Solubility of Potassium Acetate in Water, 2,2,2-Trifluoroethanol,Ethanol and Their Binary Mixtures at 288.15—333.15 K

The potassium acetate solutions are new potential working fluids for the closed-type reverse electrodialysis(RED) power generation system driven by thermal energy. In this paper, the solubilities of potassium acetate in water, 2,2,2-trifluoroethanol, ethanol and their binary mixtures were measured by using the laser dynamic method over the temperature range of 288.15 to 333.15 K under atmospheric pressure. The results indicate that the solubility of potassium acetate solution is influenced by both the solvent components and solution temperature evidently. Besides, it is found that the measured solubility data of the potassium acetate-water-2,2,2-trifluoroethanol solutions as per the laser dynamic method are slightly larger than that of the data obtained as per the static method. Finally, five correlation models, including the Van't Hoff model, Modified Apelblat model, Yaws model, λh model and Modified Apelblat-Jouyban-Acree model, were used to correlate the measured solubility data of those potassium acetate solutions, with the relative standard deviations within 0.23% to 1.58%.     

Effect of surface morphology on membrane fouling by humic acid with the use of cellulose acetate butyrate hollow fiber membranes

A serious problem faced during the application of membrane filtration in water treatment is membrane fouling by natural organic matter (NOM). The hydrophilicity, zeta potential and morphology of membrane surface mainly influence membrane fouling. The aim of the present study is to reveal the correlation between membrane surface morphology and membrane fouling by use of humic acid solution and to investigate the efficiency of backwashing by water, which is applied to restore membrane flux. Cellulose acetate butyrate (CAB) hollow fiber membranes were used in the present study. To obtain the membranes with various surface structures, membranes were prepared via both thermally induced phase separation (TIPS) and nonsolvent-induced phase separation (NIPS) by changing the preparation conditions such as polymer concentration, air gap distance and coagulation bath composition. Since the membrane material is the same, the effects of hydrophilicity and zeta potential on membrane fouling can be ignored. More significant flux decline was observed in the membrane with lower humic acid rejection. For the membranes with similar water permeability, the lower the porosity at the outer surface, the more serious the membrane fouling. Furthermore, the effect of the membrane morphology on backwashing performance was discussed.     

Effects of surface heterogeneity on flow circulation in electroosmotic flow in microchannels

The characteristics of electroosmotic flow in a cylindrical microchannel with non-uniform zeta potential distribution are investigated in this paper. Two-dimensional full Navier–Stokes equation is used to model the flow field and the pressure field. The numerical results show the distorted electroosmotic velocity profiles and various kinds of flow circulation resulting from the axial variation of the zeta potential. The influences of heterogeneous patterns of zeta potential on the velocity profile, the induced pressure distribution and the volumetric flow rate are discussed in this paper. This work shows that using either heterogeneous patterns of zeta potential or a combination of a heterogeneous zeta potential distribution and an applied pressure difference over the channel can generate local flow circulations and hence provide effective means to improve the mixing between different solutions in microchannels.     

Effect of Complexation on the Zeta Potential of Titanium Dioxide Dispersions

Abstract

The present paper deals with the surface charge properties and the dispersion stability of an aqueous titania suspension. Generally the titania powder surface is negatively charged. The dispersion stability of TiO₂ suspension is governed by the value of zeta potential. The zeta potential was measured as a function of barium acetate and zinc acetate concentrations, at pH 6.0, and the addition of electrolytes caused sharp decrease of surface charge. Ethylenediaminetetraacetic acid (EDTA) was used to chelate the bivalent metal ions, so that the charge of counterions was reduced. The complexation of bivalent counterions favors the increase of the negative zeta potential and the dispersion stability of aqueous TiO₂ suspension.     

Dipolar anions are not preferentially attracted to the oil/water interface

Homogenization of hexadecane in water at pH 9 gives the same surface charge density in the presence of 0.2 mM thiocyanate or acetate anions as in the presence of chloride, indicating that these dipolar anions are not preferentially adsorbed at the oil/water interface. The decrease in the zeta potential of the emulsion droplets as the sodium salts of iodate, thiocyanate, or acetate are added from 0.1 to 10 mM is the same as that when sodium chloride is added, leading to the same conclusion. Increasing the sodium hydroxide concentration from pH 9 to 11.5 has a different effect on the zeta potential, consistent with the specific adsorption of hydroxide ion at the oil/water interface.     

Zeta potentials of PDMS surfaces modified with poly(ethylene glycol) by physisorption

Controlling zeta potential of PDMS surface coated with a layer of PEG is important for electroosmosis and electrophoresis in PDMS made microfluidic chips. Here, zeta potentials of PDMS surfaces modified by simple physisorption of PEG of different concentrations in phosphate buffer solutions, pure water, and PEG solution were reported. Coating PEG on PDMS surfaces was achieved by immersing a PDMS layer into the PEG solution for 10 min and then taking it out and placing it in an oven at 80℃ for 10 h. To avoid damaging the PEG layer on the PDMS surface, an induction current method was employed for zeta potential measurement. Zeta potentials of PEG modified PDMS in electrolyte solutions were measured. The results show that 2.5% PEG can effectively modify PDMS surface with positive zeta potential value in phosphate buffer solutions, pure water and 10% PEG solution. Further increase in PEG solution beyond 5% for surface modification has no obvious effect on zeta potential change.     

Small-scale preparative supercritical fluid chromatography of cyproterone acetate

Summary A method for the micropreparative fractionation of steroid hormones from process solutions was developed. Using a commercial SFC equipment and raw cyproterone acetate (CPA) as a model sample, we showed the value of SFC as a lab scale purification method and also its potential as an environmentally friendly approach to preparative scale chromatography.     

USING ELECTROPHORESIS TO DETERMINE ZETA POTENTIAL OF MICELLES AND CRITICAL MICELLE CONCENTRATION

A heterodyne laser Doppler electrophoresis method for measuring the zeta potential of a surfactant micelle has been developed. Details of the method and results obtained will be presented in this paper. In comparison with the tracer electrophoresis method used in determining the zeta potential of a surfactant micelle, this method is much time saving and less laborious. The zeta potential values of one anionic and three cationic surfactant micelles have been determined by using this method. From the zeta potential versus concentration curve, one can determine the micellar dissociation concentration and the critical mi cellar concentration of a surfactant. The values obtained agree quite well with the surface tension measurement. The surfactant systems were studied in the presence and absence of NaCI. The zeta potential appears to decrease with the increase of NaCI concentration.     

Role of nanoparticle surface charge in surface-enhanced Raman scattering

In this work, the role of nanoparticle surface charge in surface-enhanced Raman scattering (SERS) is examined for the common case of measurements made in colloidal solutions of Ag and Au. Average SERS intensities obtained for several analytes (salicylic acid, pyridine, and 2-naphthalenethiol) on Ag and Au colloids are correlated with the pH and zeta potential (zeta) values of the nanoparticle solutions from which they were recorded. The consequence of the electrostatic interaction between the analyte and the metallic nanoparticle is stressed. The zeta potentials of three commonly used colloidal solutions are reported as a function of pH, and a discussion is given on how these influence SERS intensity. Also examined is the importance of nanoparticle aggregation (and colloidal solution collapse) in determining SERS intensities, and how this varies with the pH of the solution. The results show that SERS enhancement is highest at zeta potential values where the colloidal nanoparticle solutions are most stable and where the electrostatic repulsion between the particles and the analyte molecules is minimized. These results suggest some important criteria for consideration in all SERS measurements and also provide important insights into the problem of predicting SERS activities for different molecular systems.     

低浓度CTAB对血红蛋白与阿昔洛韦间相互作用与性质的影响

The effects of cetyltrimethylammonium bromide （CTAB） on the properties of hemoglobin （Hb） at low CTAB concentration were studied in Hb/acyclovir/CTAB system by the methods of UV-Vis spectrum, fluorescence, zeta potential, conductivity and negative-staining transmission electron microscope （TEM）. With the increase of CTAB concentration, the UV peak intensity at 276 nm, the intrinsic fluorescence, the zeta potential of Hb and the system conductivity were all enhanced. Hb was easily oxidized to oxyHb and hemichrome. In Hb/acyclovir/CTAB system, CTAB made the UV-Vis spectrum, fluorescence, conductivity and conformation of Hb tend to be returned to those of the original Hb but the zeta potential not to do so. The UV absorption peak of Hb-acyclovir complex disappeared and the tight structure of Hb aroused by acyclovir was refolded. When CTAB concentration was higher than 5 × 10 ^5 mol/L, the two absorption peaks at 536 and 576 nm appeared again, and the Hb structure became looser again.     

Zeta potential measurement for air bubbles in protein solutions

Protein adsorption at gas-liquid interfaces is important in a number of processes including foam formation in bioreactors, foam fractionation for protein recovery, and production of protein based food and drinks. The physical properties of the gas-liquid interface will influence foam stability; important properties will include both surface rheological and electrokinetic properties. While surface rheological properties of gas-protein solution interfaces have been reported, there are no published values for electrokinetic properties at such interfaces. In this paper, zeta potential values of gas bubbles in solutions of three proteins, measured using a microelectrophoresis technique, are reported. The three proteins chosen were BSA, beta-casein, and lysozyme; these proteins have all been used previously in protein foaming studies. The effect of protein concentration and ionic strength is considered. For BSA and beta-casein, zeta potential was found to increase with increasing protein concentration and ionic strength. For air bubbles in lysozyme solutions, measured zeta potential was zero. zeta potential values for air bubbles in some binary protein mixtures are also presented.     

Electrophoretic motion of a slightly deformed sphere with a nonuniform zeta potential distribution

Electrophoretic motion is analyzed for a rigid, slightly deformed sphere with a nonuniform zeta potential distribution. Hydrodynamics and electrostatics solutions for the deformed sphere with an arbitrary double-layer thickness are determined by using the domain perturbation method. The surface shape and the zeta potential distribution for the deformed sphere are expressed by using the multipole expansion representation. In terms of monopole, dipole, and quadrupole moments of the surface shape and the zeta potential distribution, explicit expressions are obtained for the translational and rotational electrophoretic mobility tensors. The ensemble average for the mobility of the deformed sphere with a uniform orientation distribution is also derived. The utility of the general mobility expression is demonstrated by studying the electrophoretic motion of axisymmetric and ellipsoidal particles. The translational and rotational mobilities of axisymmetric particles are both affected by the monopole, dipole, and quadrupole moments of the zeta potential. For ellipsoidal particles, however, the dipole moment of the zeta potential does not affect the translational mobility, while the rotational mobility depends only on the dipole moment. The mobility of the deformed sphere with either a thick or a thin double layer is also derived.     

Evaluation of the permeability of modified cellulose acetate propionate membranes for use in biosensors based on hydrogen peroxide detection

Phase inversion cellulose acetate propionate membranes showed lowpermeability to hydrogen peroxide aqueous solutions. Their permeability wasincreased by alkaline hydrolysis of the ester linking units. However, thepermeability remained lower than that of an unsubstituted cellulose membrane.The inclusion of hydroxypropyl cellulose in the membrane formulation, followedby an alkaline hydrolysis step, increased permeability to hydrogen peroxideaqueous solutions to 29% of that of an unsubstituted cellulose membrane.     

Facile Hydrolysis and Alcoholysis of Palladium Acetate

Palladium(II) acetate is readily converted into [Pd₃(μ²‐OH)(OAc)₅] ( 1 ) in the presence of water in a range of organic solvents and is also slowly converted in the solid state. Complex 1 can also be formed in nominally anhydrous solvents. Similarly, the analogous alkoxide complexes [Pd₃(μ²‐OR)(OAc)₅] ( 3 ) are easily formed in solutions of palladium(II) acetate containing a range of alcohols. An examination of a representative Wacker‐type oxidation shows that the Pd‐OH complex 1 and a related Pd‐oxo complex 4 can be excluded as potential catalytic intermediates in the absence of exogenous water.     

Numerical study of electroosmotic slip flow of fractional Oldroyd-B fluids at high zeta potentials

In this paper, an investigation of the electroosmotic flow of fractional Oldroyd-B fluids in a narrow circular tube with high zeta potential is presented. The Navier linear slip law at the walls is considered. The potential field is applied along the walls described by the nonlinear Poisson–Boltzmann equation. It's worth noting here that the linear Debye–Hückel approximation can't be used at the condition of high zeta potential and the exact solution of potential in cylindrical coordinates can't be obtained. Therefore, the Matlab bvp4c solver method and the finite difference method are employed to numerically solve the nonlinear Poisson–Boltzmann equation and the governing equations of the velocity distribution, respectively. To verify the validity of our numerical approach, a comparison has been made with the previous work in the case of low zeta potential and the excellent agreement between the solutions is clear. Then, in view of the obtained numerical solution for the velocity distribution, the numerical solutions of the flow rate and the shear stress are derived. Furthermore, based on numerical analysis, the influence of pertinent parameters on the potential distribution and the generation of flow is presented graphically.     

Flow through Porous Media XVI: Electrokinetic Transport Coefficients of Aqueous Solutions of Mercuric Chloride and Glycine through a Sintered Disc Impregnated with a Cellulose Acetate Membrane under a Magnetic Field

The effect of the magnetic field on the electrokinetic transport coefficients (permeability coefficient and electro-osmotic permeability coefficient) of water and aqueous solutions of mercuric chloride and glycine through a sintered disc impregnated with cellulose acetate at different potentials, concentrations, and magnetic fields varying up to 21 kg/cm² are reported at 308.15 K. The phenomenological coefficients characterizing the electro-osmotic flow and the membrane characteristics are also estimated for the various solutions with the object of determining the efficiencies of electrokinetic energy conversion and ζ potential. The effect of magnetic field has been attributed to the molecular orientation of dipoles in solutions and to the change in the structure of the membrane.     

Mathematical Methods in the Calculation of the Zeta Potential of BSA

This article is focused on the zeta potential of bovine serum albumin (BSA). It is useful to know the zeta potentials of substances for further use of them, e.g. for adsorption or the stability of prepared solutions. We decided to create a database of zeta potential measurement. BSA was selected as a model protein for the measurements. The zeta potential was measured at different pH values, temperatures, concentrations and in the presence of KCl and \(\hbox {CaCl}_{2}\). All data were collected and used for the creation of the online application. The users of the online application can select an interval of zeta potentials required and the application shows the conditions under which the BSA solutions should be prepared. These measurements can be used to save time for further experiments, where the database can be used for the direct preparation of samples with desired properties instead of the lengthy preparation of the samples under different conditions and the selection of the appropriate parameters.     

Modeling electroosmotic and pressure-driven flows in porous microfluidic devices: zeta potential and porosity changes near the channel walls

This work presents analytical solutions for both pressure-driven and electroosmotic flows in microchannels incorporating porous media. Solutions are based on a volume-averaged flow model using a scaling of the Navier-Stokes equations for fluid flow. The general model allows analysis of fluid flow in channels with porous regions bordering open regions and includes viscous forces, permitting consideration of porosity and zeta potential variations near channel walls. To obtain analytical solutions problems are constrained to the linearized Poisson-Boltzmann equation and a variation of Brinkman's equation [Appl. Sci. Res., Sect. A 1, 27 (1947); 1, 81 (1947)]. Cases include one continuous porous medium, two adjacent regions of different porosities, or one open channel adjacent to a porous region, and the porous material may have a different zeta potential than that of the channel walls. Solutions are described for two geometries, including flow between two parallel plates or in a cylinder. The model illustrates the relative importance of porosity and zeta potential in different regions of each channel.     

Effect of low-molecular-weight organic anions on electrokinetic properties of variable charge soils

It is known that some inorganic anions can be adsorbed by variable-charge soils specifically, resulting in the lowering of the zeta potential of the clay particle. Reasoning similarly, organic anions should also have such an effect. In this article, the effect of the anions of five low-molecular-weight (LMW) organic acids existing widely in soils on the zeta potentials of two variable-charge soils was examined. The results showed that the presence of organic anions led to a decrease in zeta potential. The effect of different anions on zeta potential followed the order oxalate>citrate>malate>maleate>acetate. The effect increased with the increase in anion concentration and decreased with the increase in pH. The extent of the effect on different soils was apparently related to their iron oxide content. The presence of organic anions also led to a decrease in the isoelectric point (IEP) of the soil. The IEPs of two soils in organic anion systems followed the order acetate>maleate>malate>citrate. No IEP was detected for the oxalate system.     

Determining the Zeta Potential of Porous Membranes Using Electrolyte Conductivity inside Pores

The zeta potential is an important and reliable indicator of the surface charge of membranes, and knowledge of it is essential for the design and operation of membrane processes. The zeta potential cannot be measured directly, but must be deduced from experiments by means of a model. The possibility of determining the zeta potential of porous membranes from measurements of the electrolyte conductivity inside pores (lambda(pore)) is investigated in the case of a ceramic microfiltration membrane. To this end, experimental measurements of the electrical resistance in pores are performed with the membrane filled with KCl solutions of various pHs and concentrations. lambda(pore) is deduced from these experiments. The farther the pH is from the isoelectric point and/or the lower the salt concentration is, the higher the ratio of the electrolyte conductivity inside pores to the bulk conductivity is, due to a more important contribution of the surface conduction. Zeta potentials are calculated from lambda(pore) values by means of a space charge model and compared to those calculated from streaming potential measurements. It is found that the isoelectric points are very close and that zeta potential values for both methods are in quite good agreement. The differences observed in zeta potentials could be due to the fact that the space charge model does not consider the surface conductivity in the inner part of the double layer. Measurements of the electrolyte conductivity within the membrane pores are proved to be a well-adapted procedure for the determination of the zeta potential in situations where the contribution of the surface conduction is significant, i.e., for small and charged pores. Copyright 2001 Academic Press.