Atsuo Fukuda

Discovery of a novel ferrielectric phase of five-layer periodicity in binary mixtures of chiral smectic liquid crystals exhibiting unusual reversed phase sequence

In a binary mixture system of ferroelectric and antiferroelectric liquid crystals whose major component shows an unusual reversed phase sequence of , a new phase with ferrielectric order of five layers has been discovered by the electric field-induced birefringence (EFIB) measurements. The EFIB was measured using a photo-elastic modulator (PEM) set-up and by applying an in-plane electric field to a homeotropic aligned cell filled with the binary mixtures of compounds with ferroelectric and antiferroelectric compounds. The contours of constant birefringence in the electric field–temperature (E–T) phase diagrams clearly indicate a distinct region corresponding to a new phase bordering the four-layer on the low temperature side and on the high temperature side. This new phase is unambiguously assigned to whose structure has been calculated by Osipov and Gorkunov.

Degeneracy lifting near the frustration points due to long-range interlayer interaction forces and the resulting varieties of polar chiral tilted smectic phases

To gain a clear understanding of ferroelectricity and antiferroelectricity together with their frustration in chiral tilted smectic liquid crystals, we have constructed E–T phase diagrams by drawing field-induced birefringence contours in the prototype binary mixture system of MHPOCBC and MHPOOCBC. The results obtained are discussed in terms of the theoretical model proposed by Emelyanenko and Osipov; we have insisted on the appropriateness of specifying the biaxial subphases, which emerge sequentially in the temperature-induced transition, by the relative ratio of ferroelectric and antiferroelectric orderings in the superstructure unit cell, such as , where qT  = [F]/([A] + [F]). Additional subphases other than the ordinary subphases with three- and four-layer superstructures, and , have been established to exist, firmly for and less adequately for and . Likewise, we have observed several stable superstructures during the field-induced transition from the biaxial subphases to unwound SmC*, and have tried to specify them using qE  = |[R] − [L]|/([R] + [L]), where [R] and [L] refer to the numbers of smectic layers with directors tilted to the right and to the left, respectively, in a unit cell of the superstructure. We have also found the characteristic field-induced deformation of the uniaxial subphase and attempted to understand it in terms of the devils staircase due to soliton condensation reported recently by Torikai and Yamashita ( 41 ).

V-shaped switching due to frustoelectricity in antiferroelectric liquid crystals

Abstract We have reinforced the assertion that the devils staircase and the thresholdless, hysteresis free, V-shaped switching are two manifestations of the frustration between ferro-and antif-erro-electricity, emphasizing that the third nearest neighbor interaction parameter may become negative, i.e. J 3 < 0. Three important consequences are: (1) The subphase with q=1/6 becomes to exist stably even in the ground state. (2) A number of subphases emerge and may apparently look like a single subphase. (3) It is not easy to distinguish SC* from frustrated subphases with small q numbers. We have summarized compounds and mixtures for the Y-shaped switching that are described in Japanese Patent Gazettes open to public recently. The materials show an antiferroelectric, probably q=1/6, subphase or an apparently single subphase in a wide temperature range; some of them are characterized with novel chiral parts.

TARGET RESPONSE TIMES OF LIQUID CRYSTAL DISPLAYS ESTIMATED BY ANALYZING THE FRONT AND REAR PART GRAY LEVELS OF MOVING SQUARE PATTERNS

The slow response of nematic materials causes the blurring of moving pictures on commercial liquid crystal displays (LCDs). We have estimated the critical response time τ90 necessary for apparently eliminating the blurring as a function of the gray level difference ΔG. The estimation is based on the observation that a running square pattern is hardly perceived when it differs from the background only by one in the 256 gray scale. For example, τ90 is 300 µs for ΔG=255 and 10 ms for ΔG=3, which can be attained by using advanced smectic materials with ferro- and/or antiferroelectricity. Comments are given on another cause of blurring due to the characteristic feature of hold-type displaying in LCDs.

Antiferroelectric and ferroelectric orderings in frustrated chiral tilted smectics and a continuous change from anticlinic SmCA* to synclinic SmC*

In a frustrated binary-mixture system of ferroelectric and antiferroelectric liquid crystals, where the border line between SmCA* and SmC* in the temperature-concentration phase diagram runs almost parallel to the ordinate temperature axis, we have found a continuous change between them close to the critical concentration. The continuity has been confirmed as an intrinsic property in the bulk by observing almost perfect bell-shaped Bragg reflection bands due to the helicoidal director structure. The temperature variation of peak wavelength of the half-pitch band and, in particular, the characteristic disappearance of the full-pitch band apparently within the SmC* temperature region have been simulated with a change in the ratio of ferroelectric and antiferroelectric orderings. The observed continuous change has been described by the entropy effect in the 1D Ising model with the synclinic and anticlinic orderings as spins.

Antiferroelectric dielectric relaxation processes and the interlayer interaction in antiferroelectric liquid crystals

Antiphase relaxation process of antiferroelectric phase is investigated in binary mixtures of antiferroelectric and ferroelectric liquid crystalline compounds. It is found that the frequency of the antiphase mode ranges from 2to4MHz, being one of the fastest collective processes reported so far. This can be exploited in a photonic switch with a submicrosecond response time. However, the frequency of the antiphase mode decreases by the mixing ratio of the ferroelectric compound. The decrease in the frequency is shown to be due to a reduction in the elastic constant in between the adjacent layers.

Synclinic and anticlinic ordering in frustrated smectics

Molecular origin of synclinic and anticlinic ordering in the smectic-C and smectic-CA phases is considered in detail. The model potential for the anticlinic phase is proposed and possible contributions between various intermolecular interactions are discussed. It is concluded that conventional dispersion and steric interactions between mesogenic molecules generally do not promote the Sm-CA phase. A particular model of the anticlinic phase is proposed which is based on interlayer orientational correlations between transverse molecular dipoles located in the flexible chains. Such correlations are not sensitive to molecular chirality and thus the theory accounts for the formation of the anticlinic phase in racemic mixtures. Finally the microscopic origin of ferrielectric and antiferroelectric subphases is discussed and the concept of the ‘discrete’ flexoelectric effect is introduced which can in principle be used to explain the particular structure of subphases.

Devil' Staircase and Frustoelectricity in Chiral Smectic-C like Liquid Crystals

Abstract In 1989, Chandani et al. showed that the tristable switching, already observed by themselves and by others in 4-(1-methylheptyloxycarbonyl) phenyl 4′-octyloxybiphenyl-4-carboxylate (MHPOBC).

Renewed focus on the small temperature change of smectic layer spacing in ferroelectric and antiferroelectric LCs

We aim at becoming released from the invisible hand of de Vries scenario that a small temperature change in the smectic layer spacing must be caused by ‘the far-fetched orientational distribution called the de Vries diffused cone’ or ‘the in-layer directors statically tilted and randomly distributed around the smectic layer normal’. First, we show in a prototypal compound MC513 that all the unusual properties suggesting the revival of a de Vries-type SmA-Sm transition can be explained by ordinary SmA emergence just below the isotropic phase only in a narrow temperature range. Second, we take up the unconventional molecular structure of TSiKN65, thus far regarded as a typical de Vries material; the core part makes a large angle of with respect to the average molecular long axis. We insist that a slight change in can explain almost all the unusual properties without taking account of the de Vries scenario. Last but not least is a practical point of view. During a thermal shock cyclic reliability test between −20°C and 60°C in prototyping antiferroelectric liquid crystal displays (AFLCDs), DENSO noticed the importance of the transition from Sm to the hexatic or crystalline phase; the cell quality critically depends on the layer spacing change in the lower-temperature part of Sm. We point out that the relative displacements of molecules along their long axes and hence the layer undulational fluctuations play an important role in addition to the director tilting ones.

Structure of Needlelike Defect in Homogeneously Aligned Cells of a Ferroelectric Liquid Crystal Mixture Studied Using X-Ray Microbeam

Using a synchrotron X-ray microbeam, we analyzed the structure of needlelike defects running parallel to the rubbing direction in virgin homogeneously aligned cells of ferroelectric liquid crystals. It was found that the local layer of the defect is perpendicular to the substrate plane and the layer normal is tilted from the rubbing direction, which is similar to the model proposed by Shao et al.. [Ferroelectrics 121 (1991) 127]. It was also found that the detailed structure depends on the cell thickness.