Small dielectric constant

The mechanism of the cycloaddition of phenyl azide to norbornene has been shown to involve a concerted mechanism with a charge imbalance in the transition state (199). In a similar manner the cycloaddition of phenyl azide to enamines apparently proceeds by a concerted mechanism (194, 194a). This is shown by a rather large negative entropy of activation (—36 entropy units for l-(N-morpholino)cyclopentene in benzene solvent at 25°C), indicative of a highly ordered transition state. Varying solvents from those of small dielectric constants to those of large dielectric constants has... 

Because of the likely high ionic concentration and the small dielectric constant of the oxide, the diffuse layer thickness is expected to be small, and hence this space charge is limited to a few nanometers. 

The experimental result obtained was explained by the formation of ion pairs between the charges of a network and counter ions. The theoretical analysis of this problem has shown that the degree of ion pairs formation very strongly (exponentially) depends on e (cf. Sect. 2.2). Thus, if the precipitant has a small dielectric constant e (e.g. dioxane) the degree of dissociation of ion pairs is sufficiently small and this fact leads to the decrease of the osmotic pressure of counter ions which defines the swelling of the gel and the point of the transition in the collapsed state. As a result, in this case the degree of swelling of the gel near the transition point is less pronounced than for other solvents and only a relatively small amount of the precipitant is required to reach this point. In... 

As mentioned earlier, at 500° C and 34.5 MPa supercritical water has a small dielectric constant, a very low ion product, and behaves as a high temperature gas. These properties would be expected to minimize the role of heterolysis in the dehydration chemistry. As shown in Table 1, the conversion of ethanol to ethylene at 500° C is small, even in the presence of 0.01M sulfuric acid catalyst. The appearance of the byproducts CO, C02) CH i+ and C2H6 points to the onset of nonselective, free radical reactions in the decomposition chemistry, as would be expected in the high temperature gas phase thermolysis of ethanol. 

For pro tic solvents with larger dielectric constants and stronger basicity, the La and 1Lb states are inverted and relaxation from xLb to xLa takes places but there is no proton transfer to the solvent. The fluorescence is then due to the 1LB state with a small Stokes shift. The intermediate sized water clusters (n = 10-20) belong in this category. The clusters with methanol for any size n < 10 (due to a weak basicity or a small dielectric constant) follow this mechanism. From the evaluated proton affinities (see Figure 4-16), it can be seen that for n k 10 molecules of methanol (PA 243 kcal mol-1 which corresponds to the limit for proton transfer evidence in 1-naphthol complexes with piperidine or ammonia), a proton transfer should be observed. The absence of such a transfer can be related to a cluster structure effect. 

This hquid (b.p. 21 ) has a very low conductance and small dielectric constant (2.4). Its ionisation (Gray, 1957) is... 

Unfortunately, the discussion above proves to be rather academic, since (3.36) has a serious practical problem. The relationship between e and g is such that for e> 10 (/x >l for dipolar hard spheres), small uncertainties in g lead to very large errors in e. Thus except for systems with relatively small dielectric constants, (3.36) is not very useful. 

MHPOBC was first reported as a new FLC in the Japan domestic liquid crystal meeting in 1985 by Inukai et al. [2]. In the First International FLC Conference in 1987, two groups pointed out unusual behavior in this com-poimd. Hiji et al. [3] reported a third stable state exhibiting a dark view between crossed polarizers when one of the polarizers is parallel to the smectic layer. Furukawa et al. [4] reported a very small dielectric constant and a threshold behavior in the electro-optic response in the lower temperature region of SmC, suggesting a new phase, SmY. ... 

If f,v, is not very large (less than 10 for most small dielectric constant materials ), s always larger than (c , p-2), thus p will increase as A... 

In the other cases, it is essential to examine if the electrostatic factor is important, for instance in weakly polar solvents that have small dielectric constants (e low) and when the reacting species are small (d low). 

The dielectric constant refers to polarization of the medium (i.e., both the electronic polarization and the physical reorientation about bonds or molecules) in response to external sources of electric field. Polarization of the electron cloud in a molecule happens quickly, so this is called the high frequency component of the dielectric constant and is represented with a small dielectric constant, say 2. The reorientation of side chains, other changes in conformation, and movement of molecules, which take more time, is the low frequency component of the dielectric response and is accorded a higher dielectric con-... 

Pyroelectric polymers have additional features as pyroelectric devices, such as large surface area, thin films, low thermal diffusion, small dielectric constant, flexible for conformity to curved surface and low cost, though their pyroelectric coefficients are generally smaller than other materials. Pyroelectric devices using polymer elements with these features may have a large number of applications which ate not necessarily restricted to IR radiation detector. 

Materials with a small dielectric constant, such as ferroelectric polymers, are best suited to large-area elements, and vice versa. 

Here, I would like to go off on a tangent about the 1st international ferroelectric liquid crystal conference. One of the most important moments for the discovery of antiferroelectrie liquid crystal was the presentation by Kenji Furukawa (Chisso Corp.) on this conference [47]. The designated SmY phase exists at the low-temperature side of the SmC phase of MHPOBC it has an abnormally small dielectric constant compared to the ferroelectric phase, indicating a threshold during the direct current switching by an electric field. Thus, experimental facts pointed to an antiferroelectrie phase rather than a ferroelectric phase as early as 1987. 

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