Three-channel transmission line impedance model for mesoscopic oxide electrodes functionalized with a conductive coating

A three-channel transmission line (TL) impedance model is proposed to address the charge transport behavior of molecular functionalized mesoscopic oxide electrodes at different bias conditions. A full general solution of the three-channel TL for the system is provided in this paper. Selected experimental results of impedance spectroscopy of mesoscopic Al2O3 and TiO2 networks, covered with a monolayer of Ru complex cis-RuLL'(NCS)2 (L = 2,2'-bipyridyl-4,4'-dicarboxylic acid, L' = 4,4'-dinonyl-2,2'-bipyridyl) (Z907), are briefly discussed. It shows that the model constitutes a useful tool for characterizing nanoporous electrodes functionalized with organic conducting layers in the surface. The model makes it possible to determine the separate conductivity of substrate oxide and molecular layer, and interfacial charge transfer, in the functionalized nanostructured electrodes.     

Second-generation supramolecular dendrimer with a defined structure due to orthogonal binding

A second-generation supramolecular dendrimer has been prepared by orthogonal multiple hydrogen bonding. In the first (inner) recognition domain, the interaction of one bis-isocyanuric acid (25) with two branching units (21) that carry complementary Hamilton receptors has been exploited. In the second (outer) generation, the two ADDA (A=hydrogen-bond acceptor, D=donor) receptors of each branching unit (21) have bound complementary DAAD units (4). The problem of limited solubility of the building blocks has been overcome by the introduction of branched ethylhexyl residues and by the use of flexible alkylene or oligo(ethylene glycol) linking chains. The orthogonal binding of the two hydrogen-bonding pairs was elucidated by chemical induced shift NMR titrations, which proved that the two pairs, isocyanuric acid with the Hamilton receptor and ADDA with DAAD, bind preferentially. The formation of the supramolecular self-assembled 1:2:4 dendrimer with a molecular weight of 5065 g mol(-1) was investigated by diffusion NMR spectroscopy.     

Electronic structure of some mesoscopic systems: I. Semiconductor superlattices

As an example of a mesoscopic system, a Kronig-Penney-type model of a semi-infinite GaAs/Ga_1−xAl_xAs superlattice is considered. The effect of the superlattice termination on the formation of a surface state as well as on the density-of-states distributions is discussed. Varying the position of the superlattice surface (i.e., superlattice/substrate interface) within a superlattice period influences strongly the appearance and position of surface states. They occur in particular minigaps for some ranges of the outermost layer thickness only.     

Electronic structure of some mesoscopic systems: II. Electronic composites

We study the electronic properties of a mesoscopic system composed of an array of straight, infinite rods made of an isotropic medium and embedded in a regular way in an isotropic background. Such a composite system has two-dimensional periodicity in the plane perpendicular to the rods. Using a Fourier series expansion, the corresponding Schrödinger equation is solved within the effective-mass approximation. The electronic band structure is computed for the wave vector in the transverse plane, and is illustrated by dispersion curves along the principal directions of the two-dimensional Brillouin zone as well as by the histograms of the density of states. The main result is the appearance of absolute energy gaps in the two-dimensional band structure.     

Composite electrodes of electrochemical capacitors based on carbon materials with different structure

For composite electrodes based on active carbon DCL Supra 30, ordered mesoporous carbon, and synthetic carbon material Sibunit, the electrical double layer capacitance is studied. The original carbon samples are characterized by the methods of gas adsorption, X-ray diffraction, and transmission electron microscopy. The mesoporous structure of the material synthesized by the template method provides the maximum rate of ion transport in pores and demonstrates an insignificant decrease in the specific capacitance (9.5% in an aqueous electrolyte and 1.1% in an nonaqueous electrolyte) with an increase in the polarizing current.     

Computer simulation of polymer networks: mesoscopic heterogeneity of the structure and topological parameters

Samples of networks of reacting bi- and trifunctional monomers have been obtained by the dynamic Monte Carlo method for the two dimensional lattice model. Systems with various densities and numbers of chemical junctions have been studied. The steady-state structural factor, the number of the degree of conversion, and topological parameters of samples appear to depend strongly on the initial (random) spatial configuration and the size of the Monte Carlo base cell. Deviations of structural parameters calculated by ensemble and time averaging are statistically significant, which makes it possible to classify networks of this type as so-called non-ergodic fortuitous media that exhibit this property for scales of 10² nm. Newly developed facilities for topological analysis allow one to observe the kinetics of changes in individual components of the system: trees, circuits, and other more complex structures.Papers presented in the section Physical Chemistry of this issue are based on the materials delivered at the XII Seminar on Intermolecular Interactions and Conformation of Molecules, Khar'kov, October 3–8, 1994.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 7, pp. 1226–1232, July, 1995.The work was financially supported by the Russian Foundation for Basic Research (Project No. 9503-08170a).The authors are grateful for Professor J. G. H. Joosten of Leiden University for helpful critical comments.     

Microelectrogravimetry with wire-type electrodes

Summary Electrogravimetry with a simple wire cathode dates back more than 70 years. Work may have been discouraged by factors such as long deposition times, difficult technique and, sometimes, low precision. A simple cell that employs a rapidly-rotating helical cathode has now been designed. Easily constructed, the system is comparatively easy to use. The cathode, merely a 10–15-cm length of 0,05-cm platinum wire, is easily replaceable if damaged or lost. Factors that affect precision, accuracy, and speed of copper deposition by the Milner-Whittem procedure have been studied. An adaption of this procedure has been found to permit the recovery of 99.5% of 3–10 mg of copper in approximately 90 min. Similar results were obtained for copper in standard samples of bronze. After the copper deposition, electrolysis was continued to determine tin plus lead. Here the recovery was 97.4+0.8%.

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Zusammenfassung Die seit mehr als 70 Jahren bekannte Elektrogravimetrie mit einer einfachen drahtförmigen Elektrode wurde wegen der langen Abscheidungszeit, umständlicher Handhabung, manchmal geringer Genauigkeit und ähnlicher Umstände in den Hintergrund gedrängt. Nun wurde eine einfache Elektrolysezelle mit einer rasch rotierenden Helix-Kathode hergestellt, die auch einfach zu handhaben ist. Diese nur aus eineni 0,05 cm starken, 10–15 cm langen Platindraht bestehende Kathode ist auch leicht erScizbar. Umstände, die die Genauigkeit und Geschwindigkeit der Kupferabscheidung nach dem Verfahren von Milner und Whittem beeinflussen, wurden untersucht. Dieses Verfahren wurde soweit verbessert, daß 3–10 mg Kupfer in etwa 90 min zu 99,5% bestimmt werden können. Ähnliche Ergebnisse erhält man auch bei der Bestimmung des Kupfergehaltes in Bronze-Standardproben. Nach der Abscheidung des Kupfers wurde die Elektrolyse fortgeScizt, um Zinn und Blei zu bestimmen. Hierbei wurden 97,4±0,8% wiedergefunden.

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Presented at the International Symposium on Microtechniques 1977, held at Davos, Switzerland, 21–25 May 1977.     

Imaging mesoscopic nuclear spin noise with a diamond magnetometer

Magnetic resonance imaging can characterize and discriminate among tissues using their diverse physical and biochemical properties. Unfortunately, submicrometer screening of biological specimens is presently not possible, mainly due to lack of detection sensitivity. Here we analyze the use of a nitrogen-vacancy center in diamond as a magnetic sensor for nanoscale nuclear spin imaging and spectroscopy. We examine the ability of such a sensor to probe the fluctuations of the "classical" dipolar field due to a large number of neighboring nuclear spins in a densely protonated sample. We identify detection protocols that appropriately take into account the quantum character of the sensor and find a signal-to-noise ratio compatible with realistic experimental parameters. Through various example calculations we illustrate different kinds of image contrast. In particular, we show how to exploit the comparatively long nuclear spin correlation times to reconstruct a local, high-resolution sample spectrum.     

Model description of specific adsorption of two anions on electrodes

Simultaneous specific adsorption of two anions on the electrode surface is considered. Calculations involve the use of the Frumkin adsorption isotherm for each anion and a model that describes the electric double layer structure based on one or two Helmholtz planes. Dependences of the ion adsorption on both the electrode potential and the solution composition are calculated for different electrode charges, ion sizes, and capacitance characteristics of the electric double layer.     

Towards a mesoscopic model of water-like fluids with hydrodynamic interactions

We present a mesoscopic lattice model for non-ideal fluid flows with directional interactions, mimicking the effects of hydrogen bonds in water. The model supports a rich and complex structural dynamics of the orientational order parameter, and exhibits the formation of disordered domains whose size and shape depend on the relative strength of directional order and thermal diffusivity. By letting the directional forces carry an inverse density dependence, the model is able to display a correlation between ordered domains and low density regions, reflecting the idea of water as a denser liquid in the disordered state than in the ordered one.     

Expeditious assembly of mesoscopic metallocycles

Very large chiral metallocycles with tunable cavities in the range of 0.9-22 nm were efficiently assembled from the requisite metal- and ligand-terminated oligomers that are built from the 2,2'-diacetoxy-1,1'-binaphthyl-3,3'-bis(ethyne) bridging ligand and trans-Pt(PEt3)2 metal connector. These unprecedented nanoscopic and mesoscopic molecular metallocycles have been characterized with 1H, 13C{1H}, and 31P{1H} NMR spectroscopy, microanalysis, IR, UV-vis, and circular dichroism spectroscopies, MALDI-TOF MS, and size exclusion chromatography (SEC). SEC results indicated that the metallocycles appear to be much more compact and rigid than the metal- and ligand-terminated oligomers. The present molecular metallocycles provide interesting building blocks for the construction of larger functional structures that cannot be accessed from a top-down approach.     

Single‐chain nanoparticles with well‐defined structure via intramolecular crosslinking of linear polymers with pendant benzoxazine groups

Controlled intramolecular collapse of linear polymer chains with crosslinkable groups is an efficient way to prepare single‐chain nanoparticles in the size range of 5–20 nm. However, the nature of the crosslinking group is critical. In present study, poly(styrene‐co‐chloromethyl styrene) [P(St‐co‐CMS)] was synthesized via reversible addition‐fragmentation chain transfer (RAFT) polymerization and then was converted into polystyrene azide (PS? N₃). Polystyrene containing benzoxazine side groups [P(St‐co‐BS)], which can be used as the precusor for the later intramolecular collapse, was obtained from PS? N₃ and 3‐(4‐(prop‐2‐ynyloxy)phenyl)‐3,4‐dihydro‐2H‐benzo[e][1,3]oxazine (P‐APPE) via the method of click chemistry. The sub‐20 nm polymeric nanoparticles with well‐defined structure via thermally intramolecular crosslinking of P(St‐co‐BS) were prepared. The structure change from the linear polymers to the single‐chain nanoparticles was confirmed by nuclear magnetic resonance (NMR), Fourier transform infrared (FTIR), and gel permeation chromatography (GPC). The morphology and the dimension of the nanoparticles were characterized by using transmission electron microscope (TEM), atomic force microscopy (AFM), as well as dynamic light scattering (DLS). The results reveal that the size of the nanoparticles can be regulated by changing the molecular weight of the precursors and the amount of pendant benzoxazine groups by the use of controlled polymerization techniques. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Iodide determination with chalcogenide glass electrodes

Journal of Solid State Electrochemistry - The fabrication and characterisation of potentiometric chalcogenide glass electrodes with selectivity for iodide in aqueous media are reported. While such...     

Potential-induced structure changes of oligopyridine adlayers on Au(111) electrodes

The structure of a bisterpyridine-like oligopyridine (abbreviated as 2,4'-BTP) monolayer on Au(111), adsorbed from an acetone solution, was studied by in situ scanning tunneling microscopy and cyclic voltammetry in aqueous 0.1 M H2SO4. Short-range ordered adsorption with an average distance between the individual molecules of about 2 nm was observed only at electrode potentials positive of +0.4 V vs SCE, whereas at more negative potentials, no order could be found. With the help of Cu underpotential deposition, a potential-induced, fast, and fully reversible structure transition within the organic monolayer was identified at about +0.4 V vs SCE. At negative potentials the molecules apparently cluster together and consequently current-potential curves resemble those for a bare gold surface, whereas for E>+0.4 V vs SCE the molecules are spread over the entire surface in a hexagonal, close-packed fashion. This may have interesting consequences for switching between different template structures.     

Micro- and mesoscopic structure of poly(vinyl alcohol) gels determined by neutron and light scattering

We studied the structure of poly(vinyl alcohol) (PVA) gels formed in mixtures of dimethyl sulfoxide (DMSO) and water using several scattering techniques such as wide-angle neutron scattering (WANS), small-angle neutron scattering (SANS), ultra-small-angle neutron scattering (U-SANS) and light scattering (LS) to cover a very wide Q range from 10^-4 to 10 Å^-1. The WANS measurements have revealed that the cross-linking points of the gels are crystallites, and the size and its distribution have been evaluated by the SANS measurements. The SANS results have also shown that the structure observed in the low Q range below 10^-2 Å^-1 is dominated by a liquid–liquid-phase separation. The early stage of the phase separation has been studied in detail using the time-resolved LS technique, while the late stage has been investigated by the U-SANS technique because the LS measurements cannot access the opaque samples. On the basis of the results, we present a quantitative sketch of the structure of the PVA gel.     

Supercapacitor carbon electrodes with high capacitance

Electrochemical behavior of electrodes on the basis of CH900-20 activated carbon (AC) cloth has been studied in concentrated sulfuric acid solution. Cyclic voltammetric curves have been studied in the reversibility range (from 0.1 to 0.9 V RHE) and in the deep cathodic charging potential range (from –0.8 to 1 V RHE). It has been shown that electric double layer (EDL) charging occurs in the reversibility range, while faradaic processes of hydrogen intercalation into AC carbon take place in the range of negative potentials (←0.1 V). The intercalation process is governed by slow solid-phase hydrogen diffusion. The specific charge value grows at an increase in concentrated sulfuric acid solution. The mechanism of double intercalation of sulfuric acid and hydrogen into the AC material is suggested. On the basis of the reached specific discharge capacitance of 1,560 C/g (or 1,110 F/g) and Faraday's law, it has been concluded that the compound of C₆H is formed in the limiting case of deepest cathodic charging. The obtained data have been used in a mathematical charge–discharge model for an AC electrode taking into account the EDL charging and the hydrogen intercalation. The galvanostatic recharge curves have been calculated in the diapason of currents by the developed model.     

Plasma torch with liquid metal electrodes

In order to eliminate the negative effect of erosion processes on electrodes in arc plasma generators, a new scheme of arc discharge was proposed in which the surface of a molten metal acts as electrodes. A plasma reactor was designed on the basis of this concept. The electrophysical characteristics of such a discharge in steam and air as plasma gases were studied. Experiments on destruction of toxic polychlorinated biphenyls and steam coal gasification were performed.     

Automated potentiometric analysis with selective electrodes

An automated potentiometric analyzer based on a residual-chlorine electrode has been developed that can determine chlorine concentrations of a 4–75 ppb (±2 ppb, standard deviation 0.6–1.9 ppb). A microcomputer-controlled digital buret delivers a predetermined number of aliquots of standard, and the electrode measures the potential of the test solution after each addition. An arithmetic processing unit transforms the acquired potentiometric data to the Gran (antilog) domain; the microcomputer then calculates a set of equivalence-point estimates and, using an error function criterion, selects the best estimate. The instrument includes a digital buret, 8080 microcomputer, arithmetic processing unit, real-time clock, video display, and 16-character key pad; it uses a modified version of the computer language BASIC compiled and programmed into Programmable Read-Only Memory (PROM). Although this system was designed to assay residual chlorine in water, the analyzer can also function as a digital pH (or millivolt) meter or, with minor software modifications, serve as a general-purpose instrument using any appropriate electrode system.