Impact of contaminated nanoparticles on the non-monotonous change in the concentration of mobile ions in liquid crystals

The ionic purity of nanoparticles can affect electrical properties of liquid crystals in very unusual ways. While 100% pure nanoparticles can only decrease the concentration of mobile ions in liquid crystals by means of adsorption/desorption processes, nano-dopants contaminated with ions can lead to the increase, decrease and no change in the concentration of ions. Moreover, these changes can exhibit non-monotonous behaviour as a function of the nanoparticle loading. The level of the liquid crystal contamination or purification, achieved by doping them with nanoparticles, is always limited by the physical quantity called the critical concentration of ions. From applied perspectives, results presented in this paper can be used in the selection of nano-materials, the most suitable for the liquid crystal purification.     

Composite polarizability and the construction of an invariant function of refraction and mass density for solutions

Re-examination of dynamical ionic polarizabilities in water solutions leads to the formulation of a solution function r(c), which combines the indices of refraction and mass densities of solutions. We show that this function should be independent of ionic concentration if the composite polarizabilities of hydrated solute clusters are constant. Using existing experimental data for a number of aqueous salt and organic solutions, we find that the r(c) function is either constant or varies linearly with concentration, in most cases with negligible slope. We use this function to compare ionic polarizabilities of crystals and aqueous solutions and to highlight how solute polarizabilities at infinite dilution scale with the electronic valence shell of cations and anions. The proposed r(c) function can be used generally to verify the consistency of experimental measurements and of simulation results, and it provides a test of assumptions in current theories of ionic polarizabilities.     

Standard systems for measurement of pK values and ionic mobilities: 2. Univalent weak bases

This paper contributes to the methodology of measuring pK values and ionic mobilities by capillary zone electrophoresis by introducing the principle of constant ionic strength and minimum interaction of analytes with counterionic components and presenting a standard system of cationic buffers for measurements of weak bases. The system is designed so that all buffers comprise the same concentration of Cl⁻ present as the only counter anion. This minimizes problems caused by interactions between the counterion and the analytes which may otherwise bring biased values of obtained effective mobilities. Further, the buffer system provides constant and accurately known ionic strength for an entire set of measurements. When additionally all measurements are performed with constant Joule heating, one correction for ionic strength and temperature is then needed for the obtained set of experimental data. This considerably facilitates their evaluation and regression analysis as the corrections for ionic strength and Joule heating need not be implemented in the computation software and may be applied only once to the final regression results. An experimental example of the proposed methodology is presented and the reliability and the advantages of the proposed system are shown, where the known problematic groups of amines and pyridine were measured with high accuracy and without any notice of anomalous behavior.     

流体力学半径对估算胶体微球聚集速率常数的影响

胶体粒子聚集速率常数实验值远低于理论值一直是被普遍关注的问题.聚集速率常数的理论推导是基于粒子的几何半径来考虑的,但决定粒子扩散速率及聚集速率的应该是粒子的流体力学半径(大于几何半径),因而它是使聚集速率常数实验值低于理论值的因素之一.影响流体力学半径的因素很多,其中,带电粒子在溶液中因表面存在双电层,会明显增大流体力学半径,造成聚集速率减慢.而双电层的厚度又随溶液中离子强度的不同而改变.本工作在聚集速率的公式中引入了修正因子,即几何半径与其流体力学半径之比,以修正由于用几何半径代替流体力学半径带来的误差.其中几何半径和流体力学半径可以分别用扫描电镜(SEM)和动态光散射(DLS)来测定.以两种粒径的聚苯乙烯带电微球为例,考察了在不同离子强度下,该误差的大小.结果发现,对于半径为30 nm的微球,用流体力学半径计算的慢聚集速率常数比理论值偏低约8%.该误差随离子强度增加而减少.对于快聚集情况,流体力学半径对聚集速率基本没有影响.     

Determination of thermodynamic acidity constants and limiting ionic mobilities of weak electrolytes by capillary electrophoresis using a new free software AnglerFish

Thermodynamic acidity constants (acid or acid-base dissociation constants, sometimes called also as ionization constants) and limiting ionic mobilities (both of them at defined temperature, usually 25°C) are the fundamental physicochemical characteristics of a weak electrolyte, that is, weak acid or weak base or ampholyte. We introduce a novel method for determining the data of a weak electrolyte by the nonlinear regression of effective electrophoretic mobility versus buffer composition dependence when measured in a set of BGEs with various pH. To correct the experimental data for zero ionic strength we use the extended Debye-Hückel model and Onsager-Fuoss law with no simplifications. Contrary to contemporary approaches, the nonlinear regression is performed on limiting mobility data calculated by PeakMaster's correction engine, not on the raw experimental mobility data. Therefore, there is no requirement to perform all measurements at a constant ionic strength of the set of BGEs. We devised the computer program AnglerFish that performs the necessary calculations in a user-friendly fashion. All thermodynamic pKa values and limiting electrophoretic mobilities for arbitrarily charged substances having any number of ionic forms are calculated by one fit. The user input consists of the buffer composition of the set of BGEs and experimentally measured effective mobilities of the inspected weak electrolyte.     

Polycondensation kinetics of orthosilicic acid in a hydrothermal solution

The polycondensation kinetics of orthosilicic acid in hydrothermal solutions was studied experimentally at different temperatures, pH, and ionic strengths. As a result of the mathematical processing of experimental data, equations approximating the time dependence of the polycondensation process and the dependence of the polycondensation rate constant on the solution ionic strength were obtained. Experimental data on the kinetics of the reverse process of dissolving colloidal silica were obtained at different temperatures and pH.     

Time-dependent electrical properties of liquid crystal cells: unravelling the origin of ion generation

An understanding of possible sources of ion generation in liquid crystal materials is of utmost importance to ensure uncompromised performance of modern liquid crystal devices. In this paper, time-dependent electrical properties of filled liquid crystal cells are used to reveal important information about often overlooked source of ion generation in liquid crystals. This source of ions originates from the ionic contamination of substrates of the liquid crystal cell. Ionic contaminants can be inherently present in the alignment layers or can be induced by external factors such as mechanical rubbing or irradiation with light. The model of this ion generation process is presented and tested using existing experimental data.     

Micelle–monomer equilibria in solutions of ionic surfactants and in ionic–nonionic mixtures: A generalized phase separation model

On the basis of a detailed physicochemical model, a complete system of equations is formulated that describes the equilibrium between micelles and monomers in solutions of ionic surfactants and their mixtures with nonionic surfactants. The equations of the system express mass balances, chemical and mechanical equilibria. Each nonionic surfactant is characterized by a single thermodynamic parameter — its micellization constant. Each ionic surfactant is characterized by three parameters, including the Stern constant that quantifies the counterion binding. In the case of mixed micelles, each pair of surfactants is characterized with an interaction parameter, β, in terms of the regular solution theory. The comparison of the model with experimental data for surfactant binary mixtures shows that β is constant — independent of the micelle composition and electrolyte concentration. The solution of the system of equations gives the concentrations of all monomeric species, the micelle composition, ionization degree, surface potential and mean area per head group. Upon additional assumptions for the micelle shape, the mean aggregation number can be also estimated. The model gives quantitative theoretical interpretation of the dependence of the critical micellization concentration (CMC) of ionic surfactants on the ionic strength; of the CMC of mixed surfactant solutions, and of the electrolytic conductivity of micellar solutions. It turns out, that in the absence of added salt the conductivity is completely dominated by the contribution of the small ions: monomers and counterions. The theoretical predictions are in good agreement with experimental data.     

ATP与Mg2+、Ca2+生成配合物反应的热力学研究

The formation constant (K) and thermodynamic parameters (ΔC.ΔH.ΔS) in reactions in which complexes of adenosine triphosphate with magnesium ion and calcium ion are formed have been obtained by a microcalorimetric method. All experimentes were made at 30 ℃, pH=8.0 and at ionic strength μ=0.2 mol L~(-1). Measured experimental values indicate that complex formation reactions are driven by the entropic factor.     

Reliable measurements of interfacial slip by colloid probe atomic force microscopy. I. Mathematical modeling

We developed a stable spread-sheet algorithm for the calculation of the hydrodynamic forces measured by colloid probe atomic force microscopy to be used in investigations of interfacial slip. The algorithm quantifies the effect on the slip hydrodynamic force for factors commonly encountered in experimental measurements such as nanoparticle contamination, nonconstant drag force due to cantilever bending that varies with different cantilevers, flattening of the microsphere, and calibration at large separations. We found that all of these experimental factors significantly affect the fitted slip length, approximately in the order listed. Our modeling is applied to fit new experimental data reproducibly. Using this new algorithm, it is shown that the fitting of hydrodynamic theories to experimental data is reliable and the fitted slip length is accurate. A "blind test" protocol was developed that produces a reliable estimate of the fitting error in the determination of both the slip length and spring constant. By this blind test, we estimate that our modeling determines the fitted slip length with an average systematic error of 2 nm and the fitted spring constant with a 3% error. Our exact calculation of the drag force may explain previous reports that the fitted slip length depends upon the shape and spring constant of the cantilever used to perform the measurements.     

An orthogonal design of experiment/exploratory data analysis for plutonium contamination

This paper describes a statistical-experimental design approach for identifying sources of Pu contamination in the radioactivity material analysis of dried shellfish at the National Institute of Standards and Technology (NIST). Identification and elimination of sources of contamination were required for certifications of the radioactivity concentration of actinides in the proposed reference material. Sources of contamination included the fume hood, glassware, and reagents. The experimental design employed reduced number of required experiments by a factor of 100. The result is an orthogonal design of experiment (ODEX) and subsequent data was analyzed using Exploratory Date Analysis (EDA), which narrowed the 200+ experiments to a manageable 16. This design made it possible to identify the sources and interactions of sources of contamination in a timely and cost effective manner.     

Measurements of calcium with a fluorescent probe Rhod-5N: Influence of high ionic strength and pH

We describe a new method for the spectroscopic determination of high calcium concentration using a fluorescent probe Rhod-5N. This method was investigated in order to be utilized in high ionic strength solution, such as seawater. The probe is fluorescent when bound to calcium, LM, but not as the free form L. The dissociation constant of the equilibrium (0.14 mM) was determined at several ionic strengths, i.e. in the absence and in the presence of additional ions (0.7 M NaCl). The influence of pH was studied. In order to correctly model the experimental data, we included a new fluorescent compound: LHM (calcium bound protonated probe). The first acidity constant (0.02 μM) and the second dissociation constant (4.5 mM) were calculated. A useful range for the determination of calcium concentration is provided. Such a method is fast and easy to carry out.     

Mean Ionic Activity Coefficients of Alkali Metals Dissolved in High Dielectric Constant Solvents: A Comparison Between Experimental Data and Fuoss Theoretical Data

Abstract

Ionic association of strong univalent symmetrical electrolytes dissolved in Hydrogen Bonded Solvents (HBS) having high dielectric constants, has been studied in terms of mean ionic activity coefficient. This parameter has been analysed with the Fuoss's Paired Ion Model in the concentration range 0.5-500m0lm^-3. The experimental data are consistent with this model. It has been shown that fits to the experimental data could be obtained with fixed values of fraction of contact pain α and Gurney radius corresponding to the Contact Pair (CP). The results of fractions of free ions γ and conducting ions (p) as a function of concentration are also discussed. Conductimetric pairing constants K Lanbad; and Gibbs free energy δG are deduced to explain this ionic association. The iduence of the dielectric constant of the solvent on the ionic association has been also investigated in this work.     

醚基功能化离子液体[MOEMIm]Cl和[EOEMIm]Cl热力学性质

通过核磁共振氢谱,核磁共振碳谱,元素分析和热重分析对醚基功能化的离子液体[MOEMIm]Cl和[EOEMIm]Cl进行了表征。在温度范围T=288.15–328.15 K内,测定了离子液体[MOEMIm]Cl和[EOEMIm]Cl的密度(ρ)、表面张力(γ)和折光率(nD)。根据这些实验数据,讨论并计算了离子液体[MOEMIm]Cl和[EOEMIm]Cl的体积性质。计算出离子液体[MOEMIm]Cl和[EOEMIm]Cl的摩尔表面吉布斯自由能(gs)、摩尔表面熵(s)、摩尔表面焓(h)、摩尔极化度(Rm)和摩尔极化率(αp),h均近似为一个常数说明这两种离子液体从内部到表面的过程是一个等库仑过程,同时这两种离子液体的Rm和αp均与温度无关。本文还用摩尔表面Gibbs自由能改进Lorentz-Lorenz方程并预测离子液体表面张力,预测值与实验值高度相关。     

Effect of simple electrolytes on the hydrodynamic radius of polystyrene latex

We studied the salt concentration dependence of the diffusion constant of the highly charged and monodispersed polystyrene latex sphere using the techniques of dynamic light scattering. At extremely low ionic strength, the diffusion constant is smaller than that at the higher ionic strength by 10 % of the latter value. The addition of smal amount of N(CH₃) ₄ ⁺ to the latex solution increases the diffusion constant. These experimental results are explained by the change of the hydrodynamic radius which depends on sizes of the polystyrene core and the structural water surrounding it.     

NaCl-KCl-H2O体系的体积性质及其与Pitzer模型的相关性研究

本文用高精度数字式振荡管密度计测定了288K至323K温度范围内NaCl?KCl混合溶液的密度,溶液的离子强度范围从0.1到4 mol.kg_^–1。用密度实验值计算了三元体系的超额体积并拟合得到了实验温度和浓度范围内的Pitzer模型参数,模型计算值与实验值的偏差在±0.0004 g.cm_^–3以内。用Pitzer模型计算了不同离子强度下三元体系在298.15K下的混合体积。     

Citric acid oxidation by vanadium(V) in sulfuric acid medium: Kinetic and mechanistic study

The citric acid oxidation by vanadium(V) in sulfuric acid medium at 303 K is reported. The reaction rate was determined spectrophotometrically by monitoring the formation of vanadium(IV) at 760 nm. The oxidation showed a first‐order dependence with respect to vanadium(V) concentration and fractional order with respect to citric acid concentrations, with no control and with constant ionic strength. The reaction is also first order with respect to sulfuric acid concentration with no control and of fractional order at constant ionic strength. The reaction rate is enhanced by an increase of ionic strength and increased by a decrease of the dielectric constant. The activation parameters were calculated based on the rate constants determined in the 293 to 313 K interval. The proposed oxidation mechanisms and the derived rate laws are consistent with the experimental rate laws. © 2000 John Wiley & Sons, Inc. Int J Chem Kinet 32: 566–572, 2000     

Speciation of the uranyl nitrate system via spectrophotometric titrations

The speciation of the uranyl nitrate system has been studied previously with limited success producing a wide range of stability constant values. The current literature has values for the mononitrate species, with scattered data for higher nitrate species. Furthermore, the reported values vary with experimental method. The work presented here examines the stability of the uranyl/nitrate/perchlorate/water system via spectrophotometric titrations with a focus on the predominance of the uranyl dinitrate species at low nitrate concentrations. Stability constants were determined at ionic strengths ranging from 1 to 6 molal followed by refinement with the specific ion interaction theory. The zero ionic strength stability constant of the uranyl dinitrate species was refined as log β (2,1)º = 3.37 ± 0.02 when including the stability constant for the uranyl mononitrate from Ahrland and 2.66 ± 0.02 without. These values are considerably higher than previous studies, which is attributed to the alternate speciation model used. The values generated in this work produce speciation diagrams that are consistent with published solvent extraction data of the uranyl nitrate system.     

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.