Electrical properties field frequency

A simple thin film technique has been developed to measure the electrical properties of polyelectrolyte solutions under sinusoidal electric fields of 100-500 v/cm at frequencies of. 10-10 KHz. Ohmic heating is largely avoided by the rapid transfer of heat to the electrodes and by the high surface to volume ratios. The resulting temperature is not sufficient to damage the medium. Current and voltage wave forms are monitored directly so that dispersion and nonlinear phenomena of the medium can be viewed directly as functions of frequency, voltage, and concentration of the solution. Possible mechanisms for the observed phenomena are discussed. 

The experimental measures of these molecular electric properties involve oscillating fields. Thus, the frequency-dependence effects should be considered when comparing the experimental results . Currently, there are fewer calculations of the frequency-dependent polarizabilities and hyperpolarizabilities than those of the static properties. Recent advances have enabled one to study the frequency dispersion effects of polyatomic molecules by ab initio methods In particular, the frequency-dependent polarizability a and hyperpolarizability y of short polyenes have been computed by using the time-dependent coupled perturbed Hartree-Fock method. The results obtained show that the dispersion of a increases with the increase in the optical frequency. At a given frequency, a and its relative dispersion increase with the chain length. Also, like a, the hyperpolarizability y values increase with the chain length. While the electronic static polarizability is smaller than the dynamic one, the vibrational contribution is smaller at optical frequencies. ... 

Table 2.1 List of molecules studied with four-component methods. The fourth column lists quantities, which have been investigated primary data P = (total electronic energies (E), orbital energies e,-, population analyses PA), ionization energies IE, election affinities EA, atomization energies A, spectroscopic data S = (equilibrium distance re, dissociation energy De, frequencies/wave numbers coe, bond angles 0), electric properties E = (dipole moment fx, quadrupole moment 0, dipole polarizability a, infrared intensities I, excited states ES, electric field gradients EFG, energetics of reaction R.

The electrical properties of the films were determined on aluminium/insu-lator/gold (MIM) structures. The capacitance was measured with a LCR Meter (Agilent 4284 A) at a frequency of 1 kHz. The specific resistance and the breakdown field strength were measured using a Source-Measure-Unit (SMU, Keithley 6430). The film thickness was determined by scanning electron microscopy (SEM). 

Viscosity and density of the emulsion, dispersion, water content, electrical properties as well as the stability of the protective films considerably influence the efficiency of electrical separation. However, the main factor is the intensity of the electrical field. The electrical separators are operated at the current industrial frequency (50 Hz for Europe and 60 Hz for North America), rarely by constant current. The voltage on the electrodes in the separators ranges from 10,000 to 45,000 V. 

Electrical fringe fields often do penetrate into the sample. The sample s dielectric properties affect the parallel capacitance, Co, and thereby the frequency shift. The QCM can probe dielectric properties and viscoelastic properties at the same time. 

In the same frame of the time-dependent two-term approximation, kinetic problems in quite different time-dependent fields have been dealt with (Wilhelm and Winkler, 1979 Winkler, 1993). So, for example, the temporal evolution of the kinetic properties initiated by jumplike and continuous field transitions between steady states, by pulselike field alterations, or by decaying electric fields and the periodic evolution (Winkler, 1993) caused by the action of high-frequency electric fields in a wide range of field frequencies should be mentioned in this context. 

Nonequilibrium electro-optical properties of polymers with mesogenic side groups are also very distinctive. In alternating electric fields, low-frequency dispersion of the Kerr effect is observed. The range of dispersion depends on the molecular weight of the fraction, just as for lyotropic polymers. Fig. 9 shows the dependence of the relative value of the Kerr constant at the field frequency V and at v=0 on the field frequency for solutions of... 

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