of the cation substituents. The presence of metal substituents further induced a change in the band gap of sphalerite which reduced according to Cd > Fe > Co. These measurements informed the effect of the molecular characteristics of impurity-bearing sphalerite on the electrokinetic response of sphalerite in the presence of CuSO4 and xanthate collector. Cobalt-bearing sphalerites which have the lowest band gap and greatest distortions to molecular and crystal structure had the most notable impact on zeta potential measurements. A small increase in Co concentration induced a larger shift in point of zero charge for collectorless activation but did not impact the collector interactions. Conversely, Cd which has a wider band gap is less electronegative than Co exhibited the reverse behaviour. This study thus details how the presence of cation substituents modifies sphalerite bulk structure, in turn impacting its surface bonding environment and electronic properties, and ultimately exerting a notable control on flotation chemistry.

Electrokinetic characterization of synthetic protein nanoparticles.

The application of nanoparticle in medicine is promising for the treatment of a wide variety of diseases. However, the slow progress in the field has resulted in relatively few therapies being translated into the clinic. Anisotropic synthetic protein nanoparticles (ASPNPs) show potential as a next-generation drug-delivery technology, due to their biocompatibility, biodegradability, and functionality. Even though ASPNPs have the potential to be used in a variety of applications, such as in the treatment of glioblastoma, there is currently no high-throughput technology for the processing of these particles. Insulator-based electrokinetics employ microfluidics devices that rely on electrokinetic principles to manipulate micro- and nanoparticles. These miniaturized devices can selectively trap and enrich nanoparticles based on their material characteristics, and subsequently release them, which allows for particle sorting and processing. In this study, we use insulator-based electrokinetic (EK) microdevices to characterize ASPNPs. We found that anisotropy strongly influences electrokinetic particle behavior by comparing compositionally identical anisotropic and non-anisotropic SPNPs. Additionally, we were able to estimate the empirical electrokinetic equilibrium parameter (eEEEC) for all SPNPs. This particle-dependent parameter can allow for the design of various separation and purification processes. These results show how promising the insulator-based EK microdevices are for the analysis and purification of clinically relevant SPNPs.

Antimicrobial Properties of Composites of Chitosan-Silver Doped Zeolites

The antimicrobial functionality of composites constituted by chitosan with silver-doped zeolites was developed and characterized. A composite with chitosan particles and silver-doped zeolites was synthesized using an ionic gelation process with sodium tripolyphosphate. The chitosan silver-doped zeolites composite obtained presented sizes up to 5 μm, while the silver-doped zeolites had an average size between 0.5 μm and 3.3 μm. The synthesized chitosan silver-doped zeolites composites, as well as the silver-doped zeolites and the chitosan dissolution, were characterized through X-ray diffraction, Fourier Transform Infrared spectroscopy and scanning electron microscopy. The electro kinetic behaviour of chitosan, silver-doped zeolites and chitosan silver-doped zeolites composite was evaluated under different pH conditions. The antimicrobial activity of the composites was evaluated in terms of minimum inhibitory concentrations and minimum lethal concentrations and the results suggest that the chitosan silver-doped zeolites composites show antimicrobial activity against gram-negative and gram-positive bacteria, Escherichia coli and Staphylococcus aureus, respectively and against Candida albicans. The results here presented support the potential application of the composite of chitosan with silver-doped zeolites in the functionalization of textiles with antimicrobial properties.

Electrokinetic behavior of bullet-shaped nanopores modified by functional groups: Influence of finite thickness of modified layer

We examined theoretically the electrokinetic behavior of a bullet-shaped nanopore modified by a functional layer, focusing on the influence of its thickness. The nanopore contains both fixed surface charge coming from the original bare surface, and space fixed charge from the modified layer. The results of numerical simulation reveal that the presence of this layer is crucial to the electrokinetic behavior of the nanopore. In particular, its softness is capable of influencing ionic profiles through electroosmotic flow (EOF). Unlike a conical nanopore where its surface normal vector is constant, that of the present bullet-shaped nanopore varies along the pore axis, thereby affecting the degree of EOF, which in turn, can make the ionic profile inside the modified layer more uniform. This is crucial to the applications of the nanopore, for example, in mimicking biological membranes and sensing metal ions.

Lanthanum enriched TiO2-ZrO2 hybrid material with tailored physicochemical properties dedicated to separation of lithium and cobalt(II) raising from the hydrometallurgical stage of the recycling process of lithium-ion batteries

The paper presents the conceptual separation process of lithium and cobalt(II) ions from aqueous solution using lanthanum enriched TiO2-ZrO2 hybrid material. The material was synthesized via modified sol-gel method and thoroughly characterized with respect to porous structure, morphology, chemical composition, nature of characteristic functional groups, crystallinity and electrokinetic behaviour. Furthermore, sorptive properties of the obtained hybrid material were indicated towards recovery of lithium and cobalt(II) ions. The influence of such parameters as sorption time, temperature, adsorbate concentration, adsorbent dose and solution pH, on the efficiency of the performed adsorption process was determined. Experimental data collected have shown a high selectivity of the synthesized hybrid material relative to cobalt(II) ions in the presence of lithium ions.

Effect of solvent polarity during electrodeposition of asphaltenes from a Colombian oil in the presence of a magnetic field and magnetic nanoparticles

This work focuses on analyzing the electrokinetic behavior of asphaltenes of extra heavy oil. For this, electrodepositions were carried out in asphaltene solutions (4 %w/w) with two solvents of different polarities: toluene and chloroform. In addition, we worked with different magnetic fields, and the effect of adding 1% w/w of magnetic nanoparticles was analyzed. The asphaltenes were extracted with heptane and were characterized by infrared and ultraviolet visible spectroscopy. In the case of toluene, the initial adsorption (without fields) was 4 mg in both anode and cathode. By using an electric field (100 V/m) the deposits increased to 6 mg (anode) and 5 mg (cathode). However, when using a static magnetic field of 0.1 mT, no changes were observed. But, by modifying said field by a dynamic one (0.1 mT and 60 Hz), 15 mg (anode) and 19 mg (cathode) were obtained. Moreover, the addition of nanoparticles (previously characterized by scanning electron microscopy and X ray diffraction) changed the behavior, worsening in the absence of fields, and improving only in the presence of the dynamic field (104 mg, 26 mg in anode and cathode, respectively). Similar results were obtained when using chloroform. Thus, the best performance was obtained by using a dynamic magnetic field. By not considering the nanoparticles, total deposits increased more than 14 times (102 mg versus 7 mg). However, considering them, the increase was greater than 30 times (302 mg versus 10 mg). Therefore, we consider that adding nanoparticles, and supporting the electrodeposition process with a dynamic magnetic field, is an alternative that must be included to improve process performance.

Overlimiting behavior of surface-modified heterogeneous anion-exchange membranes

Electrochemical and electrokinetic behavior of ion-exchange systems as a result of electrostatic interactions between the fixed charge and the ionic species present in the electrolyte can significantly vary with the type of electrolyte and the membrane composition. In this paper, we studied experimentally the effect of surface modification of a heterogeneous anion-exchange membrane on its properties and overlimiting behavior. The surface modification of the anion-exchange membrane included carboxylation of its surface through benzophenone-based photochemistry followed by covalent linkage of single stranded DNA molecules. Such surface chemistry produced molecular layers of negative charge on the positively charged membrane surface. We investigated the membrane samples with different two levels of surface modification after their exposure either to KCl solutions or solutions containing a biopolymer serving as a model membrane foulant. The surface modification resulted in larger system resistances that were especially pronounced in the limiting and overlimiting region. Water splitting reaction on both the pristine and the modified membranes occurred approximately to the same extent. Unlike water splitting, electroconvection, as another mechanism driving overlimiting current, tracked by the PIV method was largely suppressed upon surface modification especially with DNA molecules. The membranes with the chemically modified surfaces showed smaller susceptibility towards fouling.