Polarization dielectric constant and

The properties of HF reflect the strong hydrogen bonding that persists even in the vapor state. As a result of its high polarity and dielectric constant, liquid HF dissolves many ionic compounds. Some of the chemistry of HF as a nonaqueous solvent has been presented in Chapter 10. Properties of the hydrogen halides are summarized in Table 15.9. 

It is well established that acid-base equilibria and consequently pXa values can be subject to considerable variations in dependence of environment, namely, the polarity and dielectric constant of the solvent, solvation properties, and so on. This aspect is of particular significance in biological processes that occur at the interface of water and biomolecule aggregates. For example, variations in pXa values of amino acid side chains in proteins as well as local conditions in the... 

Other important physical chemical properties are polarity and dielectric constant. Water has a high dielectric constant (78.5 at STP), which would effectively mask ionic charges and lead to high solubility of ionic compounds. The dielectric constant of CO2 at 200 bar and 40°C is approximately 1.5, and CO2 is considered a very non polar solvent. As would be expected, polarity influences solubility for supercritical fluids. Carbon dioxide has a dipole moment of 0.0 Debye, while the value for NH3 is approximately 1.5. Therefore, C02 by itself is poorly suited for dissolving polar compounds. 

A brief investigation of the polymorphic form of each candidate salt shonld be nndertaken and as far as possible, the existence of polymorphism shonld be conhrmed or rnled ont. Polymorphs can be prodnced by simple recrystallization from a range of solvents, or solvent mixtnres, of different polarities and dielectric constants and their existence most easily conhrmed by a combination of hot stage microscopy (HSM), DSC or infrared or Raman spectroscopy and by powder X-ray techniqnes." ... 

Solvent strengths are also measured in terms of polarity, and dielectric constants are generally used to quantify relative strengths (Table 1). A high dielectric constant indicates a polar solvent with a strong power of elution, and a low dielectric constant indicates a nonpolar solvent with a lower ability to elute a component from a sorbent. This elution strength applies to normal phase adsorption chromatography. 

Table 9.3 displays the positions of the absorption peaks of porphyrin IX in solvents of different polarities and dielectric constants. The table shows that water induces a shift to the blue of bands I and II and a shift to the red of bands III and IV of the absorption spectrum compared to the spectrum obtained in other solvents. 

The following mechanism was put forward [31] to explain this autocatalysis (1) permeation by cosurfactant (amide) of the water-AOT-toluene interfacial regions as a result of partitioning equilibria with concomitant increase in polarity and dielectric constant in these regions (2) diffusion of swollen micelle to proximity of electrode surface (3) collision of swollen micelle with the electrode surface (de facto hemimicelle formation) or with a hemi-micelle on the electrode surface and diffusion of amide through the AOT interfacial region within the electron transfer distance of the electrode (4) irreversible oxidation of amide. 

R.H. Cole, "Induced Polarization and Dielectric Constant of Polar Liquids", Chem. Phys. 27 35 (1957)... 

II] Effect of Polarity and Dielectric Constant on Relative Strengths of Acids and Bases... 

The relative strengths of acids and bases is also affected by the polarity and dielectric constemt of the mediiun. Greater is the polarity and dielectric constant of the medium, the greater would be the acidic or basic strength of the species dissolved in that solvent. 

Possible polarization types include electronic (Figure 18.32a), ionic (Figure 18.32h), and orientation (Figure 18.32c) not all types need be present in a particular dielectric. For alternating electric fields, whether a specific polarization type contributes to the total polarization and dielectric constant depends on frequency each polarization mechanism ceases to function when the applied field frequency exceeds its relaxation frequency (Figure 18.34). 

In addition to the magnitude of the polarization and dielectric constant, other properties of importance which determine usefulness for a particular application are ease of polling, hysteresis losses, loop squareness, temperature and frequency dependence of the above ferroelectric properties, and aging effects. Aging refers to the stability of frequency as a function of time and is particularly important for filters. ... 

Clausius-Mosottf Jaw The molecular polarization (P) of a substance of molecular weight M, density d and dielectric constant O is ... 

The insulating properties of polyethylene compare favourably with those of any other dielectric material. As it is a non-polar material, properties such as power factor and dielectric constant are almost independent of temperature and frequency. Dielectric constant is linearly dependent on density and a reduction of density on heating leads to a small reduction in dielectric constant. Some typical data are given in Table 10.6. 

Most organic reactions are done in solution, and it is therefore important to recognize some of the ways in which solvent can affect the course and rates of reactions. Some of the more common solvents can be roughly classified as in Table 4.10 on the basis of their structure and dielectric constant. There are important differences between protic solvents—solvents fliat contain relatively mobile protons such as those bonded to oxygen, nitrogen, or sulfur—and aprotic solvents, in which all hydrogens are bound to carbon. Similarly, polar solvents, those fliat have high dielectric constants, have effects on reaction rates that are different from those of nonpolar solvent media. 

Fig. 5.21. The shock-induced polarization of polymers as studied under impact loading is shown. For the current pulse shown, time increases from left to right. The increase of current in time is due to finite strain and dielectric constant change. (See Graham [79G01]).

Correlations among solvent polarity scales, dielectric constant and dipole moment, and a means to reliable predictions of polarity scale values from current data. T. R. Griffiths and D. C. Pugh. Coord. Chem. Rev., 1979, 29,129-211 (130). 

As we have shown, the polarization force depends not only on the topography [through the f(R z) term] and dielectric constant e, but also on the local contact potential 4). As we shall see now, ac bias modulation and lock-in detection allow these contributions to be separated. 

The polarity of EVAs leads to an increase in loss factors and dielectric constants but the insulating properties allow their use for wire coating. For example, between 10% and 30% VA ... 

Solvent polarity was found to effect the rate of polymerization (Table I). For the three solvents studied, an essentially linear relationship (R=0.970) was observed between Rp and dielectric constant. 

Choquette et al. investigated the possibilities of using a series of substituted sulfamides as possible electrolyte solvents (Table 12). These compounds are polar but viscous liquids at ambient temperature, with viscosities and dielectric constants ranging between 3 and 5 mPa s and 30 and 60, respectively, depending on the alkyl substituents on amide nitrogens. The ion conductivities that could be achieved from the neat solutions of Lilm in these sulfamides are similar to that for BEG, that is, in the vicinity of 10 S cm Like BEG, it should be suitable as a polar cosolvent used in a mixed solvent system, though the less-than-satisfactory anodic stability of the sulfamide family might become a drawback that prevents their application as electrolyte solvents, because usually the polar components in an electrolyte system are responsible for the stabilization of the cathode material surface. As measured on a GC electrode, the oxidative decomposition of these compounds occurs around 4.3—4.6 V when 100 fik cm was used as the cutoff criterion, far below that for cyclic carbonate-based solvents. 

Figure 18. Correlations between the solubility of cmchonidme and the reported empirical polarity (A) and dielectric constants (B) of 48 solvents [66]. Those solvents are indicated by the numbers in the figures 1 cyclohexane 2 n-pentane 3 n-hexane 4 triethylamine 5 carbon tetrachloride 6 carbon disulfide 7 toluene 8 benzene 9 ethyl ether 10 trichloroethylene 11 1,4-dioxane 12 chlorobenzene 13 tetrahydrofuran 14 ethyl acetate 15 chloroform 16 cyclohexanone 17 dichloromethane 18 ethyl formate 19 nitrobenzene 20 acetone 21 N,N-drmethyl formamide 22 dimethyl sulfoxide 23 acetonitrile 24 propylene carbonate 25 dioxane (90 wt%)-water 26 2-butanol 27 2-propanol 28 acetone (90 wt%)-water 29 1-butanol 30 dioxane (70 wt%)-water 31 ethyl lactate 32 acetic acid 33 ethanol 34 acetone (70 wt%)-water 35 dioxane (50 wt%)-water 36 N-methylformamide 37 acetone (50 wt%)-water 38 ethanol (50 wt%)-water 39 methanol 40 ethanol (40 wt%-water) 41 formamide 42 dioxane (30 wt%)-water 43 ethanol (30 wt%)-water 44 acetone (30 wt%)-water 45 methanol (50 wt%)-water 46 ethanol (20 wt%)-water 47 ethanol (10 wt%)-water 48 water. [Reproduced by permission of the American Chemical Society from Ma, Z. Zaera, F. J. Phys. Chem. B 2005, 109, 406-414.]...

The terms polarizability constant and dielectric constant can be utilized interchangeably in the qualitative discussion of the magnitude of the dielectric constant. The k values obtained utilizing dc and low-frequency measurements are a summation of electronic E, atomic A, dipole P0, and interfacial /, polarizations. Only the contribution by electronic polarizations is evident at high frequencies. The variation of dielectric constant with frequency for a material having interfacial, dipole, atomic, and electronic polarization contributions is shown in Figure 6.1. 

We wanted to be able to correct measurements of dielectric loss (conductance) and dielectric constant of polymerizing styrene solutions for whatever contribution arose from the dead polystyrene present in the solutions. What better way to make polystyrene that was free of all catalyst fragments and polar groups than to irradiate pure, dry styrene Using the same exhaustive drying technique that we were developing for our a-methylstyrene studies, we prepared a batch of pure, dry styrene. This was then to be irradiated under such conditions that approximately 15% conversion to polymer would occur. 

The physicochemical properties of excipients used in pMDIs are different from most dosage forms and are a derivative of the propellant system that constitutes the bulk of the formulation. The transition from CFC-based formulations to HFA-based systems has been lengthened by the historically empirical formulation approach and the dissimilarity of the physicochemical properties of the replacement HFA propellants. Both HFA 134a and HFA 227 show an increased polarity, revealed in increased dipole moments and dielectric constant. The most significant practical change has therefore been a general change in the solvency properties. 

Figure 4.9 Effect of refractive index and dielectric constant of solvent on O—O transitions of a polar molecule.

The piezoelectricity of polymeric materials has in general a relax-ational nature and the piezoelectric stress constant e is a function of the frequency of the applied strain in a similar way to the elastic modulus and dielectric constant. The induced polarization has in-phase and out-of-phase components to the strain and the e-constant is expressed as a complex quantity, as in Eq. (32). 

The formation of solvates is association between unlike species. Solvation is more frequent between substances of high polarity than those of low polarity. This is illustrated by the decrease in the tendency to form solvates with decrease in dipole moment and dielectric constant (shown in parentheses) for N-methylacetamide (3.59 172), to water (1.84 78.4), to ethanol (1.70 24.6) to ammonia (1.48 78.4) to ethanol (1.70 24.6) to ammonia (1.48 J7.8) to me thylcy clohexane (0 2.02) for which few associations are known. 

The intrinsic UV fluorescence of proteins is dominated by the tryptophan indole rings. The absorption maximum is 280-290 nm with the fluorescence maximum ranging from 315-355 nm, depending on the local environment of the indole side-chains. Quantum yields range from 0.04 to 0.50 0.10 is a common value. As the local environment polarity or dielectric constant increases, the fluorescence maximum shifts up to 355 nm, such as for an indole ring in water or buffer. Trp moieties in highly hydro-phobic environments fluoresce at 315-320 nm. Thus the fluorescence emission maximum (and the quantum yield) provide indirect information as to the local environment of the Trp fluors. 

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