Theory of Frequency-Dependent Polarization of General Planar Electrodes with Zeta Potentials of Arbitrary Magnitude in Ionic Media

Electrode polarization effects have long aggravated the efforts of low frequency analysis, particularly those investigations carried out on biological material or in highly conductive media. Beginning from elementary equations of electrostatics and hydrodynamics, a comprehensive model is devised to account for the screening of a general planar electrode by an ionic double layer. The surface geometry of the planar electrode is left unspecified to include any type of micromachined array. Building on the previous work by DeLacey and White (1982, J. Chem. Soc. Faraday Trans. 2 78, 457) using a variational theorem, we extend their numerical results with compact analytic solutions, analogous to the Debye-Hückel potential for dc systems, but applicable now to dynamic ac experiments. The variational approach generates functions that are not restricted by perturbation expansions or numerical convergence, representing optimal approximations to the exact solutions. Copyright 2000 Academic Press.     

Ion Migration and Frequency-Dependent Dielectric Loss

Abstract

The frequency-dependent dielectric loss due to ion migration in a solvent with a given dielectric function ?(ω) is calculated explicitIy within the following framework:

i) The solvent is treated in the dielectric continuum model

ii) The Navier-Stokes equation is solved for the velocity field

iii) The limiting cases of (a) large ion radius (weak coupling) and (b) point ions (strong coupling) are treated explicitly.

The most clearcut prediction of the theory is that the incremental frequency-dependent conductivity is proportional to ω^¼ at high frequencies, the power law being independent of the form of ?(ω). For arbitrary frequencies, in the limits (a) and (b) above, the incremental frequency-dependent conductivity can be calculated explicitly given the dielectric function of the solvent.     

Streaming Potential and Streaming Current Methods for Characterizing Heterogeneous Solid Surfaces

By monitoring changes in electrokinetic parameters, the streaming potential technique has been used as a method of characterizing heterogeneous surfaces, for example, due to protein adsorption. In general it is assumed that the change in the streaming potential is proportional to the degree of heterogeneity. In this study a simple model of the electrokinetic flow through heterogeneous slit channels has been developed with the goal of comparing the streaming potential and streaming current techniques and determining under what conditions the aforementioned proportionality assumption will produce erroneous results. The flow simulations have shown that, when the streaming potential induces significant flow impedance, a severe deviation from the linear assumption is observed. Since streaming current measurements are unaffected by electrokinetic flow effects, more consistent results are predicted and they are preferred for measurements made in small channels. Additionally it has been shown that the distribution of the heterogeneous coverage has a negligible effect on both the streaming potential and the streaming current in cases where the double-layer overlap is not significant. Copyright 2001 Academic Press.     

Theory of Frequency-Dependent Polarization of General Planar Electrodes with Zeta Potentials of Arbitrary Magnitude in Ionic Media: 2. Applications and Results from Homogeneous and Array Systems of Electrodes

The expressions obtained in the previous paper for electrode polarization are applied to a homogeneous planar electrode and a planar array of electrodes used in the generation of nonuniform fields. The effective far field experienced outside the double layer is computed for both electrodes, and sample spectra are provided. The effective far field expression contains the electrode impedance and the effects of concentration polarization due to the static double layer on the electrode generated by the ζ potential. The effective far field results are compact and contain simple integrals that can be evaluated numerically.     

Streaming current measurements in zirconia-coated capillaries

The electroosmotic flow created in zirconia-modified capillaries has been previously investigated. In this paper, we compared the electroosmotic data set with streaming current measurements and we related all these data through zeta-potential. Streaming current measurements give an excellent indication on the direction and the value of the electroosmotic mobility of an electrolyte/capillary system for a large set of experimental conditions: 2 < pH < 12, 0 < ACN < 80 %, 10(-4) M < [SO(2- )4 ] < 4 x 10(-2) M. A good correlation between zeta-potential from streaming current measurements and zeta-potential from electroosmotic mobility measurements was observed (r2 = 0.95). However, the values obtained from streaming current were always slightly lower than the one calculated from electroosmotic mobility (slope = 0.86, sigma = 0.06). In zirconia-coated capillaries the zeta-potential can be tuned from -50 to +100 mV depending on the composition of the electrolyte.     

XANES Determination of Intraatomic Potentials

A new scheme has been developed for determining the parameters of the local one-electron potential in molecules and solids. The scheme is based on interpretation of the experimental X-ray absorption near edge struucture. The scheme is an extension of the method for solving the inverse problem of XANES theory suggested by one of the authors. In this scheme, oscillator strengths and maximum heights are considered along with the energy and half-width of spectral maxima. The scheme is used for determining the intraatomic potential in the nitrogen molecule.Original Russian Text Copyright © 2004 by Yu. F. Migal and O. M. Kholodova__________Translated from Zhurnal Strukturnoi Khimii, Vol. 45, No. 6, pp. 986–989, November–December, 2004.     

平流式流动电位测试系统的研制

分离膜表面的荷电化显著地影响着膜的分离性能和耐污染能力。因此,定量化表征膜表面电性能具有重要的理论价值和实际意义。作者在前期透过式膜流动电位测试系统研发工作的基础上成功地研制了平流式流动电位测试系统,并且首次将恒电流法测膜体电导引入膜表面ζ(Zeta)电位的确定过程中。以自制不同共混比的合金荷电膜为测试对象,利用该测试系统和经典的Helmholtz-Smoluchowski(H-S)方程及其变体得到了不同pH下的膜表面Zeta电位,从而揭示了膜表面电导、膜体电导对膜表面Zeta电位的贡献,并展示了该流动电位测试系统的有效性。     

Streaming Potential Collection and Data Processing Techniques

To date, no comprehensive comparison of streaming potential coupling coefficient collection or processing techniques has been made. Here, time-varying streaming potential and dc streaming potential data collection and processing techniques are presented and compared. The time-varying streaming potential data include sinusoidal and transient data. The collection techniques include acquiring dc streaming potentials at various pressures, acquiring time-varying streaming potentials at varying pressure, acquiring streaming potentials as a function of frequency, and collecting time-varying raw data. The processing techniques include dc filtering, rms processing, cross-correlation, spectral analysis, and plotting of raw time-varying streaming potential versus raw pressure data. The results show that all processing methods yield the same coupling coefficient within 3%. The analysis also shows that if there is a good signal-to-noise ratio, all processing methods perform satisfactorily. If the signal-to-noise ratio is poor, then the spectral analysis outperforms the other processing methods. The data collection methods are all adequate, but individual applications may make one method superior to another. Copyright 2001 Academic Press.     

Ionic Distribution Coefficients and Electrochemical Potentials

Abstract

A novel “electrochemical ionic distribution coefficient”, i is defined based on Guggenheim's electrochemical potential concept. i correlates the activities of a given ion in different solvents. The definition of i is entirely consistent with the practice to interrelate chemical equilibrium constants in various solvents via the classical ionic distribution coefficient i.     

Magnetic hyperthermia: Potentials and limitations

Despite the fact that the magnetic hyperthermia (MH) has been known for more than 75 years, it is still debated in its clinical applications. The generation of a higher temperature at a tumor is called hyperthermia. There is a different of temperature ranges going from 39 to 40 ?°C up to such high temperatures as 80–90 ?°C. However, due to its high potential, MH is used along with nanoparticles as heat intermediaries in the treatment of cancer. Many Magnetic Nanoparticles (MNPs) with several properties and morphological metallic structures have been useful to magnetics hyperthermia therapy. These MNPs are categorized into two groups; magnetic alloy nanoparticles (MANPs) and magnetic metal oxide nanoparticles (MMONPs). The principal challenges of this method are the control of local tumoral temperature and the increase in nanoparticles heating power. The hyperthermia agents derived from magnetic nanoparticles along with magnetic field. In the recent study, hyperthermia thought, dissimilar types of magnetic nanoparticles for hyperthermia, efficacy for cancer therapy, advances, challenges, and future chances have been examined.     

SWKB Approach to Confined Isospectral Potentials

Recently we had formulated the supersymmetric Wentzel–Kramers–Brillouin (SWKB) quantization rule for one-dimensional confined quantum systems and applied the same to two trigonometric potentials, tangentially limited by infinite walls at x=0 and x=L, viz., V(x)=V ₀cot²(x/L) and the Pöschl–Teller potential, V(x)=V ₀₁cosec²({x/(2L))}+V ₀₂sec²(x/(2L)). Both the potentials have received quite a lot of attention by various authors because of their importance in molecular physics. Though these potentials have been studied in the framework of WKB, BS (Bohr–Sommerfeld), mBS (matrix formulation of BS) formalisms, it was observed that the supersymmetric approach not only rendered the calculations simpler and more transparent, it also reproduced the exact analytical energies in both the cases.In this study, we shall generate isospectral Hamiltonians of the above potentials with the help of a modified form of Darboux's theorem. We shall show that though the new potentials look different from the original ones, and have different eigenfunctions, they too, are confined in the same region of space, and share the same energy spectrum as their original counterparts. This may be of substantial importance in determining the energy spectrum of highly non-trivial systems.     

Zur Definition des effektiven Potentials II

Zusammenfassung Es wird gezeigt, daß die vor einiger Zeit vom Verfasser angegebene Gütedefinition der Näherungslösungen der Schrödingergleichung mit einem schon bekannten Variationsverfahren in Zusammenhang gebracht werden kann, wenn der Begriff des effektiven Potentials eingeführt wird.

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There existes a relation between a definition for the quality of an approximate solution of the Schroedinger equation, earlier given by the auther, and a method of variation, already known, if one introduces the notion effective potential.

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Résumé La définition de qualité donnée précédemment pour les solutions approximatives de l'équation de Schroedinger peut être liée à un procédé variationel déjà connu, par introduction du potentiel effectif.

     

Zur Definition des effektiven Potentials I

Zusammenfassung Es wird gezeigt, daß sich im Rahmen einer naiven Einteilchennäherung kein effektives Potential definieren läßt, sondern die sinnvolle Einführung eines solchen nur dann möglich ist, wenn gewisse Züge des Einteilchenbildes fallen gelassen werden. In diesem Zusammenhang wird eine Definition des Zusatzpotentials angegeben, die auf einem Variationsprinzip basiert und Möglichkeiten aufzeigt, wie das effektive Potential bestimmt werden kann.

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Within the frame of the simple one electron approximation it is not possible to define an effective potential. However, if one drops some precularities of this picture one is able to give a sensible definition of an additional potential based on the variation principle. Possibilities of its calculation are indicated.

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Résumé On montre qu'un potentiel effectif ne peut pas être défini au cadre de l'approximation naïve des particules indépendantes. L'introduction rationnelle de ce potentiel est possible seulement, si l'on abandonne certaines propriétés de cette approximation. Ensuite on donne une définition du potentiel additionel se basant sur le principe de variation et indiquant de possibilités pour le calcul du potentiel effectif.

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Herrn Professor W. Bingel (Göttingen) sei herzlich für Diskussionen und Hinweise gedankt.     

Streaming potential in open and packed fused-silica capillaries

The surface properties of novel stationary phases in packed and open tubular columns for capillary electrochromatography (CEC) were examined by measuring the streaming potential in a home made apparatus. The surfaces investigated include materials such as porous styrenic sorbents and octadecyl-silica as well as fused-silica tubing, in both raw and surface modified forms. Functionalization of the surface was carried out, for instance, by reductive amination or organosilane grafting on to capillary inner wall. The dependence of the streaming potential on pH was examined with aqueous solutions in the pH range from 2.5 to 9.0. Electrokinetic properties of 50 microm I.D. fused-silica capillaries have been determined by both streaming potential and electrosmotic flow measurements. Both methods gave similar pH profiles of the zeta-potential and the isoelectric points. This confirms the viability of our approach to evaluate the specific charged groups of the packing which is one of the important factors influencing electrosmotic flow (EOF) velocity and protein adsorption during a chromatographic run. In addition to bare silica capillaries, styrenic monolithic columns with different surface functionalities, which have been extensively used in our laboratory for CEC separation of peptides and proteins, were employed for comparison of two methods. Plots of zeta potential as a function of percent ACN show a complex behavior, indicating that zeta potential cannot be predicted simply from binary mixture solvent properties. It is demonstrated that the evaluation of the zeta potential by the streaming potential method is nondestructive, relatively fast, without untoward effects introduced by Joule heating and yet another means for the characterization of the surfaces under conditions employed in CEC.     

Streaming potential in a liquid ion-exchange membrane electrode

A streaming potential in a liquid membrane electrode sensitive to nicotinate ion (3-pyridinemonocarboxylate), has been observed during dynamic electrode response measurements carried out by sodium nicotinate step-wise concentration increases. It was possible to separate the streaming potential from the dynamic electrode response and to study it as a function of the flow-rate in the cell and of the nature of the liquid membrane support.A streaming potential was observed with Millipore MF-PH supports (mixed esters of cellulose) but not with Fluoropore (polytetrafluoroethylene bonded to polyethylene net) supports.     

关于汞齐电极的电极电势和可逆性

汞齐电极Ｍｚ +/Ｍ (Ｈｇ)常作为一类可逆电极在物理化学中介绍[1,2 ] ,而对其电极电势和可逆性却少有讨论。本文将主要以钠汞齐电极为例 ,对其作些研究与分析。　　准确称取一定量分析纯Ｈｇ和Ｎａ于玛瑙研钵中混合、研磨成汞齐后 ,用 5倍放大镜观察发现 :反应生成并逸出的氢气泡的数量与Ｎａ含量成正比———含量愈低 ,氢气泡在汞齐与盐液界面形成的速度就愈慢。反之 ,含量愈高 ,形成的速度就愈快。　　由观察可知 ,钠汞齐与ＮａＣｌ水溶液反应　　　　Ｎａ(Ｈｇ) +Ｈ2 ＯＮａＯＨ + 12 Ｈ2 ( 1 )不如纯金属Ｎａ与ＮａＣｌ水溶液反应剧烈…