Mauguin nematics

Figure 8.11 Illustration of Mauguin twisted nematic cell, reported in 1911. Substrates are thin mica plates, which are uniaxial with their optic axis parallel to plane of plates. Apparently, uniaxial crystal stmcture of mica produces strong azimuthal anchoring of nematic LCs of Lehmann, such that director is parallel (or perpendicular) to optic axis of mica sheets at both surfaces. Mauguin showed that method of Poincard could be used to explain optics of system if it was assumed that LC sample created layer of material with uniformly rotating optic axis in twisted cells.

Equation (4.1.15) implies that at any point in the medium there are two linear vibrations polarized along the local principal axes. The polarization directions of these two vibrations rotate with the principal axes as they travel along the axis of twist and the phase difference between them is the same as that in the untwisted medium. This result was first derived by Mauguin and is sometimes referred to as the adiabatic approximation. It is this property that is made use of in the twisted nematic device discussed in 3.4.2. 

Let the structure of the nematic liquid crystal be called uniform if the director distribution in this structure, and, accordingly, its optical and electrooptical properties are uniform, i.e., do not depend on the coordinates in the plane parallel to the substrates. The first observations of the optical and electrooptical properties of uniform nematic structures were carried out by Mauguin, Tsvetkov, and Prederiks over 50 years ago [1-4]. Since the beginning of the 1970s these structures have attracted growing interest, as they are the most promising ones for practical applications in Liquid Crystal Displays (LCDs). 

As was established a long time ago by Mauguin [11], pure twist deformations can be produced by placing a nonchiral nematic liquid crystal between two parallel rubbed solid surfaces and then rotating one plate in its own plane relative to the other. Such a structure is optically active despite the fact that the nematic molecules are not chiral. The twist is maintained by the surface azimuthal anchoring. 

Dorn [2] performed the first precise measurements of the principal refractive indices rif. and for the N and SmA phases of ethyl-4- [4-ethoxybenzylideneamino]-a-methylcinnamate using Abbe s total reflection method. Also later measurements on nematic liquid crystals by Gaubert [3] and Mauguin [4] were based on the determination of the boundary angle of total reflection. In 1950, Pellet and Chatelain [5] intro-... 

These optical properties of chiral nematic materials have all been observed experimentally. There have been quite extensive theoretical studies carried out by Mauguin [60], Oseen [61], and de Vries [26] to explain how these properties arise from the he-licoidal structure. Kats [62] and Nityanan-da [63] have derived exact wave equations to explain the propagation of light along the optic axis and Friedel [32] has reviewed the main textures observed with chiral nematics. We will outline the important elements of these studies in the next sections (Secs. 2.2.1.1 -2.2.1.3). In Sec. 2.2.1.4 we will consider how the helicoidal pitch, and... 

In these terms C. Mauguin reported in 1913 the first observation of the orienting action of freshly cleaved surfaces of the muscovite mica on a nematic liquid crystal p-azoxyanisole ... 

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