Herein, we report that liquid crystal displays (LCDs) such as TN (twisted nematic)-mode, TB (tunable birefringence)-mode, VAN (vertically aligned nematic)-mode, BN (bent nematic)-mode,
and so forth, exhibit the reduction in the operating voltage and response times by doping the nanoparticles of inorganic substances such as MgO. These effects may be attributed to the modification of the physical properties of the liquid crystal host media in these LCD cells.
TN-LCDs fabricated by doping metal nanoparticles of such as Pd, Ag, Au, or Ag-Pd composite are shown to exhibit a frequency modulation electro-optic response with short response time of ms or sub-ms order. These devices are called FM-LCDs. The frequency range spreads from 40 Hz to 2 KHz around a dielectric relaxation frequency that increases with increasing the concentration of metal nanoparticles. This behavior is explained by the equivalent circuit model of heterogeneous dielectrics, for the first time, formulated by the present authors. Further, we discuss the origin of the fast response and the value of electrical conductivity of metal nanoparticles.
Electro-optic characteristics of a twisted nematic (TN) liquid crystal display (LCD) fabricated by doping Ag nanoparticles protected with NLC, 5CB (K-15, Merck) molecules has been investigated and it is shown that the device exhibits a unique electrooptic response characteristics that is sensitive to the high frequency component of the operating voltage together with the conventional root-mean-square response to the operating voltage. We call this device frequency modulation (FM) TN-LCD. The FM TN-LCD is switched by switching the frequency of the operating voltage while its amplitude is kept unchanged. As an example, by switching the frequency from 20Hz to 500Hz or 50Hz to 2kHz, and the switching is done with the time constant of several ms. This device shows a peculiar response to a burst AC square voltage waveforms, where the device exhibits bipolar response with the time constant of 500 ms and the envelope with the time constants shorter than those of an undoped TN-LCD by from 30% to 80%. The mechanism of the FM-TN-LCD is investigated through the study of its dielectric properties.
The effect of the photoalignment on the electrooptic characteristics of polymer stabilized ferroelectric liquid crystal displays (FLCDs) exhibiting V-shaped switching and those of FLCDs exhibiting half-V switching are reported and discussed. Photoalignment technique and hybrid alignment, which is done by combining photoalignment and rubbing, are shown to be useful for fabricating zig-zag defect-free FLCDs and improving the electrooptic characteristics of FLCDs-SSFLCDs, V-F-LCDs, and H-V-FLCDs- especially in the reduction of operation voltage.
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