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High birefringence liquid crystal mixtures for electro-optical devices

Nowinowski-Kruszelnicki E., Kędzierski J., Raszewski Z., Jaroszewicz L., Kojdecki M., Piecek W., Perkowski P., Garbat K., Olifierczuk M., Sutkowski M., Ogrodnik K., Morowiak P., Miszczyk E.

Optica Applicata

2012

Vol. 42, nr 1

167--180

High-birefringence nematic liquid crystals recently developed in the Military University of Technology (Poland) are examined for selected physical properties. In particular, for six liquid crystal mixtures there were determined: two components of dielectric permittivity for voltage frequencies in the range from 10 Hz to 10 MHz; rotational viscosity; splay, twist and bend elastic constants; ordinary and extraordinary refractive indices for light wavelengths in the range from 0.3 ?m to 1.6 ?m. The properties are discussed in terms of applicability of the new liquid crystals to electro-optical devices.

Optical method for determining anisotropy of diamagnetic susceptibility of nematic and polar anchoring energy coefficient of nematic-substrate systems by using a cell of varying thickness

Kędzierski J., Raszewski Z., Kojdecki M., Zieliński J., Miszczyk E., Lipińska L.

Opto-Electronics Review

2004

Vol. 12, No. 3

299-303

A wedge cell of the wedge angle of the order of few milliradians was used to measure threshold magnetic fields for the magnetic Freedericksz transition [1-3]. A nematic liquid crystal filling the cell was of planar orientation enforced by the treatment of the flat boundary plates. A system of interference fringes appeared in the cell placed in normally incident light between analyser and polariser crossed. In the vicinity of each fringe, the cell could be considered as a flat-parallel one and hence it was equivalent to a system of flat cells of different precisely determined thickness, the same relates to any cell of slowly-varying thickness and flat cover plates. The threshold magnetic field magnitudes were interpreted as eigenvalues of the boundary eigenvalue problem for the operator of the second derivative; the interaction between the nematics and the substrate was described by the Rapini-Papoular formula [3] (i.e., weak coupling was considered). The resulting formulae were used to determine the polar anchoring energy coefficient and the anisotropy of diamagnetic susceptibility after the threshold fields measured. The method was applied to characterise the nematic liquid crystal 5CB and the coupling between it and the substrates made of poly(amic acid) MP2 [4, 5]. The estimates of material parameters agreed pretty well with those determined by the composite method [6].