Electrokinetic flow velocity in charged slit-like microfluidic channels with linearized Poisson-Boltzmann field

In cases of the microfluidic channel, where the thickness of electric double layer is often comparable with the characteristic size of flow channels, the electrokinetic influence on the flow behavior can be found. The externally applied body force originating from the electrostatic interaction between the linearized Poisson-Boltzmann field and the flow-induced electrical field is applied in the equation of motion. An analytical solution to this Navier-Stokes equation of motion for well-defined geometry of slit-like microchannel is obtained by employing Green’s function. Also, an explicit analytical expression for the induced electrokinetic potential is successfully derived as functions of relevant physicochemical parameters. The effects of the ionic concentration of the fluid, the zeta potential of the solid surface, and the width of microchannels on the velocity profile as well as the streaming potential are examined. The electric double layer effect on the velocity profile becomes stronger as the channel width decreases, where the average fluid velocity is entirely reduced with the decrease in ionic concentration. The induced electrokinetic potential increases with an increase in pressure gradient, while it decreases as the ionic concentration increases.     

Electrophoresis in concentrated dispersions of charged porous spheres

Electrophoresis in a concentrated suspension of charged porous spheres is investigated theoretically, taking into account of the polarization effect of double layer in particular. The double layer thickness and fixed charge density of the porous spheres are arbitrary and double layer overlapping is considered as well. A pseudo-spectral method based on Chebyshev polynomial is used to solve the resulted general electrokinetic equations. Local extrema are observed in the mobility profile as the double layer thickness varies, which is absent in previous theoretical studies neglecting polarization effect but agrees well with the experimental observations in the literature, indicating the importance of polarization effect in correctly interpreting the electrophoretic experimental results. A simple mutual transform of mobility predictions between Levine-Neale and Shilov-Zharkikh boundary conditions is established and confirmed by direct calculations, which facilitates the dialogue between theoretical and experimental researches. In general, the higher the fixed charge density, the more significant the polarization effect is.     

Electrokinetic properties of textile fabrics

This paper reports electrokinetic phenomena concerning the properties of textile fabrics that are crucial for dyeing and finishing processes. These interface phenomena influence the adsorption of surfactants, optical brighteners, dyes and finishing agents due to interaction forces between the fibre surface and solution. Zeta potential, isoelectric point, point of zero charge and the amount of surface charge of standard adjacent fabrics (cotton, wool, viscose rayon, polyamide, polyester and acrylic) have been determined. Electrokinetic potential was measured by a method involving streaming potential/current using an electrokinetic analyser. The specific amount of surface charge was calculated by a back-titration method.     

选煤废水（CPW）混凝过程中Ca2＋作用特性研究

用硫酸钙和硫酸铝作凝聚剂、PAM作絮凝剂对同一选煤废水（CPW）做混凝试验,测定电动电位和澄清水的SS。通过试验数据和试验现象的分析认为Ca2＋和Al3＋的作用机理不同。Ca2＋是和煤粒表面通过化学键发生化学吸附,即在双电层内产生定位离子吸附,既改变了煤粒的表面电位,又改变了电动电位。考电位随cah浓度的增大而降低,但降幅不大。Ca2＋被沉淀物带走的较少,澄清水中含有大量可循环利用的Ca2＋。必须保证废水体系中Ca2＋浓度足够高才能使Ca2＋具有足够强的与其他离子（如Al3＋、H＋、Na＋、K＋）的竞争性。Ca2＋能降低PAM的利用效率。     

血红蛋白-银的反应及凝胶性能的研究

分别用UV－Vis、电导、电泳等方法研究了血红蛋白同银离子间的相互作用。考察了介质的pH、温度、浓度等条件对血红蛋白同银离子作用的影响；血红蛋白－银凝胶体系在211．6和436．6nm处有最大吸收；银氨配离子在碱性条件下还原为银粒而被血红蛋白吸附形成超细银凝胶。胶体带正电荷，双电层的电动电位为0．093－0．118V。     

无机电解质对有机染料水分散体稳定性及动电性质影响研究

本文制备了不同浓度的阴离子表面活性剂或非离子表面活性剂—分散染料(C.I.分散蓝79)水分散体系,并以沉降度作为分散体的稳定参量,动电位为颗粒电结构参量,研究了无机电解质对这些分散体的稳定性和动电性质的影响。动电性质实验和沉降实验良好符合。结果表明,较低浓度的无机电解质能辅助扩散双电层的建立从而增加分散体稳定性;当其浓度超过某临界值时又会压缩双电层从而成为不稳定因素。尽管电解质浓度增大使表面活性剂在染料颗粒表面吸附量增大,但电解质对双电层的直接影响始终占主导地位。     

Electrochemical and electrokinetic characterization of cellulose acetate polymeric membranes

The electrochemical and electrokinetic aspects of cellulose acetate membranes of varying pore structure and desalting abilities have been investigated. The electrochemical studies included measurement of conductance and membrane potential for various membrane electrolyte systems. The electrokinetic characterization was made from streaming potential measurements. The data obtained are explained in terms of interfacial double layer phenomena prevalent in porous permselective barrier systems. The average pore diameter evaluated independently is also presented and an attempt has been made to understand the solute–water transport in terms of weak ionic character of membrane surface.     

C-S-H/solution interface: Experimental and Monte Carlo studies

The surface charge density of C-S-H particles appears to be one of the key parameters for predicting the cohesion strength, understanding the ion retention, the pollutant leakage, and admixture adsorption in hydrated cement pastes.This paper presents a Monte Carlo simulation of the surface-ions interactions that permits the prediction of surface charge density (σ), electrokinetic potential (ζ) and ions adsorption of mineral surfaces in equilibrium with a given electrolyte solution. Simulated results are compared to experimental data obtained by titration, electrokinetic potential measurements and ions uptake in the case of C-S-H suspensions. An excellent agreement is found between simulated and experimental results.The wide spread idea that calcium is a potential determining ion in cement paste systems appears to be incorrect. Instead, the pH controls the charging behaviour of C-S-H nano-particles. This paper also shows to what extent the electrostatic interactions contribute to the measured Ca/Si ratio.     

MECHANICALLY INDUCED STIMULATION OF ELECTROMAGNETIC RADIATION—A NEW ELECTROKINETIC PHENOMENON

It is shown that there must be six. not just four electrokinetic phenomena involving the ionic double layers on solids making contact with liquids. In one of these, the emission of electromagnetic waves from mechanically stimulated colloid systems should be observable. This prediction is based upon the fact that suspended particles in polar liquids normally bear an ionic double layer of charge. The outer liquid-borne portion is readily distortable. Cyclic distortion of it will produce a radiating dipole. Preliminary experimental results show silica gel and yeast (Saccharomyces cerevisiae) suspensions to produce such electromagnetic radiation. The electromagnetic noise in the natural motions of sea and fresh waters may be due in part to this phenomenon.     

临阈浓度时纳滤膜软化过程中膜面动电现象研究

荷电纳滤（NF）膜在相似浓度范围的进水端主体溶液软化过程中,浓水端的膜面处易出现结垢污染,因此开展临阈浓度条件下膜表面动电现象研究是十分必要的。本文选定DK型NF膜和c_K2SO4：c_CaCl2=1：1的双组分溶液为载体,以CaSO₄·0.5H₂O为典型代表的非碱性难溶垢为研究对象,通过自制的切向流动电位测试系统,分别考察临阈浓度条件下,进水端主体溶液中不同构晶离子浓度（0.5～18 mol·m^-3）、操作压力（25～200 kPa）和不同pH（3.0～10.0）对该NF膜流动电位、Zeta电位和膜表面电荷密度的影响效应。当操作压力恒定为180 kPa且逐渐增加构晶离子浓度（0.5～18 mol·m^-3）时,DK膜面流动电位和Zeta电位绝对值分别从87.37和59.13 mV下降至3.41和36.34 mV,均呈先急剧后缓慢下降的变化趋势。这可能是由于静电屏蔽和扩散层压缩共同作用的结果。而同时膜面电荷密度从13.94 mC·m^-2逐渐增加至34.86 mC·m^-2。研究表明,当NF浓水端膜面处开始出现结垢时,膜表面仍有中低强度的动电现象。     

Electrical double layer in solid electrolytes—theory: oxide electrolytes

The surface structure model of ionic crystal and the equivalent circuit of electrical double layer on the interface of solid electrolyte/vacuum or solid electrolyte/blocking electrode is suggested, taking into account intrinsic disorder of surface layer. In terms of this model the expressions are obtained for surface capacity as a function of potential, temperature and defect concentrations in solid electrolyte.In oxide solid electrolytes from ZrO₂ doped by Y₂O₃, CaO, Yb₂O₃ on the liquid metal droplet (Ag, Sn and CuSn, AuSn, AuCu alloys) near parabolic dependence of double layer capacitance on potential has been established. The minimum capacitance increases exponentially with temperature and decreases in inverse proportion to charge carrier concentration. The minimum capacitance potential coincides within error limits with zero charge potential, which does not depend on temperature; its position is determined by the electrode nature and does not depend on the electrolyte composition. All of these peculiarities agree well with the theoretical conclusions.     

Influence of Solids Concentration on the Isoelectric Point of Aqueous Barium Titanate

We report on findings that the particle surface charge is influenced by solids concentration in aqueous suspensions of BaTiO₃. Three decades in solids concentration were analyzed by combining results from two different electrokinetic methods. Combined results demonstrate a systematic acidic shift in the isoelectric pH with decreasing solids concentration. The shift is attributed to the development of a Ba-depleted, TiO₂-rich surface layer. Using kinetic arguments, it is shown that the thickness of this layer will be proportional to the surface-to-volume ratio.     

Influence of Surfactants on the Rate of Decomposition of Apatites by Mineral Acids

The dependence of the true rate of decomposition of fluorapatite and hydroxylapatite in nitric, sulfuric, and orthophosphoric acids on the concentration of a surfactant (cetylpyridinium chloride and sodium dodecyl sulfate) was experimentally studied. The electrokinetic potential in the slip plane of the double electric layer at the interface between apatite and an aqueous solution of a surfactant was measured by the electroosmotic method. The concentrations of cetylpyridinium chloride (5.5 × 10^–6 mol/l) for fluorapatite and sodium dodecyl sulfate (1 × 10^–4 mol/l) for hydroxylapatite were found, which correspond to the isoelectric state of the surface of the solid phase. It was established that the true rate of decomposition of apatites is maximal when the electrokinetic potential is zero.     

Possible Electrical Double-Layer Contribution to the Equilibrium Thickness of Intergranular Glass Films in Polycrystalline Ceramics

The plausibility of the entropic repulsion of electrical double layers acting to stabilize an equilibrium thickness of intergranular glass films in polycrystalline ceramics is explored. Estimates of the screening length, surface potential, and surface charge required to provide a repulsive force sufficiently large to balance the attractive van der Waals and capillary forces for observable thicknesses of intergranular film are calculated and do not appear to be beyond possibility. However, it has yet to be established whether crystalline particles in a liquid-phase sintering medium possess an electrical double layer at high temperatures. If they do, such a surface charge layer may well have important consequences not only for liquid-phase sintering but also for high-frequency electrical properties and microwave sintering of ceramics containing a liquid phase.     

Interaction Free Energy Studies on Floe Foam Flotation

Abstract

The Gouy-Chapman theory of the electric double layer is applied to the calculation of interaction free energy of a charged surface film and a solid surface of opposite charge immersed in a solution of electrolyte. The interaction energies calculated with a constant surface charge density model and a constant surface potential model are compared. A constant surface charge density model for floe foam flotation is found to result in less effective binding energy than the constant surface potential model. The constant surface potential model can be found to account for the decrease in efficiency of floe foam flotation which is observed experimentally when ionic strength is increased. However, studying the binding energy at various ionic strengths with the constant surface charge density model gives results that are contradictory to the experimental results. We can thus conclude that the floe foam flotation system is better analyzed with a constant surface potential model.     

Surface Characteristics of Kaolinite and Other Selected Two Layer Silicate Minerals

The electrokinetic features and interfacial water structure, as revealed from molecular dynamics simulations (MDS) are considered with respect to the anisotropic features of selected two layer silicate minerals. Planar structures of kaolinite and antigorite are compared to the, compositionally equivalent, tubular structures of halloysite and chrysotile with respect to the pH dependency of zeta potential as determined from the electrophoretic mobility measurements. The importance of the atomic mismatch between the tetrahedral and octahedral sheets in a particular bilayer is discussed in order to explain the electrokinetic behaviour of these two layer silicate minerals. Interfacial water structure from MDS suggests that the silica tetrahedral surface is not wetted by water. In the case of planar silicates structural imperfections are considered to explain wetting characteristics. The possibility of polarity reversal (domain inversion) within a tetrahedral/octahedral layer and an out‐of‐order layer (inserted layer) within the tetrahedral/octahedral stack are considered in order to explain electrokinetic behaviour and wetting characteristics.     

Interfacial properties of polyelectrolyte–cellulose systems. II. Electrokinetic properties of cellulose fibers with adsorbed monolayers of cationic polyelectrolyte

Zeta potential measurements by the streaming current method were performed on pulp (DP) fibers with or without irreversibly adsorbed monolayers of cationic polyelectrolyte. Factors affecting the electrokinetic properties of these fibers, such as the amount of adsorbed polymer, the polymer molecular weight (M_n 50,000 and 200,000), ionic strength (10^?5 ～ 10^?2M KCl), and the pH of the streaming medium (KCl solution), were examined. As the amount of adsorbed polymer increased, the negative zeta potential of the fibers decreased until the polarity of the zeta potential was reversed to the positive side. A marked change in the value of zeta potential was not observed when the formation of the saturated monolayer was completed. The zeta potential also varied in proportion to an increase in the amount of polymer adsorbed. Experimental results are interpreted with reference to the origin of the surface charge, the amphoteric nature of the surface, the modes of adsorption, and the adsorbed polymer chain configuration. Possible effects of the adsorbed monolayer formation on the structural change of the electric double layer at the fiber surface are discussed. It is concluded that the formation of a monolayer of cationic polyelectrolytes on the negatively charged cellulose fibers under the condition of k₁ > k₂ (part I) provides a means to arbitrarily control the charge of the fibers until formation of a saturated monolayer.     

Dielectric spectroscopic characterization of a weak-acid polystyrene colloid

A commercially available aqueous polystyrene colloid with surface -COOH groups was purified by exhaustive dialysis. This was then investigated for dielectric frequency response in the low frequency domain (0.01-100 Hz), as a function of pH, ionic strength and the chemical nature of the counterions in the electrical double layer. In previous work on strong-acid (sulfonate) colloids it had been shown that a plot of the imaginary part of the complex impedance as a function of the real part gave semicircles whose radii were a direct function of the surface charge density. In this work, surface charge is a function of pH. The degree of counterion binding was a function of hydrated ion size, as determined from an analysis of titration data and ionic strength of the continuous phase, which in turn was determined from the phase angle and the characteristic relaxation frequency. Dielectric spectroscopy is thus a powerful non-invasive tool for quantitative analysis of the properties of the electrical double layer in these systems.     

Electro-kinetically enhanced mass transport of charged macro-solutes through a microchannel with porous walls

Electrokinetics of the solute transport across the porous walls of micro channel is important from its practical application but less explored. Transport of the charged macro-solutes across perm-selective walls in a microchannel is investigated. The extended Nernst–Planck equation describes the charged macro-solutes distribution in the mass transfer boundary layer over the porous wall. The transverse electromigration of the charged macro-solute either augments or suppresses the concentration polarization and the permeation rate depending on the wall and solute surface potential (attractive or repelling). The wall potential is screened due to the electrical double layer interaction of the wall and charged solute. It is observed that the charged solute concentration over the channel wall enhances by two times in case of oppositely charged interactions (unlike solute and channel wall) compared to like charges. The findings of this study can facilitate understanding of electrokinetic based drug delivery and separation systems involving charged solutes.