A new method of generating color in liquid crystal displays using birefringent filters is shown. This method has the benefit of high light transmission and color saturation compared to traditional spatial or temporal multiplexing methods, which include highly absorptive color filters. We discuss the design and optimization of a double-layer supertwisted nematic color display based on polarization interference filters. The viewing angle of such a device is also modeled and improvements are shown. The device is capable of high light transmission (90% that of parallel polarizers) while retaining color saturation.
Method for Fabrication of Liquid-Crystal Cells with Narrow Gap, Fast Switching, and Flexible Plastic Substrates06/01/2006
A phase-separation method for the construction of devices with specific internal architecture of LC/polymer composite system is presented. The method results in adjacent uniform polymer and LC films parallel to the substrates. Scanning electron microscopy was employed to investigate the internal structures. The results show that the thicknesses of the LC and the polymer films in cells constructed with fixed-size spacers directly depends on the LC/polymer in the initial mixture. This can be effectively used for precision cell-gap control and to fine-tune the LC optical path length. Cells with a submicrometer gap, prepared with this method and with 35 wt.% of LC in the mixture, exhibited a total response time approaching 1 msec. This method has also been used to fabricate devices with plastic substrates.
The formation of different structures in phase-separated composite films (PSCOFs) from formulations of liquid crystals and photocurable monomers has been investigated using polarizing optical and scanning electron microscopies. Two processes, spatially nonuniform polymerization and diffusion of small molecules, play important roles in determining a specific PSCOF polymer structure. The variations in UV irradiation intensity and temperature, at which phase separation is carried out, strongly influence these two processes and can change the resultant structure from a homogeneous PSCOF bilayer structure to a heterogeneous polymer dispersed liquid crystal (PDLC) structure. A variation in cell thickness changes the distance through which small molecules have to diffuse during phase separation and, thus, affects the structure obtained in thick and thin cells.
Control of Nematic Director Orientation By Exposing Rubbed Polyimide Films To Linearly Polarized Ultraviolet Light11/24/1997
The delicate interplay between the effects of mechanical rubbing and subsequent photo-induced chemical reactions on polyimide films has been studied for aligning liquid crystals. Exposure to linearly polarized ultraviolet (LPUV) light was found to profoundly alter the direction and the degree of molecular orientations obtained by rubbing. A simple model is presented to describe the observed changes in the director orientation. The results show that LPUV exposure can be very effectively used to control and fine-tune liquid crystal alignment.
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The results of a recent investigation of the nematic biaxiality in a bent-core mesogen (A131) are in apparent disagreement with earlier claims. Samples of mesogen A131 used in the two studies were investigated with polarized optical microscopy, conoscopy, carbon-13 NMR, and crossover frequency measurements. The results demonstrate that textural changes associated with the growth of biaxial nematic order appear at similar to 149 degrees C. The Maltese cross observed in the conoscopic figure gradually splits into two isogyres at lower temperatures indicating phase biaxiality. Presence of the uniaxial to biaxial nematic phase transition is further confirmed by temperature trends of local order parameters based on (13)C chemical shifts in NMR experiments. Frequency switching measurements also clearly reveal a transition at 149 degrees C. Differences between the two reports appear to be related to the presence of solvent, impurities, and/or adsorbed gases in samples of A131 used in the study of Van Le et al. [Phys. Rev. E 79, 030701 (2009)]