The orientation dynamics of a ferroelectric liquid crystal with a naphthalene ring (FLC-3) during the electric-field-induced switching between two surface-stabilized states was investigated by means of time-resolved Fourier-transform infrared spectroscopy. Time-resolved infrared spectra of the planar-aligned cell of FLC-3 were measured as a function of the polarization angle ranging from 0 degree to 180 degrees under a rectangular electric field +/-40 V with a 5-kHz repetition rate in the smectic-C* (Sm-C*) phase at 137 degrees C. From these spectra details about the mutual arrangement of different molecular segments at all the delay times in the Sm-C* phase were derived. It was found that the C=O group in the core moiety exhibits a dynamical behavior different from that in the chiral moiety during the electric-field-induced switching between the two surface-stabilized states. The most important finding in the present study is that during the electric-field-induced switching the FLC molecule not only rotates around the layer normal, but also revolves around its own long axis. Furthermore, time-resolved infrared spectroscopy revealed that each group in the core moiety passes almost simultaneously through the projection of the layer normal in the cell window during the dynamic switching.
Abstract We have newly developed flexible electronic paper using an easily‐controlled adhesive column spacer that forms cell gaps and improves the aperture ratio without using bead spacers. The reflectance of this new, flexible, full‐color prototype with low‐ power driving is 33%, its contrast is over 6, and it can display 262,144 colors.
A theory to explain the polarization-angle dependence of polarized infrared spectra of a ferroelectric liquid crystal in the surface-stabilized ferroelectric liquid crystal state is proposed. It describes the relationship between the intensity of the absorption bands and the polarization angle of the infrared radiation. Using this theory the polarization-angle dependence of the infrared band intensities was analyzed for a ferroelectric liquid crystal with a naphthalene ring and two phenyl rings with a stacked layer structure in the smectic-C* phase. The polarization-angle-dependent spectra were measured at 137 degrees C under external dc electric fields of +40 and -40 V to investigate the orientation of the molecules. Plots of the infrared absorbance versus polarization angle for representative bands were subjected to a curve fitting procedure by a least squares method. From the curves obtained the orientation of the transition dipole moments with respect to the molecular long axis and the orientation of the molecular long axis with respect to the rubbing direction of the cell were estimated based upon the suggested theory. The polarization-angle-dependent infrared spectra obtained were also analyzed by two-dimensional (2D) correlation spectroscopy. The 2D correlation analysis clearly detects a slight phase difference in the polarization-angle dependence which is hardly recognized in ordinary plots of the intensity changes in the infrared bands. The 2D correlation analysis allows us to separate asymmetric and symmetric stretching bands due to the chiral methyl group from those arising from other methyl groups in the alkyl chains.
The transient currents were observed in nematic liquid crystal (LC) cells when the polarity of the applied square wave voltage was reversed. The magnitude of these currents were shown to increase when the used LCs have a tendency to form dimers and the orientation films have a high electrical polarization. The origin of the transient currents is explained by assuming the switching of LC layers associated with the bilayers made of decomposed monomers adsorbed on the orientation films. The origin of the crosstalk appearing in the STN dot matrix LCDs is discussed in conjunction with the decomposition of dimers in the surface alignment region.
Abstract We confirmed that, for electronic paper that uses the cholesteric liquid crystal method, a high reflectance and contrast ratio were obtained by applying cross‐rubbing of appropriate rubbing strength to a high pretilt angle alignment layer.
Abstract Dynamic drive scheme (DDS) is known widely as passive matrix addressing that obtains both high‐speed re‐writing and a high contrast ratio in the field of cholesteric liquid crystal displays (LCDs). However, DDS has a serious problem in that the proper drive condition is very narrow and it is largely influenced by individual differences in LCDs that arise during their production. We have developed a new auto‐calibration system that adjusts both the contrast ratio and color balance automatically using capacitances of effective pixels and temperature compensation models that utilize the physical properties of cholesteric LCDs. We have managed to optimize the driving conditions between 5 and 35 °C with this method, and obtained both stable and high‐quality color images where the reflectance is 36%, contrast ratio is 8, and NTSC ratio is 20%. This auto‐calibration system has been able to greatly improve the production yield of cholesteric LCDs and made it possible to make practical use of cholesteric LCDs.
The orientation dynamics of a ferroelectric liquid crystal (FLC) with a naphthalene ring and without a carboxylate group near the stereocenter (FLC-2) during the electric-field-induced switching has been investigated by time-resolved infrared (IR) spectroscopy combined with normalized sample−sample two-dimensional (2D) correlation spectroscopy. To reveal the orientation dynamics, we have proposed a normalized sample−sample 2D correlation spectroscopy that is calculated by normalizing a sample−sample 2D correlation spectrum over every column or row. An important advantage of the normalized sample−sample 2D correlation spectroscopy over sample−sample 2D correlation spectroscopy is that the excessive information is deleted and more precise information therefore can be extracted even from spectra with a rather low signal-to-noise ratio. The normalized sample−sample 2D correlation spectroscopy allows us to explore the differences in the dynamics of each segment more clearly than the usual sample−sample 2D correlation spectroscopy. Time-resolved IR spectra of FLC-2 in a planar-aligned cell were measured over two delay time ranges from 0 to 150 μs and from 200 to 350 μs at an interval of 10 μs with the polarization angle of 45.0° under a rectangular electric field of ±3 V with a 2.5 kHz repetition rate in the smectic-C* (Sm-C*) phase at 115 °C. The normalized sample−sample correlation spectroscopy was applied to these time-resolved spectra. We explored the reorientation process of the alkyl chains, the core, and the carboxylate group of FLC-2 in the positive and negative half-periods of the electric-field-induced switching. It has been found from the present study that the reorientation track of the core in the positive half-period is different from that in the negative half-period, while the reorientation tracks of the CO dipole moment and alkyl chains are very similar between the positive and negative half-periods. The present study has also revealed that the orientation profile of the core moiety is different from those of the alkyl chains and the CO dipole moment, and the difference in the profile depends on the change of dc electric field from −3 to +3 V and from +3 to −3 V at an interval of 0.25V . It seems that the core moiety functions in the presence of memory properties. Furthermore, a tilt angle for FLC-2 with a naphthalene ring and without a carboxylate group near the stereocenter is smaller than other similar FLCs with a naphthalene ring and a carboxylate group near the stereocenter. It has been suggested from the analysis of the polarization-angle dependent spectra under the external dc electric field of two polarities that the carboxylate group near the stereocenter plays an important role in forming a large tilt angle and that the carboxylate group in the core moiety is responsible for the emergence of ferroelectricity.
A multicolour projection display with a bright screen and large information capacity has been developed using nematic-cholesteric (NC) liquid crystals (LCs). Through investigation of light scattering in the focal-conic state of the LC layer, the authors found that the transmittance depends on the light wavelength, because of diffraction scattering, and that the colour of light transmitted through the layer can be controlled by the birefringence and the thickness of the LC layer. A 640-*400-pixel multicolour projection display was fabricated using a two-layered LC panel, each layer passing green and red light under the focal-conic state. The Munsell chroma value was 6 for both of the projected colours. The projector also provides excellent white and black, because of the high transmittance of the nematic state and the subtractive mixture of complementary colours.< >
The dynamics of a ferroelectric liquid crystal with a naphthalene ring (FLC-3) during the electric-field-induced switching between two surface-stabilized ferroelectric liquid crystal states were investigated by time-resolved infrared (IR) spectroscopy combined with two-dimensional (2D) correlation spectroscopy. Time-resolved IR spectra of FLC-3 in a planar-aligned cell were measured as a function of the polarization angle range from 0° to 180° under a rectangular electric field of ±40 V with a 5 kHz frequency in the smectic- C* (Sm- C*) phase at 137 °C. From these spectra we explore details about the reorientation process of the alkyl chains, the core, and the large C=O dipole moments of FLC-3 at all the delay times. The 2D correlation spectroscopy was applied to the polarization-angle-dependent spectra for different delay times and to the time-resolved spectra at certain polarization angles to reveal the relative orientation of the C=O groups and the core moiety during the electric-field-induced switching. It was found from the present study that the relative orientation of the C=O groups and the core remains unchanged during the initial period of the reorientation, while it is reversed at a certain moment and then kept unchanged again. Moreover, the alkyl chains, C=O groups, and core moieties posses different dynamics during the fast course of electric-field-induced switching by analyzing time-resolved spectra.
