Dielectric permittivity, pressure effects

It should be mentioned that even in the absence of dipolar, polarizable, or ionic reaction partners, high electric fields may cause shifts in chemical distributions. Such a field effect requires, however, that the solvent phase has a finite temperature coefficient of the dielectric permittivity or a finite coefficient of electrostriction an additional condition is that the chemical reactions proceed with a finite reaction enthalpy (AH) or a finite partial volume change (A V). Electric field induced temperature and pressure effects of this type are usually very small they may, however, gain importance for isochoric reactions in the membrane phase. 

Pressure influences the dielectric permittivity of liquid crystalline phases considerably. For some LCs that form antiparallel dimers, the observation of a small maximum in s(T) at 1 atm above the clearing temperature is well established. In recent high-pressure investigations a similar effect was found, that is, a maximum in e(p) at T = const in the isotropic phase in the neighbourhood of the NI transition. 

Perhaps the most common way to calculate solvent effects is to use a continuum solvent model. Here, the molecular structure of the solvent is ignored and the solvent is modeled as a continuous dielectric of infinite extent that surrounds a cavity containing the solute molecule M. (A dielectric is a nonconductor of electricity.) The continuous dielectric is characterized by its dielectric constant (also called relative permittivity) e whose value is the experimental dielectric constant of the solvent at the temperature and pressure of the solution. The solute molecule can be treated classically as a collection of charges that interacts with the dielectric or it can be treated quantum mechanically. In a quantum-mechanical treatment, the interaction between a solute... 

The electrostriction caused by an ion has been estimated on the basis of the electrostatic effects the very high electric held of an ion has on the water surrounding it. This field exerts a large pressure on the water and sharply decreases its permittivity, down to dielectric saturation. A stepwise shell-by-shell calculation (Marcus and Hefter 1999) yields the desired quantity ... 

In Fig. 2, the relative permittivities (static dielectric numbers) e of carbon dioxide [23], argon [24], and liquid pentane [25] are plotted against pressure p up to 200 MPa. Even at the highest pressures corresponding to liquid-like densities, e (CO2) is smaller than 1.8, and thus nearly equal to that of a liquid alkane (such as pentane). Since CO2 molecules do not have any permanent electrical dipole moment, the polarization is more or less restricted to the contributions of the electrons and the nuclei. Therefore, typical solvation effects are normally less important, and the intermolecular interactions are predominantly of van-der-Waals type with some higher electrostatic such as quadrupolar interactions. 

Results showed that the textile-based sensor behavior is close to the expected one and already at this stage the stmcture might be used to indicate the presence of a pressure. The deviation was mainly due to the lateral movement of the conductive layers. As the distance decreases the rigidity of the spacer stmcture produces a shear force, which makes the conductive layers move laterally so that the overlapping area is no longer constant. Future work should aim to resolve the unwanted lateral motion of the conductive layers as well as to make a precise model of the partially filled capacitor in order to predict the effective permittivity of the dielectric. If fliese issues are taken care of the stmcture will also be suitable for making absolute measurements of either distance or pressure. 

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