Dielectric enrichment

Dielectric enrichment, 23 109 Dielectric materials, polyimide, 20 278 in multilayer capacitors, 11 102 Dielectric measurements, 10 17, 425-426 Dielectric overlayers, in compound... 

A simple model of a solute molecule of dipole moment fj, and molecular radius a, surrounded by a mixture of two solvents N and P of polarity functions f(DN), f Df) and bulk mole fractions N and xv yields an equation for dielectric enrichment as the local mole fractions change to j>N, yP the equilibrium condition is... 

P. Suppan, Time-resolved luminescence spectra of dipolar excited molecules in liquid and solid mixtures - dynamics of dielectric enrichment and microscopic motions, Faraday Discuss., (1988) 173-84 L. R. Martins, A. Tamashiro, D. Laria and M. S. Skaf, Solvation dynamics of coumarin 153 in dimethylsulfoxide-water mixtures Molecular dynamics simulations, J. Chem. Phys., 118 (2003) 5955-63 B. M. Luther, J. R. Kimmel and N. E. Levinger, Dynamics of polar solvation in acetonitrile-benzene binary mixtures Role of dipolar and quadrupolar contributions to solvation, J. Chem. Phys., 116 (2002) 3370-77. 

Kauffman and coworkers118 119 tried to fit the solvatochromic shifts of l-(9-anthryl)-3-(4-/V,/V-dimcthylanilino)propanc (83), relative to the hydrocarbon homomorph with the dimethylamino group replaced by H, to the dielectric non-ideality of solvent mixtures involving hexane with ethanol, tetrahydrofuran and dichloromethane. The shifts were not linear with the mole fraction of the polar component, and Suppan s theory of dielectric enrichment was applied to the data. It was found that the dielectric enrichment that can be calculated from the relative permittivities of the components and of the mixtures is not sufficient to account for the observed solvatochromic shifts, but that preferential solvation of the probe by the polar component is superimposed on this dielectric effect. Earlier,... 

Boggetti H, Anunziata ID, Cattana R, SUber 11 (1994) Solvatochromic study on nitroanihnes. Preferential solvation vs dielectric enrichment in binary solvent mixtures. Spectrochim Acta A Mol Spectrosc 50 719-726... 

Dielectric relaxation measurements of polyethylene grafted with acrylic acid(AA), 2-hydroxyethyl methacrylate (HEMA) and their binary mixture were carried out in a trial to explore the molecular dynamics of the grafted samples [125]. Such measurements provide information about their molecular packing and interaction. It was possible to predict that the binary mixture used yields a random copolymer PE—g—P(AA/HEMA), which is greatly enriched with HEMA. This method of characterization is very interesting and is going to be developed in different polymer/monomer systems. 

Of all the elements, fluorine is the most reactive and the most electronegative (a measure of tendency to acquire electrons). In its chemically combined form, it always has an oxidation number of -1. Fluorine has numerous industrial uses, such as the manufacture of UF6, a gas used to enrich uranium in its fissionable isotope, uranium-235. Fluorine is used to manufacture uranium hexafluoride, SF6, a dielectric material contained in some electrical and electronic apparatus. A number of organic compounds contain fluorine, particularly the chlorofluorocarbons used as refrigerants and organofluorine polymers, such as DuPont s Teflon. 

The inclusion of solvent effects enriches this kind of analysis. In fact, by tuning the value of the solvent dielectric permittivity s, which is included in the expression... 

The multilayered character of acetonitrile adsorption creates a pseudo-stationary phase of significant volume on the surface, which acts as a suitable phase for the ion accumulation. In the low organic concentration region (from 0 to 20 v/v% of acetonitrile), studied ions show significant deviation from the ideal retention behavior (decrease in ion retention with increase in acetonitrile composition) due to the formation of the acetonitrile layer, and significant adsorption of the chaotropic anions was observed. This creates an electrostatic potential on the surface in which there is an adsorbed acetonitrile layer, which provides an additional retentive force for the enhancement of the retention of protonated basic analytes. When the dielectric constant is lower than 42 [167], this favors the probability of ion pair formation in this organic enriched layer on top of the bonded phase. 

The model conceptualises the solution of (noble) gases on the microscopic level as cavities built by water molecules that trap individual (noble) gas atoms. The attracting forces between water and host increase with the atomic radius and the dielectric constant of the (noble) gas. In consequence, the intermolecular forces increase with molecular mass. This explains why the ratios of elemental noble gas concentrations in water at atmospheric equilibrium are enriched with respect to the atmospheric abundance in favor of the heavier noble gases. 

A plot of ee and e as a function of pressure (Figure 4.7-7(a)) shows the reverse relationship between the polarity of the medium and die enrichment of the (/ ,5)-enantiomer. The increase in asymmetric induction with decreasing pressure is fully in line with its increase with decreasing e in liquid solvents, as demonstrated for the enantiomeric ratio in Figure 4.7-7(b). This new result demonstrates the possibility of dielectric tuning of catalytic reactions in SCFs. 

However, in most cases a limited miscibility (depending on Ni and k) (see Eq. 12.52) is observed leading to two phases enriched in mie compmient which can be described by a concentration Q. In principle the cmicepts developed in Sect. 12.4.2 can be employed to model the dielectric properties of each phase. In principle by analyzing the frequency position of the a-relaxati(Mi and its dielectric strength, the unknown concentration of each component can be estimated assuming appropriate mixing rules. In practical work this can be difficult. Of special interest is again the case where one component is dielectrically invisible as also discussed in Sect. 12.4.2. 

Figure 4 shows typical variations of the dielectric relaxation with water content as recorded along a line stretched across I( /o) and directed towards the 100% water vertex of the pseudo-ternary phase diagram, that is for systems characterized with a fixed ratio of combined surface-active agents to hexadecane and enriched gradually with water. While dielectric relaxation phenomena are hardly detectable at low water contents, systems characterized with higher water contents exhibit striking dielectric relaxations, the dielectric increment (e - e ) increasing drastically as p approaches the critical value corresponding to the transparent-to-turbid transition. The increase in (G - e ) results from the drastic increase in the low frequency permittivity whose variations with p are plotted in Figure 5a. While at low water contents, increases slowly and almost linearly with p, it displays a divergent behavior in the vicinity of the border line F. Simi-...

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