Lowering the Dielectric Constant

For low frequency electrical insulation appHcations, the dielectric constant of the insulation is ideaUy as low as possible (see Insulation, electrical). The lower the density of the ceUular polymer, the lower the dielectric constant and the better the electrical insulation. Dielectric strength is also reduced at... 

Time Delay and Velocity of Propagation. Time delay is direcdy proportional to the square root of the dielectric constant and describes the time that it takes for a signal to travel through a cable. The lower the dielectric constant, the less time required for a signal to travel through a cable. 

Further lowering the dielectric constants has been achieved by preparing highly fluorinated polyethers without any sulfone, ketone, or other polarizable groups.239 241 Typically, the /jara-lluorinc atoms on highly fluorinated aromatic compounds, such as hexafluorobenzene and decafluorobiphenyl, are activated and thus can go through aromatic nucleophilic substitution with HFBPA under typical reaction conditions (Scheme 6.31).217... 

Fluorinated Silicon Oxide. The introduction of fluorine in the ratio of 2 to 14 at.% lowers the dielectric constant, which is reported as low as 3.0. This is a major factor in the design of dielctric films. The CVD of these fluorinated compounds is accomplished by plasma-CVD and usually with Sip4 as a fluorine source. Also available are fluorinated compounds, such as fluorotriethoxysilane (FTES), l,2bis(methyldifluorosilyl)ethane, and 2,5disilahexane.P2]... 

The cosolvent will lower the dielectric constant of the mixed solvent, independent of the properties of the solute molecule. The ionization constant of acids will increase and that of bases will decrease (see Sections 3.3.3 and 3.3.4), the result of which is to increase the fraction of uncharged substance in... 

Due to the finite size of the ions and the solvent molecules, the solution shows considerable structure at the interface, which is not accounted for in the simple Gouy-Chapman theory. The occurrence of a decrease of C from the maximum near the pzc is caused by dielectric saturation, which lowers the dielectric constant and hence the capacity for high surface-charge densities. 

It follows from the above discussion (sections II. 5,6,7), that the thicker the organic ligand shell and the lower the dielectric constant of the... 

Fe solutions have been aerated at pH 7.2 in the presence of various minerals and rocks including quartz and basalt (Posey Dowty et al., 1986). The major product in all cases except that of quartz (goethite) was lepidocrocite. These authors also noted that lowering the dielectric constant of the solvent (by replacing water with a mixture of water and dioxane) promoted goethite over lepidocrocite. Poorly crystalline lepidocrocite was also the sole product when Fe was oxidized at pH 7 and RT in the presence of bacteria (Bacillus suhtilis Escherichia coli) (Chatellier et al. 2001) (see also chap. 17). 

Organic molecules in the solvent. The introduction of a water-miscible organic component lowers the dielectric constant of water. This has the net effect of increasing the attractive forces between groups of opposite charge and therefore of reducing the interactions between the water and the protein molecules consequently, the solubility of the protein will decrease. 

Addition of a water-miscible organic solvent tends to lower the dielectric constant e, which in turn enhances charge-dipole and dipole-dipole interactions, which again in turn reduces protein solubility and induces protein precipitation. The empirical correlation of Eq. (8.62) has been found very useful [S] is protein solubility, [S]0 is solubility at infinite e, and I( is a constant (K < 0) at constant I and T but does depend on the charge and shape of the protein. 

From the expression for q, it is clear that the lower the dielectric constant of the solvent, the larger is the magnitude of q. Hence, when one replaces water with a nonaqueous solvent, the likelihood of ion-pair formation inaeases because of the increasing q (assuming that a does not inaease in proportion to q). 

Slant of the mobile phases decreases. The dielectric constant is expected to influence the position of the equilibrium in ionic secondary chemical equilibria of acidic compounds [80-83], The solvent has the ability to disperse electrostatic charges via ion-dipole interactions, which is inversely proportional to the dielectric constant of the solvent composition. The lower the dielectric constant, the lower the ionization constant of the acid, Ka, and consequently greater Ka values are obtained. 

A number of eases of satisfactory agreement with theoretical requirements have been found in methyl alcohol solutions this is particularly the case for the chlorides and thiocyanates of the alkali metals. Other electrolytes, such as nitrates, tetralkyl-ammonium salts and salts of higher valence types, however, exhibit appreciable deviations. These discrepancies become more marked the lower the dielectric constant of the medium, especially if the latter is noii-hydroxylic in character. The conductance of potassium iodide has been determined in a number of solvents at 25 and the experimental and calculated slopes of the plots of A against Vc arc quoted in Table XXV,... 

The experimental data show that the deviations from the Onsager equation which may be attributed to incomplete dissociation occur more readily the smaller the ions, the higher their valence and the lower the dielectric constant of the medium. This generalization, as far as ionic size is concerned, appears at first sight not to hold for the salts of the alkali metals, for the deviations from the Onsager equation become more marked as the atomic weight of the metal increases owing to the effect... 

The lower the dielectric constant e of the solvent, the stronger the interionic interactions and, thus, the relaxation and electrophoretic effects. For the latter, solvent viscosity also plays a decisive role. When both the relaxation and the electrophoretic constants are known, the conductivity coefficient is obtained ... 

Lowering the dielectric constant of the medium by addition of solvents such as acetone or dioxan intensifies the colour. The colour s intensity doubles when the acetone concentration reaches 50 % by volume. Agreement with Beer s law is not observed. 

That work has been extended to provide even further reductions in the dielectric constants of aromatic condensation polyimides by physically incorporating selected diamic acid additives into low dielectric constant polyimide systems. The monomer selection for the synthesis of these additives was based on the results of the Langley structure-property studies on lowering the dielectric constant of polyimides.CL)... 

The ability of these additives to lower the dielectric constant appears limited as the dielectric constant of the base resin is lowered even further. Screening of the 6FDA-An, ODPA-An, 4-BDAF-PA and 3-BDAF-PA additives in 6FDA/3-BDAF did not result in any reduction in the dielectric constant of the base resin from its already... 

Two of the additives were also incorporated into a more conventional polyimide system, pyromellitic dianhydride (PMDA)/4,4 -ODA, to see if the diamic acid additives were effective in lowering the dielectric constant of a higher dielectric constant polyimide also. The evaluation was preliminary in that only two additives were screened at one concentration. As is shown in Table IV the dielectric constant was lowered, though not as significantly as in the BDSDA/4-BDAF system. 

The reaction medium, especially the pH, determines the constants for a given pair of reactants. To obtain an equilibrium that is shifted in favor of peptide product formation the ionization equilibrium must be manipulated. One efficient method is the addition of water-miscible organic solvents to the aqueous reaction mixture thereby lowering the dielectric constant of the medium, reducing the acidity of the carboxyl group, and to a lesser extent the basicity of the amino group of the nucleophilic amine component[100 1011 The use of biphasic systems (for a review... 

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