Conductivity techniques

After starting his own laboratory in 1982, the author built microwave measurement facilities with his collaborators and resumed research on microwave electrochemical phenomena. While the potential of combining photoelectrochemistry with microwave conductivity techniques became evident very soon,6,7 it was some time before microwave experiments could be performed at semiconductor electrodes under better-defined microwave technical conditions.8... 

The increased lifetime of photogenerated minority carriers can be measured experimentally. This is shown for a single-crystal ZnO-electrode (Fig. 22). Both the stationary PMC peak and the potential-dependent lifetime in the depletion region, measured with transient microwave conductivity techniques are plotted.25 It is seen that the stationary PMC peak coincides with a peak in the lifetime of minority carriers. This... 

KI Al-Malah, MOJ Azzam, RM Omari. Emulsifying properties of BSA in different vegetable oil emulsions using conductivity technique. Food Hydrocolloids 14 485-490, 2000. 

Farkas and Farkas (32) examined the kinetics of the exchange and hydrogenation of benzene catalyzed by platinized platinum foil at room temperature. The occurrence of isotope exchange was detected by the thermal conductivity technique. They reported (i) that the exchange reaction was only a little faster than hydrogenation and (ii) that exchange... 

Diagnostic indications for nerve biopsy have become less frequent with improvements in EMG and nerve conduction techniques and the advent of specific molecular and biochemical tests for many inherited and acquired neuropathies. However, nerve biopsy does remain useful for diagnosis of vasculitis and amyloidosis, and plays an important role in research. 

Small ion association constants (down to 5 or so) can be determined with relatively high precision by conductance techniques. The magnitude of these constants is related to many of the factors that determine mobilities. 

Ng and Assirelli have carried out a mixing study in batch stirred vessels with working volumes of 3 L to 20L using a fiber-optic UV-vis monitoring technique. Bromophenol blue sodium salt was used as a non-reactive tracer. The results on traditional Rushton turbines and 45° angled pitched blade turbines showed good agreement with a typical conductivity technique and a correlation proposed in literature. 

Mozer AJ, 8ariciftci N8, Pivrikas A, Osterbacka R, Juska G, Brassat L, Bassler H (2005) Charge carrier mobility in regioregular poly(3-hexylthiophene) probed by transient conductivity techniques a comparative study. Phys Rev B 71 035214... 

Electron attachment to O2 has been investigated in supercritical hydrocarbon fluids at densities up to about 10 molecules/cm using the pulsed electric conductivity technique [110], and the results have been explained in terms of the effect of the change in the electron potential energy and the polarization energy of 2 in the medium fluids. In general, electron attachment to O2 is considered to be a convenient probe to explore electron dynamics in the condensed phase. 

At high field strengths a conductance Increase Is observed both In solution of strong and weak electrolytes. The phenomena were discovered by M. Wien (6- ) and are known as the first and the second Wien effect, respectively. The first Wien effect Is completely explained as an Increase In Ionic mobility which Is a consequency of the Inability of the fast moving Ions to build up an Ionic atmosphere (8). This mobility Increase may also be observed In solution of weak electrolytes but since the second Wien effect Is a much more pronounced effect we must Invoke another explanation, l.e. an Increase In free charge-carriers. The second Wien effect Is therefore a shift in Ionic equilibrium towards free ions upon the application of an electric field and is therefore also known as the Field Dissociation Effect (FDE). Only the smallness of the field dissociation effect safeguards the use of conductance techniques for the study of Ionization equilibria. 

The magnitude of the errors in determining the flat-band potential by capacitance-voltage techniques can be sizable because (a) trace amounts of corrosion products may be adsorbed on the surface, (b) ideal polarizability may not be achieved with regard to electrolyte decomposition processes, (c) surface states arising from chemical interactions between the electrolyte and semiconductor can distort the C-V data, and (d) crystalline inhomogeneity, defects, or bulk substrate effects may be manifested at the solid electrode causing frequency dispersion effects. In the next section, it will be shown that the equivalent parallel conductance technique enables more discriminatory and precise analyses of the interphasial electrical properties. 

The rates of complex formation and ligand substitution reactions of the polymer-bound Co(III) complexes depend on the dynamic property of the polymer domains. Reports on the kinetics of complex formation and ligand substitution of macromolecule-metal complexes are, however, relatively scarce. They include investigations on the complexation of poly-4-vinylpyridine with Ni2+ by the stopped conductance technique 30) and on a ligand substitution reaction of the polymer-bound cobalt(III) complexes 31>. 

Methyltin halides dissolved in solvents of type (i) do not enter into a noticeable donor-acceptor interaction with the solvent the tin coordination number is, therefore, unaffected. At the same time, conductivity techniques (78, 79, 140, 141, 47, 24) show that methyltin halides do not ionize in solvents such as nitromethane and nitrobenzene whose dielectric permeabilities are high (35.9 and 34.8, respectively). In this section the halide structures are discussed only in solvents of type (i). When they are dissolved in solvents of type (ii), the halides enter into complex formation these systems are dealt with under complexation of methyltin halides (see Section IV). 

TC/BG BC/BG SC/BG BC/TG PR-TRMC Top contact/bottom gate Bottom contact/bottom gate Sandwich contact/bottom gate Bottom contact/top gate Pulse-radiolysis time-resolved microwave conductivity technique... 

The conductivity technique used to study the pyridine initiation process could not be applied to aliphatic amines because they react appreciably with weak acids. However, some information was gained from experiments in which further monomer was added to completed polymerizations. 

Early experiments in liquids were quite variable for many reasons. The conductivity technique, which was used in the gas phase to measure dose, was not applicable to the liquid phase. Reactions were measured using dissolved radium salts or radon gas as the ionization source. Some thought the chemistry was due to the reactions with radium however, it was soon recognized that it was the emitted rays that caused the decomposition. Both radium and radon could cause radiation damage. Because the radon would be partitioned between the gas and liquid phase, the amount of energy that was deposited in the liquid depended critically on the experimental conditions such as the pressure and amount of headspace above the liquid. In addition, because the sources were weak, long irradiation times were necessary and products, such as hydrogen peroxide, could decompose. 

Beck G. (1983) A picosecond pulse-conductivity technique for the study of excess electron reactions. Radiat Phys Chem 21 7-11. 

Warman JM, de Haas MP. (1991) Time-resolved conductivity techniques, DC to microwave. In Tabata Y (ed.), Puke Radiolysis, pp. 101-133. CRC Press, Boca Raton. 

Hoofman RJOM, van der Laan GP, de Haas MP, Tanigaki K. (1997) Charge migration in pulse-irradiated undoped C60 powder studied with the time-resolved microwave conductivity technique. Synth Met 86 2355-2356. 

If still higher fields are desired, it is possible to use well-known, though expensive, super-conducting techniques up to 18 T, while maintaining high homogeneity. Such fields represent the state of the art for high-resolution... 

Although it is essentially a conductivity technique, the experimental setup is very similar to that used for optical absorption measurements. In simple terms, the attenuation of the amplitude of the microwave resulting from its passage through the irradiated system is measured. Actually, the microwaves are reflected back through the medium by a metal plate at the back of the cell, but because micro-waves undergo reflection at any dielectric discontinuity, such as the gas-liquid interface at the front of the cell, interference effects arise due to the coherent nature of the microwave radiation. 

A further example of Eqs 6 and 7 has been studied using the time-resolved conductance technique [53]. It involves the addition to alkenes of Cl, e.g. Scheme 1, in which the intermediate )9-chloroalkyl radical undergoes C-Cl heterolysis with het = 3.1-3.5 X 10 s to give the short-lived (r < 20 ns) alkene-type radical cation >C -C H2 which is trapped by the nucleophile water yielding >C -CH20H/... 

Measured using the time-resolved AC or DC (time resolution < 10 ns) conductance technique. In all cases the concentration of the alkene was varied to make sure that the formation of the SO4 adduct was not rate-limiting. 

Fortunately there is available a simple conductance technique for monitoring ion pair—free ion equilibria, which, while being unable to give information about different ion pairs, readily produces data on the proportion of free ions to all ion pairs. The equilibrium is treated as approximating to the dissociation of a weak electrolyte, e.g. acetic acid in water. 

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