Dielectric static

The size of the exciton is approximately 50 A in a material like silicon, whereas for an insulator the size would be much smaller for example, using our numbers above for silicon dioxide, one would obtain a radius of only 3 A or less. For excitons of this size, it becomes problematic to incorporate a static dielectric constant based on macroscopic crystalline values. 

Neumann M, Steinhauser O and Pawley G S 1984 Consistent calculation of the static and frequency-dependent dielectric constant in computer simulations Mol. Phys. 52 97-113... 

The dielectric constant is a property of a bulk material, not an individual molecule. It arises from the polarity of molecules (static dipole moment), and the polarizability and orientation of molecules in the bulk medium. Often, it is the relative permitivity 8, that is computed rather than the dielectric constant k, which is the constant of proportionality between the vacuum permitivity so and the relative permitivity. 

The dielectric constant (permittivity) tabulated is the relative dielectric constant, which is the ratio of the actual electric displacement to the electric field strength when an external field is applied to the substance, which is the ratio of the actual dielectric constant to the dielectric constant of a vacuum. The table gives the static dielectric constant e, measured in static fields or at relatively low frequencies where no relaxation effects occur. 

Finally, the dielectric properties of a nonpolar polymer are modified by inclusion of even small amounts of a polar comonomer. In coatings applications the presence of polar repeat units in an otherwise nonpolar polymer reduces the tendency for static buildup during manufacture, printing, and ultimate use. On the other hand, in dielectric applications this increases the power loss and must be kept to a minimum, even to the exclusion of polar initiator fragments. 

Values in parentheses are estimates. Values for band gaps decrease with increasing temperature, whereas values for the static dielectric constant and long wavelength refractive index increase with increasing temperature. 

Formal Theory A small neutral particle at equihbrium in a static elecdric field experiences a net force due to DEP that can be written as F = (p V)E, where p is the dipole moment vecdor and E is the external electric field. If the particle is a simple dielectric and is isotropically, linearly, and homogeneously polarizable, then the dipole moment can be written as p = ai E, where a is the (scalar) polarizability, V is the volume of the particle, and E is the external field. The force can then be written as ... 

For static electric properties, the bulk property of interest is the dielectric polarization P. The magnitude of P can be estimated from (for example) the Clausius-Mossotti relation... 

Other areas such as static electricity and its use and control were not discussed since they represent a different type of application (2). As new materials became available and the electrical art continued to develop, the uses for plastics in electrical applications has increase both in the basic application as a dielectric and in special applications using the special intrinsic properties of the plastics. 

Source Liu, C. et at, Electro-statically stricted polymers (ESSP), SPIE Conference on Electroactive Polymer Actuator and Devices, Newport Beach, California, March 1999, SPIE Vol. 3669,0277-786X/99 Kombluh, R. et at, Application of Dielectric Elastomer EAP Actuators, SPIE— the International Society for Optical Engineering, Bellingham, Washington, 2001, Chapter 16. 

The addition of salts modifies the composition of the layer of charges at the micellar interface of ionic surfactants, reducing the static dielectric constant of the system [129,130]. Moreover, addition of an electrolyte (NaCl or CaCli) to water-containing AOT-reversed micelles leads to a marked decrease in the maximal solubihty of water, in the viscosity, and in the electrical birefringence relaxation time [131],... 

FIGURE 6. (a) Values of for the solvated electron absorption bands plotted against the mole fraction DMSO for DMSO/H O mixtures, (b) Photon energy of the absorption band maxima for the solvated electron in DMSO/HjO mixtures plotted against the bulk static dielectric constant (25 °C) of the mixture. Non-linear axes showing dielectric constant and mole fraction for (a) and (b) respectively are given as top abscissae. Reproduced by permission of the authors from Reference 30. 

Azo-bridged ferrocene oligomers also show a marked dependence on the redox potentials and IT-band characteristics of the solvent, as is usual for class II mixed valence complexes 21,22). As for the conjugated ferrocene dimers, 2 and 241 the effects of solvents on the electron-exchange rates were analyzed on the basis of the Marcus-Hush theory, in which the t/max of the IT band depends on (l/Dop — 1 /Ds), where Dop and Ds are the solvent s optical and static dielectric constants, respectively (155-157). However, a detailed analysis of the solvent effect on z/max of the IT band of the azo-bridged ferrocene oligomers, 252,64+, and 642+, indicates that the i/max shift is dependent not only on the parameters in the Marcus-Hush theory but also on the nature of the solvent as donor or acceptor (92). 

---