Electrokinetic Properties Research Articles

A dsDNA model optimized for electrokinetic applications.

We present a coarse-grained (CG) model of a charged double-stranded DNA immersed in an electrolyte solution that can be used for a variety of electrokinetic applications. The model is based on an earlier rigid and immobile model of Weik et al. and includes now semi-flexibility and mobility, so that DNA dynamics can be sufficiently captured to simulate a full nanopore translocation process. To this end we couple the DNA hydrodynamically via a raspberry approach to a lattice-Boltzmann fluid and parametrize the counterions with a distant dependent friction. The electrokinetic properties of the CG DNA model inside an infinite cylinder is fitted against experimental data from Smeets et al. and all-atom simulation data from Kesselheim et al. The stiffness of our CG DNA is modeled via a harmonic angle potential fitted against experimental data of Brunet et al. Finally, the quality of our tuned parameters is tested by measuring the electrophoretic mobility of our DNA model for various numbers of base pairs and salt concentrations. Our results compare excellently with the experimental data sets of Stellwagen et al. and Hoagland et al.

How side chains affect conformation and electrical properties of poly(acrylic acid) in solution?

To better understand the effect of side chains on the chain conformation and electrical properties of polyelectrolytes, dielectric measurements were carried out on solutions of poly(acrylic acid) (PAA), poly(acrylic acid)-graft-dodecyl (PAA-g-dodecyl), and poly(acrylic acid)-graft-poly(ethylene oxide) (PAA-g-PEO) over a wide concentration range. Double dielectric relaxations with counterion distribution were observed for these polymers and a refined double-layer polarization model was proposed to analyze these, by which valuable information about conformations and interfacial electrokinetic properties was obtained. The transitional concentrations for the overlapping and entanglement of chains were identified from results for the dielectric increment and relaxation time. The concentration dependences of the ratio of effective charges were estimated from conductivity data. It was shown that effective charges on PAA were greatly influenced by PEO or dodecyl side chains, which caused steric hindrance of counterion binding and further dissociation of carboxylic groups or bound counterions. Moreover, a mutual superposition and offsetting effect of PEO and dodecyl side chains was observed. An enhancement in the interpenetration of counterion atmospheres as a result of side chains was also found. In addition, the rate constant ratio and the distance of counterion fluctuations perpendicular to the chains were estimated. It was demonstrated that the effects of side chains on the effective charges or ionization properties of GCP play an important role in their conformation, counterion distribution, and fluctuation.

Electromigration properties of capillary columns with polystyrene coating as a stationary phase

Relationships in variation of the surface energy of polystyrene coatings on melted quartz at varied polymer concentration in solution were refined by studying the functional chemical composition and surface structure of model coatings of atactic polystyrene on quartz plates and the electromigration properties of capillary columns with polystyrene coatings. The optimum concentration and temperature-kinetic conditions for preparing polystyrene coatings on quartz capillaries with controllable electrokinetic properties were determined.

Adipose Stem Cells Display Higher Regenerative Capacities and More Adaptable Electro-Kinetic Properties Compared to Bone Marrow-Derived Mesenchymal Stromal Cells.

Adipose stem cells (ASCs) have recently emerged as a more viable source for clinical applications, compared to bone-marrow mesenchymal stromal cells (BM-MSCs) because of their abundance and easy access. In this study we evaluated the regenerative potency of ASCs compared to BM-MSCs. Furthermore, we compared the dielectric and electro-kinetic properties of both types of cells using a novel Dielectrophoresis (DEP) microfluidic platform based on a printed circuit board (PCB) technology. Our data show that ASCs were more effective than BM-MSCs in promoting neovascularization in an animal model of hind-limb ischemia. When compared to BM-MSCs, ASCs displayed higher resistance to hypoxia-induced apoptosis, and to oxidative stress-induced senescence, and showed more potent proangiogenic activity. mRNA expression analysis showed that ASCs had a higher expression of Oct4 and VEGF than BM-MSCs. Furthermore, ASCs showed a remarkably higher telomerase activity. Analysis of the electro-kinetic properties showed that ASCs displayed different traveling wave velocity and rotational speed compared to BM-MSCs. Interestingly, ASCs seem to develop an adaptive response when exposed to repeated electric field stimulation. These data provide new insights into the physiology of ASCs, and evidence to their potential superior potency compared to marrow MSCs as a source of stem cells.

Homogeneous gold nanoparticle monolayers—QCM and electrokinetic characteristics

Deposition mechanism of gold nanoparticles on poly(allylamine chloride) (PAH)-modified silica and mica was investigated by the quartz crystal microbalance (QCM), scanning electron microscopy (SEM), atomic force microscopy (AFM) and streaming potential measurements (SP). The influence of the suspension concentration, ionic strengths and pH was studied. It was shown that the particle deposition was irreversible that enabled to precisely determine the maximum coverage of monolayers. The experimental results were quantitatively interpreted in terms of the random sequential adsorption (RSA) model where the bulk and surface transfer steps were considered in a rigorous way. The results obtained by QCM were exploited as reference data for interpreting the streaming potential (SP) measurements of gold nanoparticle monolayer formation at PAH-modified mica. In these experiments the coverage of particles was determined via SEM and AFM imaging of monolayers. This allowed to quantitatively interpret the zeta potential vs. particle coverage dependencies derived from SP measurements in terms of the general electrokinetic model without using adjustable parameters. In this way, a functional dependence was specified for calculating the nanoparticle coverage in situ. Additionally, by using the SP measurements, thorough electrokinetic characteristics of gold nanoparticle monolayers were acquired. They comprised the dependence of the monolayer zeta potential on ionic strength (for a fixed pH) and the acid-base characteristics of monolayers, derived in pH cycling experiments carried out at fixed ionic strength. It was concluded that these results enable to develop a reproducible method for preparing gold nanoparticle monolayers of controlled coverage and well-characterized electrokinetic properties with potential application as protein adsorption platform.

Influence of the electrokinetic properties of cellulose on the morphology of iron(III) oxide upon template synthesis

Microsized tubes and fibers of iron(III) oxide are obtained by the sol-gel method using cotton cellulose as template. The influence of the electrokinetic properties of the surface of cotton cellulose and sols of nanoparticles, as well as the calcination temperature on morphology and the properties of ceramic fibers, is studied. It is noted that the use of sol with a strongly acidic dispersion medium leads to the formation of microtubes, fully repeating the features of the structure of the original cellulose fiber. The mechanism of the formation of fibers and tubes based on electrostatic interactions is proposed. With an increase of the calcination temperature from 600 to 1200°C, there is an increase in the size of the α-Fe2O3 particles, a reduction of the inner diameter of the tubes, and an increase of their mechanical strength.

Effect of mono- and bimetallic nanoparticles Fe, Ni, & Fe/Ni based on carbon nanocomposites on electrocatalytic properties of anodes

The optical properties of metallic Fe nanoparticles (NPs), Ni NPs and bimetallic Fe/Ni NPs produced under radiolysis in anaerobic condition based on a chemical reduction in the presence of oxygen and quercetin in reversed micellar solutions, and electrokinetic properties of nanoparticles carbon-based nanocomposites were studied. The possibility of the preparation of coating using different nanocomposites with anomalous electrocatalytic is addressed.

Colloidal Properties of Recombinant Spider Silk Protein Particles

Colloidal particles have been prepared from polyanionic and polycationic recombinant spider silk protein. The amino acid sequences of these spider silk proteins are identical except for 16 residues bearing either a cationic or an anionic ionizable group. Electrophoretic titration showed that protonation of the acidic and basic amino acids had significant impact on the electrophoretic mobility of the protein particles and, in particular, on their point of zero mobility (PZM). The experimentally determined PZMs are in good agreement with the theoretical values evaluated on the basis of the relevant amino acid sequences. A comprehensive description of the electrokinetic properties of the recombinant spider silk protein particles as a function of pH and solution ionic strength was provided from adequate application of electrokinetic theory for soft particles. Within the framework of this formalism, spider silk protein particles are viewed as porous colloids penetrable for ions and characterized by a finite penetration length for the electroosmotic flow. The differentiated electrokinetic properties of the particles were shown to be solely governed by the electrohydrodynamic features of their poorly charged outer peripheral layer with a thickness of about 10–20 nm. This finding was further corroborated experimentally by demonstrating that electrokinetics of particles bearing an additional outer layer consisting of oppositely charged spider silk proteins is entirely dominated thereby. The presence of a fuzzy, ion-permeable particle interface with an extension of several tenths of a nanometer was confirmed by direct measurement of the resulting steric forces using the colloidal probe atomic force microscopy (AFM) technique.

Structural, electrokinetic and surface properties of activated palygorskite for environmental application

Unlike smectite, the surface characteristics of palygorskite remain underexplored for its potential application in environmental remediation. In this study, palygorskite from Western Australia was activated through thermal (300°C for 4h), acid (4M HCl for 2h at 70°C) and acid-thermal (acid treatment followed by heating at 300°C for 4h) treatments, and the structural and physico-chemical characteristics were examined against the raw clay mineral. The influence of activation was systematically investigated using X-ray Diffraction (XRD), Fourier Transform Infra-Red (FTIR) spectroscopy, N2 adsorption-desorption measurements and solid state 27Al Magic Angle Spinning Nuclear Magnetic Resonance (MAS NMR) spectroscopy. The XRD patterns indicated preservation of the crystalline structure of palygorskite following all the treatments. These findings were supported by the Al (IV) and Al (VI) coordination peaks (chemical shift ~55 and 2.9ppm, respectively) which were unaltered in the 27Al MAS NMR spectra of the samples. The acid-thermal activated palygorskite exhibited the highest specific surface area (152.7m2g−1) and pore volume (0.2137cm3g−1) which respectively were 3-fold and 69% greater than the raw palygorskite. The potentiometric titration analyses highlighted the possible role of Al derivatives towards development of the surface charge of the activated palygorskites. Electrokinetic studies described the stability of the activated products (zeta potential values ranging from -5mV to -32mV) at different electrolyte (NaNO3) concentrations. Combined acid-thermal activated palygorskite displayed a stronger specific adsorption of multivalent cations, and held a direct relevance to environmental remediation. Findings of this study will assist in the development of palygorskite-based adsorbents for heavy metal contaminants remediation.

Dielectric Analysis for the Spherical and Rodlike Micelle Aggregates Formed from a Gemini Surfactant: Driving Forces of Micellization and Stability of Micelles.

The self-aggregation behavior of Gemini surfactant 12-2-12 (ethanediyl-1,2-bis(dimethyldodecylammonium bromide)) in water was investigated by dielectric relaxation spectroscopy (DRS) over a frequency range from 40 Hz to 110 MHz. Dielectric determination shows that well-defined spherical micelles formed when the concentration of the surfactant was above a critical micelle concentration CMC1 of 3 mM and rodlike micelles formed above CMC2, 16 mM. The formation mechanism of the spherical micelles and their transition mechanism to clubbed micelles were proposed by calculating the degree of counterion binding of the micelles. The interactions between the head groups and the hydrophobic chains of the surfactant led to the formation of the micelles, whereas the transition is mainly attributed to the interaction among the hydrophobic chains. By analyzing the dielectric relaxation observed at about 10(7) Hz based on the interface polarization theory, the permittivity and conductivity of micelle aggregates (spherical and clubbed) and volume fraction of micelles were calculated theoretically as well as the electrical properties of the solution medium. Furthermore, we also calculated the electrokinetic parameters of the micelle particle surface, surface conductivity, surface charge density, and zeta potential, using the relaxation parameters and phase parameters. On the basis of these results, the balance of forces controlling morphological transitions, interfacial electrokinetic properties, and the stability of the micelle aggregates was discussed.

The physicochemical properties of CTAB solutions in the presence of α-tocopherol

The electrolytic conductivity, electrophoretic mobility and zeta potential (LDV - laser Doppler velocimetry method) as well as the particles size distribution (DLS - dynamic light scattering method) were determined in the cetyltrimethylammonium bromide (CTAB) solutions (0.25–25.00mM) at different concentrations of α-tocopherol (0–11.6mM). The measurements were made at 25°C and 30°C. It was found that α-tocopherol (vitamin E) modifies the physicochemical properties of CTAB micellar solutions – the potential carrier of bioactive substances. The electrolytic conductivity of CTAB solutions was lowered by the addition of α-tocopherol. Particularly, the effect was observed in the concentration range 0.25–2.5mM, i.e. in the vicinity of CMC. The critical micelle concentration (CMC) of CTAB solutions determined from the conductivity data decreased with the increasing vitamin E content due to the mixed aggregates formation. At the same time the electrophoretic mobility and zeta potential increased as a result of higher degree of the mixed aggregates dissociation. This effect was observed for all surfactant concentrations at both temperatures. The hydrodynamic diameter of mixed CTAB/α-tocopherol particles increased from 7–8nm for the CTAB solutions to 50–60nm for those containing vitamin E. The information about the aggregates size and their electrokinetic properties can be useful in predicting the encapsulation of biomolecules in the surfactant micelles and their transport by different membranes.

Compensating for Electrode Polarization in Dielectric Spectroscopy Studies of Colloidal Suspensions: Theoretical Assessment of Existing Methods.

Dielectric spectroscopy can be used to determine the dipole moment of colloidal particles from which important interfacial electrokinetic properties, for instance their zeta potential, can be deduced. Unfortunately, dielectric spectroscopy measurements are hampered by electrode polarization (EP). In this article, we review several procedures to compensate for this effect. First EP in electrolyte solutions is described: the complex conductivity is derived as function of frequency, for two cell geometries (planar and cylindrical) with blocking electrodes. The corresponding equivalent circuit for the electrolyte solution is given for each geometry. This equivalent circuit model is extended to suspensions. The complex conductivity of a suspension, in the presence of EP, is then calculated from the impedance. Different methods for compensating for EP are critically assessed, with the help of the theoretical findings. Their limit of validity is given in terms of characteristic frequencies. We can identify with one of these frequencies the frequency range within which data uncorrected for EP may be used to assess the dipole moment of colloidal particles. In order to extract this dipole moment from the measured data, two methods are reviewed: one is based on the use of existing models for the complex conductivity of suspensions, the other is the logarithmic derivative method. An extension to multiple relaxations of the logarithmic derivative method is proposed.

Capillary electrophoretic profiling of wood-based oligosaccharides

A method based on direct UV-detection was developed for the qualitative and quantitative determination of oligosaccharides simultaneously separated by capillary electrophoresis (CE). Reference compounds consisting of five xylo- three manno- and five cello-oligosaccharides were concurrently measured in a highly alkaline solution without derivatization. Sodium and potassium cations were used in the electrolyte solution to adjust the electrokinetic properties of the oligomers by controlling the mobility of charged species and to improve the resolution in baseline separation. The quantification range extended from 25 to 125 mg/L with linear correlation \(\hbox {R}^{2}=0.986{-}0.997\) for all analytes other than xylobiose and cellobiose, for which the range was 50–200 mg/L (\(\hbox {R}^{2}=0.995\)). The CE method developed was further applied to determine oligosaccharides from hot-water extracts of a bleached birch and pine kraft pulp, in which the oligosaccharides typically exist as complex mixtures.

Acid-base and adsorption properties of the AlOOH 2D nanostructures as factors for regulating parameters of model biological solutions

We have studied the acid-base, adsorption, and electrokinetic properties of 2D nanostructures—agglomerates of pseudoboehmite (AlOOH) nanosheets 2–5 nm in thickness—that were synthesized from electro-explosive Al/AlN nanopowder. By the example of adsorption of anionic dye eosin and cationic dye methylene blue, it is found that the synthesized nanostructures have pronounced anion-exchange properties. It is shown that agglomerates of AlOOH nanosheets exhibit properties of a weak base when they are added to the biological model solutions (cell-culture medium and sodium phosphate buffer) and deionized water; in this case, an increase in pH in the media takes place both due to the release of the OH groups and the ionexchange adsorption. The possible impact of the synthesized AlOOH 2D nanostructures on the suppression of tumor-cell proliferation is considered via changes in the parameters (acidity and ionic composition) of their microenvironment.

Dependence of Shape and Geometry of Microelectrodes in Manipulating Polarizable Particles like DNA through Electro-kinetic Effects

<p>Recently electro-kinetics, namely AC electro-osmosis and dielectrophoresis have been judiciously utilised to manipulate movement of polarizable particles like DNA suspended in aqueous solution and placed between electrically fed microelectrodes. Researchers around the globe have tried to fabricate electrodes of different geometries to understand how electric field owing to sharpness of the electrodes has influenced the aforementioned electro-kinetic properties. In this review, we have presented a chronological development indesign of patterned electrodes used to align and trap DNA molecules in and around the electrodes. We have examined the pros and the cons of such geometry of the set of the micro-electrodes and also tried to provide a solution in terms of shape and sharpness of the electrode that would facilitate DNA molecules to bridge between the electrodes for further application of conducting DNA as molecular wire. </p>

Electrokinetic behavoir of chitosan adsorbed on o/w nanoemulsion droplets

Chitosans with different molecular weight and degree of acetylation (DA) were adsorbed onto lecithin stabilized nanoemulsion droplets at pH ∼4.7. The electrokinetic properties of the nanoemulsion were investigated by using dynamic light scattering. According to the experimental data, the isoelectric point (IEP) of the droplets in the suspension at the presence of oppositely charged chitosan, does not depend on the polyelectrolyte molecular weight (when DA of chitosan is lower than 32%). Due to the high charge density of these polymer chains and low surface charge density of the lecithin stabilized droplets, the chitosan molecules retain part of the condensed counterions upon the adsorption process. Thus, the registered electrophoretic mobility corresponding to the “effective”, and not “real”, the electrokinetic charge of the droplets covered by a polymer layer. The stability behavior of the nanoemulsion in the presence of chitosan with lower charge density is different, and the IEP and stabilization of the system are achieved at higher polymer concentration. The coincidence in the polyelectrolyte concentration corresponding to IEP and minimum stability of the nanoemulsion against coagulation agrees with the notion that the electrostatic interactions are predominant in the coating layer formation. In spite of the similar electrokinetic behavior of the droplets covered with chitosan with low DA and different molecular weight, the polymers have different biological activity which might be results from different charge density of the molecules. In the present study, we show that the electrical polarizability is a complex parameter that can allow to more detailed characterization of the electrical properties of the chitosan.

Electrokinetic, electrorheological and viscoelastic properties of Polythiophene-graft-Chitosan copolymer particles

Electrokinetic properties of Polythiophene-graft-Chitosan (PT-g-CS) copolymer were investigated by means of zeta (ζ)-potential measurements as a function of pH, electrolytes, surfactants, and temperature in aqueous medium. The ζ-Potential of pure PT was observed to enhance from +25mV to +36mV after grating with polycationic CS. Concomitantly, the isoelectric point of the pure PT shifted from 6.4 to 8.3. The ζ-Potential of PT-g-CS dispersion also shifted to more positive regions with increasing valency of the electrolytes and concentrations of cationic surfactant (cetyltrimethylammonium bromide). The ζ-Potential of PT-g-CS was determined to be +38mV which indicated colloidal stability in silicone oil (SO) medium. Electrorheological (ER) and viscoelastic measurements revealed that the PT-g-CS/SO system has elasto-viscous behavior under applied electric field strengths. The yield stress of the ER fluid was determined to be a function of the electric field strength in a power law form as τy=E1.55 which obey to the conduction model. Creep and creep-recovery tests revealed reversible non-linear viscoelastic deformations of %31<%40<%43 under E=1; 2 and 3kV/mm conditions.

Electrokinetic properties of bare and particles containing textile

Electrokinetic properties of bare and particles containing textile

What Is the Rate-Limiting Transport Factor in LiNi0.8Co0.15Al0.05O2 (NCA)?

LiNi0.8Co0.15Al0.05O2 (NCA) has been widely used as cathode in commercialized lithium-ion batteries (LIBs), but its fundamental electrokinetic properties such as interfacial and bulk transport, are poorly understood. In our previous study, diffusivity and conductivity of bulk NCA at different states of charge (SOC) have been investigated using dense single-phase pellets1. Based on that, we further attempt to understand the electrochemical charge-transfer kinetics at NCA/liquid electrolyte interface, and find out the rate-limiting transport factor of NCA cathode in LIBs. From Butler-Volmer equation, exchange current density jo can be utilized to evaluate the kinetics at solid/electrolyte interface. Thus, we applied two methods - electrochemical impedance spectroscopy (EIS) and potentiostatic intermittent titration technique (PITT) to study the exchange current density of NCA at different SOC using the same dense bulk pellets2. Primary results of these measurements are shown in Fig. 1. Exchange current density from PITT is found to decrease with increasing SOC, whose value is nearly 102smaller at high SOC (70 %) than that of pristine NCA. However, EIS results show discrepancy above 50 % SOC. Based on the PITT results from bulk pellets, relative contributions of bulk and interfacial transport of the particles can be modeled using Biot numbers Λ and time constant analysis. Fixing the acceptable overpotential as 0.1 V, the rate of bulk diffusion and interfacial reaction of the 5.6 um commercial spherical NCA particles are plotted as Fig. 2. With increasing SOC, the maximum C-rate decreases by almost 102 and Λ is of order 100 indicating the mixed-control kinetics. In other words, the interfacial reaction clearly becomes the rate-limiting kinetic step and thus determine the rate-performance of NCA. This work was supported as part of the North East Center for Chemical Energy Storage (NECCES), an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Basic Energy Sciences under Award # DE-SC0012583.

Electrokinetics of Carbonate/Brine Interface in Low-Salinity Waterflooding: Effect of Brine Salinity, Composition, Rock Type, and pH on ?-Potential and a Surface-Complexation Model

Summary Laboratory studies have shown that wettability of carbonate rock can be altered to a less-oil-wetting state by manipulation of brine composition and reduction of salinity. Our recent study (Mahani et al. 2015b) suggests that surface-charge alteration is likely to be the driving mechanism of the low-salinity effect in carbonates. Various studies have already established the sensitivity of carbonate-surface charge to brine salinity, pH value, and potential-determining ions in brines. However, in the majority of the studies, single-salt brines or model-carbonate rocks have been used and it is fairly unclear how natural rock reacts to reservoir-relevant brine as well as successive brine dilution; whether different types of carbonate-reservoir rocks exhibit different electrokinetic properties; and how the surface-charge behavior obtained at different brine salinities and pH values can be explained. This paper presents a comparative study aimed at gaining more insight into the electrokinetics of different types of carbonate rock. This is achieved by ζ-potential measurements on Iceland spar calcite and three reservoir-related rocks—Middle Eastern limestone, Stevns Klint chalk, and Silurian dolomite outcrop—over a wide range of salinity, brine composition, and pH values. With a view to arriving at a more-tractable approach, a surface-complexation model (SCM) implemented in PHREEQC software (Parkhurst and Appelo 2013) is developed to relate our understanding of the surface reactions to measured ζ-potentials. It was found that regardless of the rock type, the trends of ζ-potentials with salinity and pH are quite similar. For all cases, the surface charge was found to be positive in high-salinity formation water (FW), which should favor oil-wetting. The ζ-potential successively decreased toward negative values when the brine salinity was lowered to seawater (SW) level and diluted SW. At all salinities, the ζ-potential showed a strong dependence on pH, with positive slope that remained so even with excessive dilution. The sensitivity of the ζ-potential to pH change was often higher at lower salinities. The existing SCMs cannot predict the observed increase of ζ-potential with pH; therefore, a new model is proposed to capture this feature. According to modeling results, formation of surface species, particularly &amp;gt;CaSO4− and to a lower extent &amp;gt;CO3Ca+ and &amp;gt;CO3Mg+, strongly influence the total surface charge. Increasing the pH turns the negatively charged moiety &amp;gt;CaSO4− into both negatively charged &amp;gt;CaCO3− and neutral &amp;gt; CaOH entities. (Note that throughout this paper, the symbol &amp;gt; indicates surface complexes.) This substitution reduces the negative charge of the surface. The surface concentration of &amp;gt;CO3Ca+ and &amp;gt;CO3Mg+ moieties changes little with change of pH. Nevertheless, besides similarities in ζ-potential trends, there exist notable differences in terms of magnitude and the isoelectric point (IEP), even between carbonates that are mainly composed of calcite. Among all the samples, chalk particles exhibited the most negative surface charges, followed by limestone. In contrast to this, dolomite particles showed the most positive ζ-potential, followed by calcite crystal. Overall, chalk particles exhibited the highest surface reactivity to pH and salinity change, whereas dolomite particles showed the lowest.