Anisotropy dielectric

It is evident that the sign of the dielectric anisotropy is not fixed by the form of this expression and that it depends on the magnitude of Aa as well as on the... 

From a practical perspective a high dielectric anisotropy leads to a low operating voltage according to... 

Note 2 The basic electric parameters determining EHD instabilities are the dielectric anisotropy, Af, and the anisotropy of the (ionic) conductivity, A a. 

Note 1 The nematic liquid crystal must have a negative dielectric anisotropy (Af < 0), and a positive anisotropy (Aa > 0). The optical texture corresponding to the flow pattern consists of a set of regularly spaced, black and white stripes perpendicular to the initial direction of the director. These stripes are caused by the periodicity of the change in the refractive index for the extraordinary ray due to variations in the director orientation. 

Leslie coefficients, Leslie-Ericksen coefficients dielectric anisotropy... 

The dielectric anisotropy of long-chain fatty acid monolayers was analyzed. These fatty acids were considered as being oriented in a cylinder cavity with length (L) diameter (D). Considering each bond in these molecules as a polarization ellipsoid with axial symmetry about the -C-C- bonds, the mean polarizibtlity of the bonds was calculated. 

In the case of those LC materials which exhibit negative dielectric anisotropy, cells can be constracted which align vertically and twist on applying a field, exactly the converse to the twisted nematic effect from positive anisotropic LCs. Cells of this type are of interest because they can form a superior black state. 

A new class of liquid crystals with strongly negative dielectric anisotropy was explored by employing the ambivalent characteristics of the 1,3-dioxane moiety <2006EJ04819> due to both the polarity of 1,3-dioxane and axial fluorination, compounds 238-240 proved to have very useful mesogenic and electrooptical properties. 

Secondary ferroics. SrXi03 (which is an incipient ferroelectric) and NaNb03 (which is an antiferroelectric) may be considered to be ferrobielectric. Xhe dielectric anisotropy in antiferroelectric domains can give rise to high values of induced polarization that are orientationally different in different domains. Xhus, they give rise to domain rearrangement under applied fields. Quartz is a classic example of... 

Dynamic scattering displays, which are the first generation LCDs, make use of a nematic LC with a negative dielectric anisotropy (As = — <0) doped with an... 

There has been an increasing interest in liquid crystals containing fluorine atoms because fluorination produces important changes in the melting temperatures, viscosity, birefringence, dielectric anisotropy and mesophase stability. This why structure-mesomorphism relationship studies were carried out in mono- and... 

It has been shown 65,68) that the threshold voltage is a function of the dielectric anisotropy Ae and the elastic constants of splay (ku), twist (k22) and bend (k33) deformation of the nematic phase (Fig. 17) ... 

The presence of these groups ensured a large value of the parallel component of the dipole moment in the side chain direction and a positive dielectric anisotropy of these polymers. 

Their measurements revealed no significant change of the dielectric anisotropy at the same reduced temperatures (TIso/N — T), which our group was able to confirm in related experiments using mixtures of 5CB doped with hexanethiol-capped gold nanoparticles [298]. 

Figure 2.30 Permittivity of two nematics with opposite dielectric anisotropy, as a function of temperature [ 1,2], In (a) the square of the refractive index (A =589 nm) is also shown [3],...

Figure 2.31 Electrostatic free energy for a dipole p = 5.65 D in a spherical cavity of radius a=5. 5 A in a uniaxial dielectric, as a function of the dielectric anisotropy Ae. The average permittivity is (a) < e > = 11 and (b) < e > = 9.5. Solid and dashed lines refer to the dipole parallel and perpendicular to the director, respectively.

Recently, the surface tensor model has been used together with the dielectric continuum model to calculate the orientational order parameters of solutes in nematic solvents [8,9,27], Figure 2.32 shows the theoretical results for anthracene and anthraquinone in nematic solvents with different dielectric anisotropy. Considering only the surface tensor contribution, positive Szz and Sxx and negative are obtained, with Szz > Sxx > Syy. This corresponds to what could be expected on the basis of the molecular shape the long axis (z) is preferentially aligned with the director, and the normal to the... 

Figure 2.32 Order parameters calculated for (a) anthracene and (b) anthraquinone dissolved in nematics with different dielectric anisotropy [9]. For the case Ae > 0, the results obtained in the absence of induction effects are also shown (dotted line). The temperature dependence of the dielectric anisotropy is taken into account, with the values eNI = 10.2, AeN/ = 8 and eNI = 5.2, AeN/ = —0.5 for the two cases at the nematic-isotropic transition. Atomic charges in absolute value greater than 0.1 are shown (in e units). The y axis is perpendicular to the molecular plane.

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