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Liquid crystal director

A typical experimental apparatus for studying photorefractivity in liquid crystals is illustrated in Fig. 2. Two coherent laser beams from an Ar+ laser are crossed in the sample, with a total of 5 mW of p-polarized output at 514 nm. The beams are unfocused and have a 1/e diameter of 2.5 mm. The liquid crystal composite is sandwiched between two ITO coated glass slides that are coated with octadecyl-silyl groups to induce the liquid crystal director to align perpendicular to the face of the glass slides, that is, homeotropic alignment [43], The cell thickness is determined by a Teflon spacer that is 12 to 100 p,m thick. A small electric field... [Pg.322]

MeOAn-ANI-3 NI in the nematic liquid crystal mixture E-7 (Merck) at two orientations of the liquid crystal director, L, taken 700 ns after a 420 nm laser pulse at 150 K. The narrow signal is an expansion of the radical pair signal, (b) Numerical differentiation of the B L L spectrum. [Pg.16]

The application of an electric field between the electrodes results in a realignment of the nematic liquid crystal mixture and the dichroic dye molecules parallel to the electric field resulting in a lower optical density (absorption) and, theoretically, the disappearance of colour assuming an ideal order parameter (S = 1) of the nematic liquid crystal director and the dye molecules. A residual absorption in this state gives rise to a display with a strongly coloured background and weakly coloured information. [Pg.111]

In microscale models the explicit chain nature has generally been integrated out completely. Polymers are often described by variants of models, which were primarily developed for small molecular weight materials. Examples include the Avrami model of crystallization,- and the director model for liquid crystal polymer texture. Polymeric characteristics appear via the values of certain constants, i.e. different Frank elastic constant for liquid crystal polymers rather than via explicit chain simulations. While models such as the liquid crystal director model are based on continuum theory, they typically capture spatiotemporal interactions, which demand modelling on a very fine scale to capture the essential effects. It is not always clearly defined over which range of scales this approach can be applied. [Pg.245]

Figure 3.89. Normalized TP fluorescence intensity of polymer dispersed liquid crystals as a function of the polarization angle of the reading beam, which is defined as the angle between the writing and reading polarization states. Inset top Schematic alignment of liquid crystal directors in exposed (dots) and unexposed regions. Inset bottom Two fluorescing data bits obtained by irradiation at a polarization angle of 90°. (From Ref. [248] with permission of the American Institute of Physics.)... Figure 3.89. Normalized TP fluorescence intensity of polymer dispersed liquid crystals as a function of the polarization angle of the reading beam, which is defined as the angle between the writing and reading polarization states. Inset top Schematic alignment of liquid crystal directors in exposed (dots) and unexposed regions. Inset bottom Two fluorescing data bits obtained by irradiation at a polarization angle of 90°. (From Ref. [248] with permission of the American Institute of Physics.)...
The TN cell is schematically shown in Figure 1.19. The liquid crystal sandwiched between two indium-tin-oxide (ITO) coated glass plates is about a few microns in thickness. The liquid crystal molecules on the top and bottom plates are homogeneously aligned and twisted by an angle of 7t/2. The liquid crystal molecules have a positive dielectric anisotropy sa > 0 so that an electric field will rotate the liquid crystal director up. The threshold voltage is given by... [Pg.34]

There is an orientational order in the liquid crystals which are anisotropic fluids. The director field n(r) or its components n affect the hydrodynamic behavior, so that is dependent on the distortion of the director field as well. For convenience, we designate a vector N for the angular velocity of liquid crystal directors with respect to the background fluid,... [Pg.301]

In equations (5)-(8), i is the molecule s moment of Inertia, v the flow velocity, K is the appropriate elastic constant, e the dielectric anisotropy, 8 is the angle between the optical field and the nematic liquid crystal director axis y the viscosity coefficient, the tensorial order parameter (for isotropic phase), the optical electric field, T the nematic-isotropic phase transition temperature, S the order parameter (for liquid-crystal phase), the thermal conductivity, a the absorption constant, pj the density, C the specific heat, B the bulk modulus, v, the velocity of sound, y the electrostrictive coefficient. Table 1 summarizes these optical nonlinearities, their magnitudes and typical relaxation time constants. Also included in Table 1 is the extraordinary large optical nonlinearity we recently observed in excited dye-molecules doped liquid... [Pg.121]

The surface tension determines capillary effects, wetting phenomena and a shape of liquid drops, in particular, the spherical shape of small radius drops when the gravity is not essential. The corresponding excess pressure in a drop of radius p is Ap = 2a/p (Laplace-Young formula). Small drops of the nematic phase are, strictly speaking, not spherical due to anisotropy of the surface tension but practically they may be considered spherical. The surface tension of both a liquid crystal and a solid substrate determines orientation of the liquid crystal director on the substrate. [Pg.258]

The tradeoff between angular viewing dependence and N is shown explicitly in Fig. 2 where measured contrast ratio is plotted as a function of the angle of incidence 0 in the principal viewing plane for a typical TN-LCD with E-7 biphenyl liquid crystal mixture between crossed polarizers. The principal viewing plane is defined by the sample normal and the liquid crystal director midway between the cell electrodes. Contrast ratio is defined as the ratio of cell transmission I with Vjjg applied to transmission with V3 applied. [Pg.82]

In nematic phase, the liquid crystal director it is uniform in space in the ground state. In reality, the liquid crystal director it may vary spatially because of confinements or external fields. This spatial variation of the director, called the deformation of the direetor, eosts energy. When the variation occurs over a distance much larger than the moleeular size, the orientational order parameter does not change, and the deformation ean be deseribed by a continuum theory in analogue to the classic elastic theory of a solid. The elastie energy is proportional to the square of the spatial variation rate. [Pg.21]

Figure 1.9 The three possible deformations of the liquid crystal director (a) splay, (b) twist, and (c) bend. Figure 1.9 The three possible deformations of the liquid crystal director (a) splay, (b) twist, and (c) bend.
Smectic liquid crystals possess partial positional orders besides the orientational order exhibited in nematic and cholesteric liquid crystals. Here we only consider the simplest case smectic-A. The elastic energy of the deformation of the liquid crystal director in smectic-A is the same as in nematic. In addition, the dilatation (compression) of the smectic layer also costs energy, which is given by [23]... [Pg.26]

Figure 1.12 Schematic diagram showing the deformation of the liquid crystal director and the smectic layer in the smectic-A liquid crystal. Figure 1.12 Schematic diagram showing the deformation of the liquid crystal director and the smectic layer in the smectic-A liquid crystal.
Liquid crystals are anisotropic dielectric and diamagnetic media [1,25], Their resistivities are very high ( 10 °Q cm). Dipole moments are induced in them by external fields. They have different dielectric permittivities and magnetic susceptibilities along the directions parallel to and perpendicular to the liquid crystal director. [Pg.27]

E as well as the angles between E and the long molecular axis a and the liquid crystal director n. They are related to each other by... [Pg.31]

Next we need to find the form of K in the lab frame xyz with the z axis parallel to the liquid crystal director n. Because of the axial symmetry around a, we only need to consider the transformation of the matrix between the two frames as shown in Figure 1.16. The frame is... [Pg.31]

When the liquid crystal director n is aligned along the direction specified by the polar angle G and azimuthal angle (p, the anisotropic part of the surface energy - referred to as the anchoring energy function - of the liquid crystal isfs=fs G,(p). When G = Gg and

[Pg.38]

Figure 1.18 Schematic diagram showing the easy direction of the surface anchoring and the deviation of the liquid crystal director. Figure 1.18 Schematic diagram showing the easy direction of the surface anchoring and the deviation of the liquid crystal director.

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See also in sourсe #XX -- [ Pg.63 , Pg.65 , Pg.67 ]

See also in sourсe #XX -- [ Pg.771 ]




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