Transference conductivity measurement

In the case of small ions, Hittorf transference cell measurements may be combined with conductivity data to give the mobility of the ion, that is, the velocity per unit potential gradient in solution, or its equivalent conductance. Alternatively, these may be measured more directly by the moving boundary method. 

Despite the results from various experiments such as transference number measurements, polarographic studies, spectroscopic measurements, and dielectric relaxation studies in addition to conductivity measurements, unilateral triple-ions remain a matter of debate. For experimental examples and other hypotheses for the interpretation of conductance minima the reader is referred to Ref. [15] and the literature cited there. 

Jacobs et al. [59,925,926] (Fig. 17). While this scheme conveniently summarizes many features of the observed behaviour, a number of variations or modifications of the mechanisms indicated have been proposed. Maycock and Pai Vemeker [924,933] emphasize the possible role of point defects and suggest, on the evidence of conductivity measurements, that the initial step may be the transfer of either a proton or an electron. Boldyrev et al. [46] suggest that proton conduction permits rapid migration of HC104 within the reactant and this undergoes preferential decomposition in distorted regions. More recently, the ease of proton transfer and the mobilities of other species in or on AP crystals have been investigated by a.c. [360] and d.c. [934] conductivity measurements. Owen et al. [934] could detect no surface proton conductivity and concluded that electron transfer was the initial step in decomposition. At the present time, these inconsistencies remain unresolved. 

As outlined at the beginning of this chapter, combined photocurrent and microwave conductivity measurements supply the information needed to determine three relevant potential-dependent quantities the surface concentration of excess minority carriers (Aps), the interfacial recombination rate (sr), and the interfacial charge-transfer rate ( r). By inserting the... 

From the above-made review of literature, one may infer that the interaction of metastable atoms of rare gases with a surface of semiconductors and dielectrics is studied, but little. The study of the mechanism of transferring energy of electron-excited particles to a solid body during the processes under discussion is urgent. The method of sensor detection of rare gas metastable atoms makes it possible to obtain new information about the heterogeneous de-excitation of metastable atoms inasmuch as it combines high sensitivity with the possibility to conduct measurements under different conditions. 

Trioctylmethylammonium chloride [7] has been widely used as a phase transfer catalyst. This compound is slightly soluble in water and forms aggregates at very low concentrations (Okahata et al., 1977). Figure 3 shows surface tension data, which indicate aggregation occurring at 10-4-10-5 M. The dye probe method and conductance measurements suggest that the... 

Whether using dilution or concentration methods, care must be taken to exclude atmospheric water from the cell during all operations. Typically, all-glass systems are employed with an atmosphere of dry nitrogen or argon, and any transfers of salt or solution are performed in a glovebox. Care must be taken to use anhydrous salts of highest purity. If the salt is not analyzed before use, conductance measurements before and after successive purifications of the material should be compared as a check on purity 31>. 

Conductivity measurements are often the first to be carried out on an electrolyte however, they provide information only on the total transport of charge. Even in a fully dissociated electrolyte, such measurements do not differentiate between the current carried by the cations and the anions. Transport or transference measurements attempt to probe more deeply into the movement of species in electrolytes. 

Electrical conductivity measurements on silicate melts indicate an essentially ionic conductivity of unipolar type (Bockris et al., 1952a,b Bockris and Mellors, 1956 Waffe and Weill, 1975). Charge transfer is operated by cations, whereas anionic groups are essentially stationary. Transference of electronic charges (conductivity of h- and n-types) is observed only in melts enriched in transition elements, where band conduction and electron hopping phenomena are favored. We may thus state that silicate melts, like other fused salts, are ionic liquids. 

Thermal conductivity measures the rate of transfer of heat by conduction through unit thickness, across unit area for unit difference of temperature. It is measured as calories per second per square centimeter for a thickness of one centimeter and a temperature difference of 1°C. Its units are cal/cm sec.°K or W/cm°K. 

There are two main varieties of bulk conductivity detectors contact and contactless. In a contact conductivity detector, the electrodes contact the column effluent directly. The electrodes are usually made of stainless steel, platinum, or gold in order to minimize electrochemical reactions, but they are still subject to fouling over time. In the absence of electrochemical reactions, there is no charge transfer between the solution and the electrodes, so the conductivity measurement is made with an oscillating or alternating voltage. 

Films have been deposited using selenourea and an ammonia-complexed solution at 65°C [96]. Zincblende CdSe was obtained with an optical spectrum corresponding to a bandgap of 1.84 eV (the bulk room-temperature bandgap of zincblende CdSe is ca. 1.8 eV). Analysis of electrical conductivity measurements indicated charge transfer occurred via a variable hopping mechanism through fairly deep states (a level 0.29 eV below the conduction band was found from these measurements). 

The extensive disorder in any DNA structure leads to a myriad of mechanisms for electron transfer in rate constant measurements, and for electron or hole transport in conduction measurements. The major difficulties of understanding electron motion mechanisms in DNA are then of two sorts. First, the different kinds of disorder make reproducible measurements difficult to obtain. Second, the different sorts of interactions (Coulombic, vi-bronic, polarization, dynamical relaxation) make well-defined models difficult to formulate and deceptive in their predictions. 

LB films prepared from an azabenzene-containing surfactant donor-TCNQ acceptor and transferred to solid substrates Absorption spectra, polarized microscopy, and conductivity measurements... 

LB films prepared from tridecylmethyl-ammonium Au-(dmit)2 and H2dmit = 4,5-dimercapto-l,3-dithiol-2-thione, transferred to hydrophobized glass substrates, and oxidized (by Br2 or electrochemicaily) Absorption spectra and temperature-dependent conductivity measurements... 

LB films prepared from alternating layers of long-chain TCNQ and long-chain TTF and transferred to glass substrates Absorption spectra and conductivity measurements... 

LB films prepared from metal complex salts (R+)2[Ni(dmit)2]2, (R +)2-[Ni(mnt)2]2 and R+[Ni(dmit)2]- (where R = (CH3)2 (C12H25)2N+), transferred to substrates, and exposed to bromine vapor Surface-potential and conductivity measurements Lateral d.c. conductivities of bromide exposed films were in the 0.001 to 0.28 S cm 1 range 767... 

LB films prepared from poly(thiophene-3-acetic acid)-stearylamine and from sulfonatedpolyaniline-stearylaminepolyion complexes, transferred to substrates, and doped by acid FTIR, X-ray diffraction, and conductivity measurements Lateral d.c. conductivities of acid-doped films as high as 0.05 S cm"1 were obtained 768, 769... 

Pyrrole polymerized at the interface of non-polymerizable 3-octadecanoyl pyrrole and transferred to substrates to form LB films FTIR and conductivity measurements Lateral d.c. conductivities as high as 0.1 S cm 1 were obtained 769, 770, 771... 

LB film prepared from stearic acid and containing TBTTF-Zn(dmit)2 charge transfer complex (and oxidized by iodine exposure) Absorption, FTIR spectroscopy, lowangle X-ray diffraction, conductivity measurements Maximum conductivities perpendicular and parallel to the LB film were determined to be 10-3Scm-t and4.3xl0 l Scm-1 122... 

LB films prepared from ironfUI) stearate, transferred to solid substrates, dried, exposed to hydrochloric add in a desiccator, and subsequently exposed to pyrrole vapor Absorption spectroscopy, scanning electron microscopy, and conductivity measurements Lateral conductivity as high as t.25 S cm" was measured 123... 

Fig. 10.15 Conductance per ion pair of metal-ammonia solutions. The ratio of electrical conductivity to the concentration of metal (equivalent conductance) is shown as a function of concentration. O represent data of Kraus (1921) and data of Dye et al. (I960), both at 240 K and in Na-NH3 solutions. + and x represent the equivalent conductances assigned to positive and negative carriers respectively by Dye on the basis of transference-number measurements. From Cohen and Thompson (1968).

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