Information Recording in Photosensitive Photonic Cholesteric Liquid Crystal

According to the modern conceptions the cholesteric liquid crystals (CLCs) can be considered as one dimensional 1D) photonic crystals. The existence of the selective reflection band and the ability to change the selective reflection avelength over a wide range under the action of applied external forces make it possible to use the CLCs in the data ecording, processing and storage systems. Presently, the interest is focused on materials with photo controlled optical roperties. We propose the use of the photo controllable selective reflection as the modulated parameter. We used a cholesteric mixture with photoisomerizable molecules and CLC layer with planar orientation sandwiched etween two glass plates. Under UV irradiation the CLC layer changes the selective reflection wavelength [1–4]. hrough a mask covering the pattern, gratings in this structure were recorded. A polymer stabilizer was doped to the ixture to avoid fluidity of the CLC after preparation of the pattern. In our experiments we used a cholesteric mixture of the nematic Zhk-440 (from NIOPIK, Moscow) and optically ctive dopant MLC-6248 (from Merck, Germany). ZhK-440 is an azoxy-component mixture of 2/3 p-n-butyl-pethoxyazoxybenzene and of 1/3 p-nbutyl-p-heptonoiloxyazoxybenzene. It is enough transparent in the visible range f spectrum and absorbs in the UV part (Fig. 1). The used chiral dopant MLC-6248 is a transparent and non photo sensitive compound whose concentration in he CLC mixture is responsible for the selective reflection wavelength of the CLC layer. The mixture 74.4%Zhk40 + 25.6%MLC-6248 was selected due to its most suitable photoand thermo-optic parameters. The temperature ependence of selective reflection wavelength of this mixture near room temperature is quite weak (Fig. 2,a). Exposure to UV shifts the selective reflection band (color) from red to green (Fig. 2,b). The shift of reflection band epends on exposure time and thickness of the cell. A 100W Mercury lamp was used as a light source. By means of a mask covering the pattern, gratings in these structures were recorded (Fig. 3). The gratings represent nterchanging color stripes. The difference between colors depends on the exposure time. In Fig. 3,b besides gratings he exposed and initial areas of the sample are also shown.