Mechanism of hydrolyzable metal ions effect on the zeta potential of fine quartz particles

The effects of ion species, cation valence, ionic strength, and hydrated ionic radius on the zeta potential of quartz have been systematically studied through the measurement of zeta potential, sedimentation rate, and aggregation observation. The results show that the interaction between hydrolysis components and quartz particles results in three critical points – CR₁, CR₂, and CR₃. The results of sedimentation and aggregation observation are in good agreement with the changes of the zeta potential in 0.1?M MgCl₂, the maximum sedimentation rate being 99.26% at pH 10.85. When the pH is around 6.25 or 10.00, the sedimentation rate is relatively lower and the size of aggregation smaller. The adsorption of hydrolyzable multivalent metal ions on the quartz surface is a combination of three adsorption forms, namely electrostatic adsorption, hydroxyl complex adsorption, and hydroxide precipitation adsorption. Then the hydrolysis properties of metal ions and the surrounding environment determine the action of the hydrolysis components and the main form of adsorption.     

Effect of dispersants on dispersion stability of collophane and quartz fines in aqueous suspensions

A stable dispersion of fine mineral particles in an aqueous system facilitated by dispersants is an essential prerequisite for their successful separation. We investigated the dispersion stability and mechanism of suspensions of aqueous collophane and quartz fines (10?µm) in the presence of sodium hexametaphosphate (SHMP), sodium silicate or sodium carbonate using the sedimentation balance method, zeta potential measurements, contact angle measurements, micro-flotation tests and theoretical calculation of Extended-DLVO (Derjaguin-Landau-Verwey-Overbeek). The results showed that three dispersants significantly enhanced the dispersion stability of collophane in the following descending order SHMP?>?sodium silicate?>?sodium carbonate. This is because they increased the zeta potential of collophane in the same order; meanwhile, the SHMP made the collophane more hydrophilic compared to two other dispersants. These results illustrated that the dispersion stability was attributed to electrostatic repulsion and hydration repulsion and that the hydration repulsion had a greater influence on the stability than electrostatic repulsion based on the calculation of Extended-DLVO. However, the quartz suspension always maintained a stable dispersion in the absence or presence of dispersants, since there was a higher zeta potential and stronger hydrophilicity for natural quartz. These provide a theoretical direction for the dispersion of fine-disseminated siliceous phosphorites and phosphate slimes in separations.     

On the electrophoretic mobility and zeta potential of montmorillonite in non-aqueous media

Experimental results on the electrophoretic velocity and mobility of Ca-montmorillonite in 2-propanol are reported. The variation of the electrophoretic velocity with the externally applied electric field and the particle size range, at constant volume fraction and temperature, is considered. Given the difficulties for determining the types and concentrations of ions present in these liquid media, two methods are discussed for the estimation of the double layer thickness and hence the product, necessary for the determination of the zeta potential () of the interface. Although both methods of calculation yield different values of, the results for the zeta potential are very similar in the regions of and characteristic of our systems. The application to the experimental data of three theoretical relations between electrophoretic mobility and zeta potential is also discussed.     

On the asymmetry of thermodynamic fluctuations of the electrode potential

The asymmetry of thermodynamic fluctuations of the equilibrium electrode potential and the asymmetry of thermodynamic fluctuations of the electrical double layer charge is characterized quantitatively on the basis of third-order noise spectra.Translated from Elektrokhimiya, Vol. 41, No. 2, 2005, pp. 131–136.Original Russian Text Copyright © 2005 by Grafov.This revised version was published online in April 2005 with corrections to the article note and article title and cover date.     

Effect of Discrete Macroion Charge Distributions on Electric Double Layer of a Spherical Macroion

The effect of replacing the conventional uniform macroion surface charge density with discrete macroion charge distributions on the structure of electric double layer (EDL) of a spherical macroion has been investigated by Monte Carlo (MC) simulations. Two discrete models have been investigated in addition to the central macroion charge: point charges localized on the macroion surface and finite-sized charges protruding into the solution. Both models have been studied with fixed and mobile macroion charges. The radial functions of local densities and electrostatic potential in EDL, are calculated and compared to the results obtained for the central macroion charge distribution. It is concluded that the model of charge distribution significantly affects the EDL structure close to the macroion, while the effect is much weaker at larger distances. With point charges localized on the macroion surface, counterions become stronger accumulated to the macroion, as a result the absolute values of surface potential ?₀ and zeta ξ potential are decreased. With protruding charges, the excluded volume effect dominates over the increased correlation ability; hence the counterions are less accumulated near the macroions and the absolute values of ?₀ and ξ potentials are increased.     

Phase diagram of alloy crystal in the exhaustively deionized suspensions of binary mixtures of colloidal spheres

Phase diagrams of liquidlike, alloy crystal-like and amorphous solid-like(AS) structures have been obtained for the exhaustively deionized aqueous suspensions of the binary mixtures of polystyrene or silica spheres. Diameter, polydispersity index (standard deviation of diameter divided by the mean diameter) and size ratio of the binary spheres (diameter of small sphere divided by that of large one) range from 85 to 136 nm, 0.07 to 0.26 and 0.76 to 0.93, respectively. Close-up color photographs of the alloy crystals are taken and the crystal structure has been analysed from reflection spectroscopy. Most of the alloy crystals aresubstitutional solid-solution (sss) type and body-contered cubic lattice structure. Formation of the alloy crystals is attributed to the important role of the expanded electrical double layers in the deionized condition and increase toward unity in the effective size ratio, which is the effective diameter of small sphere including double layer divided by that of large sphere AS structure is formed at the rather high concentrations of two spheres, where the thickness of the electrical double layer is thin and the effective size rado is comparatively small.     

An Application of Functional Analysis Method to the Potential of Electrical Double Layer for Spherical Micelles

With the help of the iterative method in functional analysis theory based on the Gouy–Chapman model in the colloid and interface chemistry an analytic solution of the potential of electrical double layer of spherical micelles has been obtained. This method has eliminated the restriction that the Poisson–Boltzmann equation, which represents the distribution of the potential in the double layer, can be solved only under the condition of zekT so far. The connections between the present results and those from Verwey and Overbeek's previous work have also been discussed. Our approach provides a simple but effective method for the calculation of the potential of electrical double layer under general potential condition.     

The Isoelectric Point of an Exotic Oxide: Tellurium (IV) Oxide

The pH-dependent surface charging of tellurium (IV) oxide has been studied. The isoelectric point (IEP) of tellurium (IV) oxide was determined by microelectrophoresis in various 1-1 electrolytes over a concentration range of 0.001–0.1 M. In all electrolytes studied and irrespective of their concentration the zeta potential of TeO₂ was negative over the pH range 3–12. In other words the IEP of TeO₂ is at pH below 3 (if any). TeO₂ specifically adsorbs ionic surfactants, and their presence strongly affects the zeta potential. In contrast the effect of multivalent inorganic ions on the zeta potential of TeO₂ is rather insignificant (no shift in the IEP). In this respect TeO₂ is very different from metal oxides.     

Frequency dependence of the dielectric and electro-optic response in suspensions of charged rod-like colloidal particles

We have performed an experimental investigation on the electrokinetic properties of charged rod-like fluorinated latex colloids. Systematic measurements of electrophoretic mobility, dielectric constant and electric birefringence have been performed as a function of the concentration of added nonionic surfactant and salt. In the investigated range of parameters, the zeta potential is a strongly decreasing function of the concentration of nonionic surfactant, while it is basically independent from ionic strength. We have obtained the frequency dependence of dielectric constant and Kerr constant as a function of zeta-potential and ionic strength. We observe the transition from a low frequency behavior, where both the dielectric constant and the Kerr constant are enhanced by the presence of the double layer, to a high frequency behavior, where both quantities take the value expected for unchanged particles in an insulating medium. The shape of the frequency dispersion of the Kerr constant coincides with that of the dielectric constant, but the cut-off frequencies are the same only when the zeta-potential of the particles is low.     

Effects of Ethanol on the Stability of Pigment Colloidal Dispersion

The effects of ethanol on the thickness and ionization of adsorbed polymer layer on pigment were investigated. The results showed that the thickness of adsorbed polymer layer decreased with the increase of the ethanol concentration, and then the pigment particles aggregated when the concentration of ethanol is higher than 40%. The zeta potentials became more negative with the increasing of the ethanol concentration, and then changed reversely when the ethanol concentration was higher than 16%. The thickness and structure of adsorbed polymer layer on the particle determined the stability of pigment dispersion.     

Diffusiophoresis of an Elongated Cylindrical Nanoparticle along the Axis of a Nanopore

The translation of a charged, elongated cylindrical nanoparticle along the axis of a nanopore driven by an imposed axial salt concentration gradient is investigated using a continuum theory, which consists of the ionic mass conservation equations for the ionic concentrations, the Poisson equation for the electric potential in the solution, and the modified Stokes equations for the hydrodynamic field. The diffusiophoretic motion is driven by the induced electrophoresis and chemiphoresis. The former is driven by the generated overall electric field arising from the difference in the ionic diffusivities and the double layer polarization, while the latter is generated by the induced osmotic pressure gradient around the charged particle. The induced diffusiophoretic motion is investigated as functions of the imposed salt concentration gradient, the ratio of the particle’s radius to the double layer thickness, the cylinder’s aspect ratio (length/radius), the ratio of the nanopore size to the particle size, the surface charge densities of the nanoparticle and the nanopore, and the type of the salt used. The induced diffusiophoretic motion of a nanorod in an uncharged nanopore is mainly governed by the induced electrophoresis, driven by the induced electric field arising from the double layer polarization. The induced particle motion is driven by the induced electroosmotic flow, if the charges of the nanorod and nanopore wall have the same sign.     

Accounting for the Adsorption of Anions When Interpreting the Mechanism of Electrodeposition of Metals from Complex Electrolytes: The Reaction Order by the Electrochemically Active Ion

The relationship between the current and the bulk concentration of complex ions during concurrent specific adsorption of an electrochemically active complex ion and a complexing ligand is considered. The effect of parameters that characterize adsorption of such ions and the structure of the electrical double layer on this relationship is analyzed.__________Translated from Elektrokhimiya, Vol. 41, No. 7, 2005, pp. 817–822.Original Russian Text Copyright © 2005 by Rogozhnikov.     

The zeta potential of kaolin suspensions measured by electrophoresis and electroacoustics

The zeta potentials of kaolin dilute and concentrated suspensions were monitored using the techniques of electrophoresis and electroacoustics, respectively. The effect of addition of salt (KCl), a polymer material (Triton X-100), and an anionic surfactant (sodium dodecyl sulphate, SDS) on the suspension properties was investigated by electrophoresis. Electroacoustics was employed for the measurement of zeta potentials for the highest possible kaolin content in suspension and the effect of dilution. The effect of aging of a freshly prepared sample and kaolin isoelectric point was also studied. Using both techniques it was noted that there was no isoelectric point, just a maximum value in the magnitude of the kaolin suspension zeta potential. These maxima were observed also in the presence of Triton X-100 and SDS. An increase of the concentration of KCl and SDS in suspension shifted the maxima towards more acidic values, while in the presence of Triton X-100 the position of the zeta potential maxima remained constant. Electroacoustic techniques revealed that a freshly prepared concentrated suspension requires about six hours to equilibrate to achieve a steady zeta potential. Diluting the concentrated suspensions led to decrease of the zeta potential as ions bound to the surface desorbed and screened the surface charge. The zeta potential maxima remained unchanged even after heating the powder in an oven at 200°C (to remove any organic material) thereby suggesting that the most likely explanation for the maxima is isomorphic substitution.     

Mechanism of metals’ electrodeposition from complex electrolytes allowing for the anions’ adsorption: Effect of the position of ligands and complex ions in the compact layer on the reaction orders

Effect of the relative position in the compact layer of specifically adsorbed electroactive complex ion and complexing ligand on the magnitude of current is considered. Effect of parameters that characterize the adsorption of such ions and the electrical double layer structure on the dependence of current on the solution composition and effective reaction orders is analyzed.     

Experimental determination of energy barrier to particle detachment

The estimation of energy barrier to detachment of particles from a substrate was carried out. Detachment processes of 4 m polyethylene particles from a quartz wall under the gravitational force in aqueous solutions were investigated by a direct observation technique. The magnitude of energy barriers was experimentally determined by the temperature dependence of the rate constant of detachment and was compared with that estimated theoretically from the superposition of electrostatic and London—van der Waals energies calculated using the experimental electrokinetic potentials and Hamaker constants, respectivley. Both were in fairly good agreement.     

盐浓度及磷脂分子结构对多组分带电膜弯曲刚性的影响

磷脂膜弯曲刚性模量很难直接测量, 本实验用循环冻融法制备尺寸大小与膜弯曲刚性相关的熵稳定单层囊泡. 粒度仪测量发现, 囊泡尺寸随盐浓度增加呈现先剧烈减小然后缓慢增加的分段变化规律. 但当组分中含有头部带电同时尾链带有不饱和键的二油酰磷脂酰甘油酯时, 囊泡尺寸却在较大的盐浓度范围内不出现回升. 囊泡膜的负Zeta-电势绝对值均表现为先急剧减小然后趋于平稳的变化规律, 数值大小只与带电组分的含量有关. 而对直接水合法制备的多层囊泡的统计发现, 囊泡尺寸随盐浓度增加急剧减小, 随后趋于稳定值, 均不随分子组合变化而回升. 结果表明在不同的盐浓度范围里, 主导磷脂膜弯曲刚性模量的因素不同. 低盐浓度的体系, 静电屏蔽效应为主导因素; 高盐浓度的体系, 膜双电层中反离子的分布起主导作用. 磷脂分子头部与尾部的不同结构组合会影响膜双电层, 使膜的弯曲刚性不同. 多层囊泡体系中, 高盐浓度下膜的热涨落掩盖了分子结构及双电层分布差异对膜弯曲刚性的影响.     

Effect of the diffuse double layer on the interpretation of EQCM results in dilute NaClO4 solutions

The response of the electrochemical quartz crystal microbalance (EQCM) in dilute NaClO₄ solutions was studied with gold and iron electrodes during a stepwise increase of the perchlorate concentration. In the range from 10⁻⁴ M to 7.8×10⁻² M, the quartz resonant frequency of the 10 MHz AT cut crystals increased by about 700 Hz, indicating a mass loss on the electrode. A model was developed in which the diffuse double layer and the oscillating bulk electrolyte layer, characterised by the velocity decay length of the damped shear wave in solution, are treated as two independent, superimposed sheets. By assuming a characteristic thickness of the diffuse double layer according to the Gouy–Chapman theory and by treating the diffuse double layer as a rigid sheet, the measured mass loss could be simulated qualitatively. The viscosity changes in the diffuse double layer as well as in the sensed electrolyte bulk layer were found to be negligible in the concentration range investigated. In dilute solutions, the frequency shift following a concentration change is entirely due to thinning of the diffuse double layer with increasing concentration. The results demonstrate the importance of diffuse double layer effects for EQCM measurements in dilute electrolytes.     

The change in thickness of the solidified liquid layer rather than the immobilized mass determines the frequency response of a quartz crystal microbalance

The "solidified liquid layer" model has been examined using a quartz crystal microbalance(QCM) with a polymeric matrix.The model is shown to give a reasonable explanation for the following experimental observations:(i) The opposite response of the QCM and surface plasmon resonance(SPR) for the activation process;(ii) the marked difference in the responses for IgG/anti-IgG interaction between QCM and SPR.Theoretical analysis and experimental results indicated that QCM is sensitive to the thickness change of the "solidified liquid layer" but not the mass of captured biomolecules(i.e.,the immobilized mass),implying caution must be taken in interpreting QCM results.     

Rheological properties of deionized Chinese ink

Rheological properties for Chinese ink in exhaustively deionized aqueous media were carefully examined. In the steady shear measurement, the shear viscosities of the ink could be well explained by considering the “effective” volume fraction of the particles in the ink including the electrical double layers and by using Einstein's equation for dilute suspension viscosity, when the particle volume fraction was substantially low. In the case that the volume fraction was higher, the shear viscosities showed extremely higher than those from Einstein's prediction, though the ink remained a Newtonian liquid. In the stress-strain measurement, the shear moduli were observed at strain smaller than 0.2. The “weak” aggregation among the particles in the ink under no shear or low shear rates was supported. It should be noted that the glue in the suspension plays an important role for the good liquidity of the ink and for the “weak” bridges among the particles resulting its good dispersion stability.     

Effect of Electrolyte Concentration on the Stern Layer Thickness at a Charged Interface

The chemistry and physics of charged interfaces is regulated by the structure of the electrical double layer (EDL). Herein we quantify the average thickness of the Stern layer at the silica (SiO₂) nanoparticle/aqueous electrolyte interface as a function of NaCl concentration following direct measurement of the nanoparticles’ surface potential by X‐ray photoelectron spectroscopy (XPS). We find the Stern layer compresses (becomes thinner) as the electrolyte concentration is increased. This finding provides a simple and intuitive picture of the EDL that explains the concurrent increase in surface charge density, but decrease in surface and zeta potentials, as the electrolyte concentration is increased.