Director dynamics

In [11], the simplified models of director dynamics in two geometries were examined. One was the director dynamics induced by obliquely incident, linearly polarized light. The simple model of this geometry [23] (see section... 

Another simple model investigated in [11] is a model of the director dynamics induced by circularly polarized light using three variables. The stability of the basic state and the uniformly processing state above the OFT was investigated, and it was found that both of these states remain stable against any... 

Gu, D., and Jamieson, A. M., Rheological characterization of director dynamics in a nematic monodomain containing mesogenic polymers of differing architectures. Macromolecules, 27, 337-347 (1994a). 

The equilibrium configuration in a liquid crystal sample is strongly influenced by the sample boundaries. The confining surfaces can induce order, disorder, or can align liquid crystal molecules in a given direction. Surface interactions not only have influence on the static properties of a confined liquid crystal, but can also have a strong effect on the director dynamics. By studying temporal fluctuations of the director field in confined samples, information about the surface-liquid crystal interaction can be obtained. 

Further studies have tackled the director dynamics [8] and the geometrically caused frustration [52,53], Theoretical studies of the highly frustrated sub-micron hybrid systems where the order becomes biaxial [10,54,55] have recently been delhonstrated also by MC simulations [16] but experimental evidence is still lacking. 

As a consequence the limit ca — 0 is not smooth, since in the DC case (w = 0) the time average of both and Uy are finite. A closer look at the director dynamics in the AC case shows that non-zero values of nz t) and ny t) appear only during a very small fraction of the period T = Iw. 

So far we have discussed EC instabilities driven by a sinusoidal AC voltage. When the AC driving voltage U t) with period T is asymmetric , i.e. U(t -h T/2) —U t), besides the conductive and the dielectric symmetries there is a subharmonic pattern where the director dynamics is 2T-periodic in time. The effect of flexopolarization on standard and non-standard EC for an asymmetric driving voltage has been analysed. One recovers in principle the scenarios with symmetric driving described... 

Using constraint director dynamics, McWhirter and Patey [206] also determine the shear and twist viscosities describing the coupling between the pressure and shear rate tensors and the Miesowicz viscosities (linear combinations of the former) and show that the latter are qualitatively similar to those of a ferroelectric tetragonal 1 lattice in accord with the fact that the short-range spatial correlations in the ferroelectric liquid state are similar to those of the tetragonal lattice structure [102]. 

R. Mahmood, I. Khan, C. Gooden, A. Baldwin, D. L. Johnson, M. E. Neubert, Light-scattering study of director dynamics above the nematic-smectic-A transition, Phys. Rev. A 1985, 32, 1286. 

To test the basic feature of Eq. (10-22), namely, the competition between the instantaneous and memory contributions to the total torque, one can trace the director dynamics by measuring the optical phase retardation of the cell filled with MLC2048. The dielectric torque is maximized by choosing a high value of the angle between the director and the normal to the bounding plates, 9q 45° [11, 12], The cell thickness was 10 xm. 

The switching memory effect is a reflection of the fact that the electric displacement, being the function of both the applied field and the material s properties, needs some finite time to adjust to the value of the electric field. The widely accepted model of the instantaneous relationship between the electric displacement and the electric field in the NLC is invalid when the characteristic times of the director dynamics are close to the relaxation times for molecular permanent dipoles. This time scale is typically in the submillisecond range which is of great interest for modem fast-switching devices. The electric displacement (as well as the dielectric torque density) becomes a function of the static dielectric properties of the NLC, the present and past electric field, and the present and past director. We discussed the recently proposed theory and experimental verification of the phenomenon [11]. The model in Ref [11] should be applicable to dynamic reorientation of other LC phases in the appropriate range of times/frequencies. In the case of ferroelectric LCs, the theory should be supplemented by the consideration of spontaneous electric polarization. A similar approach should be also... 

The amplitude of the scattered field Eg varies with time due to the fluctuations in the director orientation and hence the dielectric tensor. Therefore, a very convenient way to observe the director dynamics is to study the dynamics of the scattered light, i.e. to use dynamic light scattering for measuring the autocorrelation function of the scattered light. The normalised intensity autocorrelation function (q, tf) is defined as [11]... 

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