Oblique alignment

Freely suspended films provide a perfect homeotropic alignment of smectic LCs since the layers always orient parallel to the LC/air interface.33 The director structure in such films can then be determined by analyzing the optical properties of plane-polarized light reflected from the surface of the films at a slightly oblique angle.34 The technique gains additional power when electrodes are added to the setup, allowing observation of the behavior of the films in the presence of an electric field parallel to the plane of the film.35... 

Most (but not all) LCDs require that the liquid crystal be uniformly oriented i.e., that the LC exist in the form of a single domain in either the OFF or ON condition. The required alignment can be brought about by imparting to the confining surfaces a unidirectional sense, either by rubbing or by the oblique evaporation of SiO or other compounds (Kahn, 1977). A variety of boundary conditions can therefore be set up, including some that result in a metastable behavior of the enclosed liquid crystal phase. 

One of the common surface structures of archea and bacteria are monomolecular crystalline arrays of protein subunits, called S-layers [106-109]. They constitute the outermost component of tlie cell envelope of these procaryotic organisms. S-layer subunits can be aligned in lattices with oblique, square, or hexagonal symmetry. Since S-layers are monomolecular assemblies of identical protein subunits, they exhibit pores of identical size and morphology. A group of nonclassical cell wall polymers, called secondary cell wall polymers (SCWPs), are attached noncova-lently, presumably by a lectin-type interaction, to the S-layer proteins. 

Figure 2. OCD of alamethicin in aligned multilayers of DPhPC (L P = 50 1) when the sample is in equilibrium with 100% relative humidity (RH) (spectra i) and with 50% RH (spectra S). CD was measured with light incident at an angle a relative to the normal to the planes of bilayers. The a dependence of spectra I indicates that the helical parts of alamethicin molecules are perpendicular to the plane of the bilayer, whereas the a dependence of spectra S indicates that the helices are parallel to the plane of the bilayer. The solid lines for the a — 0° spectra are the least-squares jits the solid lines for the spectra of oblique angles are theoretical constructions from the a = 0° spectra. (Reproduced with permission from reference 1. Copyright 1990.)...

The critical wavevector is perpendicular to, or subtends a large angle with the initial director alignment (contrary to normal rolls) thus, the rolls are parallel (longitudinal) or strongly oblique (see Fig. 13). 

Fig. 4.8. Oblique view of the right and left breast. There is a white area at the pectoral side of the right breast a small pectoral part of the right breast (black arrows) is missing and a gray vertical line is present (white arrows) due to alignment problems of the CR reader due to bad positioning of the IP in the CR reader (Fuji Protect CR)...

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