Electrical Properties Dipoles

The electrical dipole of the crystalline phosphates caused them to be of interest as potential anticaking and antistatic agents. It was relatively easy to induce a dipole into a crystal with a smaller diameter and a respectable aspect ratio of about 50. This aspect ratio is small when compared to many mineral fibers, but phosphate fibers could be dusted on charged surfaces to kill charge on a surface. Some crude experiments with charged sheets and cloth indicated that the fibers might be useful to counteract static electrical charges. 

All crystalline phosphate fibers considered in the Phosphate Fibers Project were probably piezoelectric. Although all were not tested for piezoelectric behavior, all were birefringent when viewed in a polarized field of a petrographic microscope. Few, if any, phosphate crystals that are birefringent are not also piezoelectric. 

Griffith, Caking of Particular Solids, VCH Publ. Co., New York (1992). 

Simpson, in Asbestos—Properties, Applications and Hazards, Vol. II (S. S. Chissick and R. Derricott, eds.), Wiley, New York (1983). 

A Field Guide to Minerals, Rocks, and Precious Stones, Cathey Books, Lx)ndon (1976). 

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The interactions of a gas - normally a mixture - with the surface of a solid material can be fairly complex. This is due to the fact that the gas molecules can vary considerably in size, structure and electric properties (dipole and quadrupole moments), and also the surface of the solid may offer different types of sites for adsorption, reflected in both the pore spectrum and the enthalpies of adsorption, cp. Chap. 1, [0.4-0.6]. Hence one has to expect that interactions between adsorbed molecules of different type will be different from their possible interactions in a bulk gas or liquid phase. 

Equations (6.5) and (6.12) contain terms in x to the second and higher powers. If the expressions for the dipole moment /i and the polarizability a were linear in x, then /i and ot would be said to vary harmonically with x. The effect of higher terms is known as anharmonicity and, because this particular kind of anharmonicity is concerned with electrical properties of a molecule, it is referred to as electrical anharmonicity. One effect of it is to cause the vibrational selection mle Au = 1 in infrared and Raman spectroscopy to be modified to Au = 1, 2, 3,. However, since electrical anharmonicity is usually small, the effect is to make only a very small contribution to the intensities of Av = 2, 3,. .. transitions, which are known as vibrational overtones. 

Some electrical properties are shown in Table 3. Values of other parameters have been pubflshed (146). Polymorphism of the PVDF chains and the orientation of the two distinct dipole groups, —CF2— and —CH2—, rather than trapped space charges (147) contribute to the exceptional dielectric properties and the extraordinarily large piezoelectric and pyroelectric activity of the polymer (146,148,149). 

The beryllium-fluorine bond is also highly ionic in character. However, there are two such Be-F bonds and the electrical properties of the entire molecule depend upon how these two bonds are oriented relative to each other. We must find the geometrical sum of these two bond dipoles. 

Dipole Moments, Polarography, and Other Electrical Properties... 

Five large basis sets have been employed in the present study of benzene basis set 1, which has been taken from Sadlej s tables [37], is a ( ()s6pAdl6sAp) contracted to 5s >p2dl >s2p and contains 210 CGTOs. It has been previously adopted by us in a near Hartree-Fock calculation of electric dipole polarizability of benzene molecule [38]. According to our experience, Sadlej s basis sets [37] provide accurate estimates of first-, second-, and third-order electric properties of large molecules [39]. 

In some crystalline substances the centers of gravity of positive and negative charges do not coincide in the first place, i.e. permanent dipoles are present. Concerning the electrical properties, the following cases can be distinguished. 

Quantum mechanical calculations are appropriate for the electrons in a metal, and, for the electrolyte, modern statistical mechanical theories may be used instead of the traditional Gouy-Chapman plus orienting dipoles description. The potential and electric field at any point in the interface can then be calculated, and all measurable electrical properties can be evaluated for comparison with experiment. 

It should be noted that the dynamics studied by fluorescence methods is the dynamics of relaxation and fluctuations of the electric field. Dipole-orientational processes may be directly related to biological functions of proteins, in particular, charge transfer in biocatalysis and ionic transport. One may postulate that, irrespective of the origin of the charge balance disturbance, the protein molecule responds to these changes in the same way, in accordance with its dynamic properties. If the dynamics of dipolar and charged groups in proteins does play an important role in protein functions, then fluorescence spectroscopy will afford ample opportunities for its direct study. 

Abstract Although the electronic structure and the electrical properties of molecules in first approximation are independent of isotope substitution, small differences do exist. These are usually due to the isotopic differences which occur on vibrational averaging. Vibrational amplitude effects are important when considering isotope effects on dipole moments, polarizability, NMR chemical shifts, molar volumes, and fine structure in electron spin resonance, all properties which must be averaged over vibrational motion. 

Methods for determining permanent dipole moments and polarizabilities can be arbitrarily divided into two groups. The first is based on measuring bulk phase electrical properties of vapors, liquids, or solutions as functions of field strength, temperature, concentration, etc. following methods proposed by Debye and elaborated by Onsager. In the older Debye approach the isotope effects on the dielectric constant and thence the bulk polarization, AP, are plotted vs. reciprocal temperature and the isotope effect on the polarizability and permanent dipole moment recovered from the intercept and slope, respectively, using Equation 12.5. 

Another approach developed by McIntosh and his co-workers 112-117) has been to measure the electrical properties of the adsorbates while they are adsorbed it is found that changes in the capacitance curves take place at the monolayer point. However, interpretation of the data to provide, say, the polarizability of the adsorbed species has proved to be difficult. An apparent dipole moment of infinity was obtained for sulfur dioxide adsorbed on rutile. It was concluded 116) that no satisfactory way of obtaining the apparent electrical properties of adsorbed matter has been developed, and until this is achieved, no great clarification of the observations seems likely. 

The dipole moment is a fundamental property of a molecule (or any dipole unit) in which two opposite charges are separated by a distance . This entity is commonly measured in debye units (symbolized by D), equal to 3.33564 X 10 coulomb-meters, in SI units). Since the net dipole moment of a molecule is equal to the vectorial sum of the individual bond moments, the dipole moment provides valuable information on the structure and electrical properties of that molecule. The dipole moment can be determined by use of the Debye equation for total polarization. Examples of dipole moments (in the gas phase) are water (1.854 D), ammonia (1.471 D), nitromethane (3.46 D), imidazole (3.8 D), toluene (0.375 D), and pyrimidine (2.334 D). Even symmetrical molecules will have a small, but measurable dipole moment, due to centrifugal distortion effects. Methane " for example, has a value of about 5.4 X 10 D. 

The electric properties of polymers are also related to their mechanical behavior. The dielectric constant and dielectric loss factor are analogous to the elastic compliance and mechanical loss factor. Electric resistivity is analogous to viscosity. Polar polymers, such as ionomers, possess permanent dipole moments. These polar materials are capable of storing... 

The electrical properties of materials are important for many of the higher technology applications. Measurements can be made using AC and/or DC. The electrical properties are dependent on voltage and frequency. Important electrical properties include dielectric loss, loss factor, dielectric constant, conductivity, relaxation time, induced dipole moment, electrical resistance, power loss, dissipation factor, and electrical breakdown. Electrical properties are related to polymer structure. Most organic polymers are nonconductors, but some are conductors. 

A number of other investigations of the electrical properties of lipid mono- and multilayers were published recently. It is obvious from studies of the conductivity of thin Langmuir films that the electrical properties of metal-organic layer-metal structures can be described by well known concepts from solid state physics, like Schottky injection of electrons from the metal into the lipid film (45, 46, 47). Measurements of dielectric losses in calcium stearate and behenate indicate the presence of movements of dipoles in the organic molecules, and loss peaks connected with the amorphous and crystalline parts of the layers were identified (48). 

Fuoss, R. M. Electrical properties of solids. VI. Dipole rotation in high polymers. J. Am. Chem. Soc. 63, 369—378 (1941). Note The dielectric data of Fig. 15 were taken from Document No. 1460, Amer. Documentation Inst. Library of Congress, Washington, D. C. 

Many important applications of polytetrafluoroethylene depend on its superb electrical properties tabulated in Table 3. These properties have been attributed to its highly symmetrical structure (Doban, Sperati, and Sandt). Complete fluorination of the carbon chain results in an exact balance of the electrical dipoles which is manifested in a very low dielectric constant and electrical loss factor. These two properties are virtually independent of the frequency from 60 to 109 cycles per second... 

Electrochemistry deals with charged particles that have both electrical and chemical properties. Since electrochemical interfaces are usually referred as electrified interfaces, it is clear that potential differences, charge densities, dipole moments, and electric currents occur at these interfaces. The electrical properties of systems containing charged species are very important for understanding how they behave at interfaces. Therefore, it is important to have a precise definition of the electrostatic potential of a phase [1-6]. Note that what really matters in electrochemical systems is not the value of the potential but its difference at a given interface, although it is illustrative to discuss its main properties. 

These effects are related to the electric properties of the reacting molecules, like their dipole moments and polarizability, as well as to solvent properties, like their dielectric constants and viscosity. 

The interactions between the molecule and the environment can lead to distortions in the electrical properties due to the susceptibility of the molecules and the properties of the host matrix. The refractive index of the matrix acts as a screening factor, modifying the optical spectra and interaction between charges or dipoles embedded within it. Local field effects change the interaction with an electromagnetic field and should be considered along with orientation factors in the dipolar interaction. 

Field forces due to the induced dipole moment of the field have been listed as evidence of nonthermal action of electric fields on biologic systems. However, the effects require fairly large field strengths, frequently above those that give rise to heating or stimulation of excitable tissues. The field forces also depend on the electric properties of the particle considered and its environment. 

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