Kazuyuki Hiraoka

Stability of Antiferroelectricity and Causes for its Appearance in SmCα* and SmCA* Phases of a Chiral Smectic Liquid Crystal, MHPOBC

The smectic layer thickness and the switching behavior in MHPOBC have been studied as a function of temperature; SmCα* is a tilted phase and is antiferroelectric at least in the higher-temperature region but becomes ferrielectric with decreasing temperature. The gradual appearance of ferrielectric characteristics in SmCα* suggests the emergence of the Devils staircase. To explain the antiferroelectricity in SmCα* and SmCA*, two types of molecular interactions are proposed: one is the interaction between the spontaneous polarizations in the neighboring layers which is effective in SmCα*, and the other is the pairing of transverse dipole moments responsible for the antiferroelectricity in SmCA*.

Observation of three subphases in smectic C* of MHPOBC by dielectric measurements

In the phase transition from the paraelectric smectic A to the antiferroelectric SmCA* phase via the ferroelectric SmC* phase in MHPOBC, the existence of a subphase, SmCα*, between SmA and the normal SmC* (SmCβ*) was confirmed in addition to that of another subphase, SmCγ*, between SmC* and SmCA* by means of dielectric measurements. It was also confirmed that these subphases, SmCα* and SmCγ*, disappear in the same compound of lower optical purity as observed by DSC. The model structure of the SmCα* phase is speculated on the basis of the dielectric measurements.

Electric-Field-Induced Apparent Tilt Angle and Devil's Staircase in SmCα* of an Antiferroelectric Chiral Smectic Liquid Crystal

The SmCα* phase which was discovered between SmA and SmC* in 4-(1-metylheptyloxycarbonyl) phenyl 4-octyloxybiphenyl-4-carboxylate (MHPOBC) has been studied by means of electric-field-induced tilt angle measurements and conoscopic observation. The induced tilt angle increases not smoothly but stepwise in SmCα* and its neighboring SmA temperature ranges, suggesting successive structural changes, namely, Devils staircase. According to the conoscopic figures, the existence of the ferrielectric orientation was confirmed. Devils staircase observed as a result of changing field strength was discussed in comparison with that induced by changing temperature.

Electric-Field-Induced Transitions among Antiferroelectric, Ferrielectric and Ferroelectric Phases in a Chiral Smectic MHPOBC

A T-E phase diagram of MHPOBC (C8H17O–--COO–-COO*CH(CH3)C6H13) has been obtained by means of the temperature (T) dependence of the dielectric constant under a dc biased electric (E) field. It is presumed from the T-E phase diagram that there is a temperature range where the field-induced antiferroelectric-ferrielectric-ferroelectric phase transitions take place. These transitions have been confirmed as five transmittance states between crossed Nicols under a triangular wave, i.e., ferro-ferri-antiferro-ferri-ferro. The field-induced antiferroelectric-ferrielectric phase transition has also been identified through conoscopic observation.

Construction of Dynamic Conoscope Observation System Using CCD Camera and Image Processor

In order to study the dynamic behavior of conoscopic images with high precision and high efficiency, we constructed a conoscope observation system using a CCD (charge coupled device) camera and an image processor. We can analyze biaxiality and apparent tilt angle by means of a homeotropic cell operated at 0.1 Hz. We discuss the result obtained in an antiferroelectric liquid crystal, 4-1-(methylheptyloxycarbonyl) phenyl 4-octyloxy-biphenyl-4-carboxylate (MHPOBC).

Dielectric Behavior and the Devil's Staircase in the SmCα* Phase of an Antiferroelectric Liquid Crystal, 4-(1-methylheptyloxycarbonyl)phenyl 4′-octylcarbonyloxybiphenyl-4-carboxylate

We have observed an increase of the dielectric constant under a bias electric field in the SmCA* and SmCα* phases in 4-(1-methylheptyloxycarbonyl) phenyl 4-octylcarbonyloxybiphenyl-4-carboxylate. This implies a field-induced phase transition to the ferrielectric and/or to the ferroelectric phases. The transitions were also clearly observed in the field-induced apparent tilt angles in these phases. The electric-field-induced Devils staircase was confirmed in the SmCα* phase. Using these observations, a T(temperature)-E(electric field) phase diagram was drawn.

Spontaneous deformation of main-chain liquid-crystalline elastomers composed of smectic polyesters

We observe the spontaneous shape change of a uniaxially deformed liquid-crystalline elastomer composed of smectic main-chain liquid-crystalline polyesters in a cyclic heating–cooling process. Although the elastomer contracts by about 115% on heating up to the isotropic phase, the sample length recovers by 55% on cooling to room temperature in the first heating–cooling process, and the elastomer exhibits an almost complete reversible deformation in the second heating–cooling process. By a comparison of the results of sample observation with those of X-ray analysis, we recognise that the strain λ was linearly coupled with the orientational order parameter S. In addition, the results of the X-ray analysis imply that a cybotactic nematic state, in which smectic clusters lie scattered in a nematic-like matrix, emerges after exposure to the isotropic phase.

X‐Ray Diffraction Studies on the Phase‐Transformational Behavior of a Smectic Liquid‐Crystalline Elastomer Composed of Chiral Mesogens

Structural changes through successive phase transformations of a chiral smectic liquid-crystalline elastomer are investigated by X-ray scattering technique. In uniaxially deformed elastomers, the smectic layer seemingly tilts even in the SmA phase, in which an in-plane chevron structure formed in the tilted smectic phase. On the basis of an analysis of the layer reflection peaks, the layer correlation length in the tilted smectic phases is shorter than that in the non-tilted SmA phase, though smectic layers in the tilted smectic phases are better ordered than those in SmA.

Electroclinic and electromechanical effects of a side-chain chiral smectic A elastomer

Optical and mechanical responses to electric stimulation in a side-chain smectic A elastomer composed of a chiral mesogen have been investigated. The molecular tilt caused by the electroclinic effect in an electric field was measured optically in the chiral smectic A phase. In addition, the electric field also induced shear deformation in the elastomer, and the tilt angle of the sheared elastomer, defined as the angle made by the edge of the elastomer film and the direction of the layer normal, was smaller than the molecular tilt angle estimated by optical measurement.

13C-NMR Spin Lattice Relaxation Time Observation on the Smectic A and Smectic C* Phases of a Chiral Smectic Liquid Crystal, (S)-4-(1-methylhexyloxycarbonyl)phenyl 4'-octyloxybiphenyl-4-carboxylate

In order to study molecular rotation around the long axis in chiral smectic phases, the temperature dependence of the spin-lattice relaxation time T1 is investigated in a ferroelectric liquid crystal, (S)-4-(1-methylhexyloxycarbonyl)phenyl 4-octyloxybiphenyl-4-carboxylate (S-MH(6)POBC) by means of solid-state 13C-NMR spectroscopy. The spin-lattice relaxation time T1 of the aromatic core increases with increasing temperature in the smectic A (SmA) and chiral smectic C (SmC*) phases, because the frequency of the molecular rotation dominating the spin-lattice relaxation process is higher than the Larmor frequency ω0 of 100 MHz in the present measurement. In addition, the temperature dependence of T1 reveals that the activation energy of the molecular rotation in the SmC* phase is lower than that in the SmA phase.