Dielectric constant, factors affecting

Moderate insulators with lower resistivity and higher dielectric constant and power factor affected further by the conditions of the test. These materials are often referred to as polar polymers. 

Very recently we8 reported on a class of processable heavily fluorinated acrylic resins that exhibit dielectric constants as low as 2.10, very close to the minimum known values. In this chapter we report on the preparation of a series of processable heavily fluorinated acrylic and methacrylic homo- and copolymers that exhibit dielectric constants as low as 2.06, and the factors that affect the reduction of dielectric constant from structure-property relationships is elucidated.9... 

The principal factors affecting solvent-ion interactions can be classified as ion-dipole, Lewis acid-base, hydrogen-bonding, solvent structural, and steric. The solvent obviously plays a major part in these interactions. Therefore, to interpret trends in conductance data, bulk solvent properties such as viscosity and dielectric constant should be considered. Table 1 lists selected physical properties for a number of organic solvents. 

The initiation step could also be positively affected by the above-mentioned transport properties, as the efficiency factor f assumes higher values with respect to conventional liquid solvents due to the diminished solvent cage effect One further advantage is constituted by the tunability of the compressibility-dependent properties such as density, dielectric constant, heat capacity, and viscosity, all of which offer additional possibilities to modify the performances of the polymerization process. This aspect could be particularly relevant in the case of copolymerization reactions, where the reactivity ratios of the two monomers, and ultimately the final composition of the copolymer, could be controlled by modifying the pressure of the reaction system. 

Let us examine the structure of expression (16). The influence of the dielectric medium constant e0 affects the factor aroused from the long-range Coulomb s field of the donor and acceptor charges, (iexponential factor in g(rDA) is not yet examined. Note, the expression — (l/r )exp —differs from the Green s function of a free electron Go( D,r E) by the numeric factor l/2n only (see formula (6)). Therefore it will be considered that the influence of the medium on Green s function of a free electron does not interact with the donor and the acceptor. 

Thus, the medium dielectric constant e is varied by 40%, while Pekar s factor y is changed by 14% in the whole range of available viscosities. The change in e affects the Coulomb interactions in the [Ru3+ MV+] pair, while the change in y affects the outer-sphere reorganization energy. The viscosity dependence of both e and y is accurately interpolated by the two-exponential model function... 

The loss factor will vary in some degree with the formulation of the material and (as the product of the dielectric constant and the power factor), will be affected by other parameters such as the frequency applied. However, in practice variations for reasons such as these are not significant. 

Methyl silicone rubber also shares the excellent electrical properties of the resins and oil. A molded sample with silica filler had a dielectric constant of 3.0 at room temperature over a range of 60 to 1010 cycles. The loss factor remains at 0.004 from 60 to 107 cycles and then rises rapidly to 0.037 at 109 cycles and 0.055 at 1010 cycles. At 102° C. the values remain the same except for a small decrease in dielectric constant (caused by a decrease in density) and a slight indication of enhanced d-c conductivity. The rubber does not seem to be affected by ozone. 

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