ИСТИНА

A nematic composition LC-1277 and a monomer bisphenyl-A-dimethacrylate were used in the process of investigation of electrooptics of nematic liquid crystals stabilized by a polymer net (PNLC). The sample polymerization was due to the action of UV radiation. The cell thickness dependences of the Frederiks threshold voltage and the electrooptical effect off time were measured for pure NLC-1277 and PNLC samples. As a result, first it was shown that the Frederiks threshold voltage for pure NLC was independent of the layer thickness, while it was growing linearly with the layer thickness for PNLC. Second, the optical response off time for pure NLC was growing proportionally to the square of the layer thickness, while it remained constant for PNLC. These experimental results could be explained by the domain structure of PNLC, when a liquid crystal inside an electrooptical cell consisted of the oriented areas divided by thin walls of polymer material. 5CB nematic and physical net created by 12-hydroxy octadecanoic acid were used, when the electrooptics of nematic liquid crystals stabilized by a physical net was explored. The following electrooptical properties of this material were studied: the dependences of the light transmission and of the on and off times upon the electric voltage. As a result, two on times were found. The first one was related to the nonthreshold reorientation of the director field. The second appeared when the applied voltage exceeded the Frederiks threshold. Two off times were discovered as well. They both were dependent on the applied voltage in the area of weak fields. As the electric field strength was growing, they both reached the saturation values. The value of these times was about one millisecond, i.e. three orders of magnitude lower than it was for analogous samples of pure liquid crystals. Such electrooptical behavior of the investigated material was related to the fact that a gelling agent created a strongly defected structure inside liquid crystal, which consisted of two systems of liquid crystalline areas – planar and tilted. The effective sizes of these areas were variable and considerably less than the cell thickness.