Takanari Yamaguchi

Cubic phases of 4′-n-alkoxy-3′-nitrobiphenyl-4-carboxylic acids (ANBC-n)

The structure of the thermotropic cubic phases of 4′- n -alkoxy-3′-nitrobiphenyl-4-carboxylic acids (ANBC- n , where n indicates the number of carbon atoms in the alkoxy group) was studied by X-ray diffraction. For the homologues with n = 15, 16, 17, and 18, the cubic phase was of an Ia 3 d type, whereas the homologues with n = 19, 20, and 21 exhibited an Im 3 m cubic structure; for these seven homologues the same type of cubic structure was observed both on heating and cooling. Further lengthening of the alkoxy chain to n = 22 and 26, however, gave two types of cubic structure in the cubic phase region on heating, one with Im 3 m symmetry in the low temperature region and the other with Ia 3 d symmetry in the high temperature region. On cooling, the two homologues exhibited the Ia 3 d cubic structure only. This is the first example in the cubic phase region of a series of homologues containing two types of structure, dependent on temperature and n . Such a complicated phase diagram in the cubic region is clearly understood qualitatively in terms of Gibbs free energy-temperature diagrams. The dependence of structural parameters such as the cubic lattice constant on the alkoxy chain length n are also presented and discussed.

Dynamic viscoelastic properties of D-phase compounds

Abstract Dynamic viscoelastic properties were studied for two D-phase compounds, 4′- n -hexadecyloxy- and 4′- n -docosyloxy-3′ carboxylic. acids. The storage modulus ( G ′) in the D phase showed an extraordinary high value of 10 7 dyne/cm 2 , compared with that in smectic A and C phases. These viscoelastic results suggest the existence of a three-dimensional network structure constructed by rod-like micelles, as proposed by Tardieu and Billard.

Syntheses and physical properties of ferrocene derivatives (XIV) dynamic viscoelastic property of liquid crystalline ferrocene derivatives containing cholesteryl group as a mesogenic one

Abstract The dynamic viscoelastic properties for [4-[ω-(cholesteryloxy carbonyl)alkoxycarbonyl]phenyl]ferrocenes with hexyloxy and octyloxy groups as an alkoxyl group were measured as functions of temperature and frequency. These samples showed liquid crystallinity. The results obtained here suggest that a kind of molecular order exists in the temperature range from the clearing point to about 20 degrees above it, in the liquid phase. Furthermore, the values of apparent activation energy in the liquid crystalline phase are as large as those of a primary dispersion of polymers, and its activation energy is not affected by the structural change at the clearing point.

Cubic Phases of 4'-n-docosyloxy-3'-nitrobiphenyl-4-carboxylic Acid (ANBC-22)

Dilatometric experiments have been performed on 4′-n-docosyloxy-3′-nitrobiphenyl-4-carboxylic acid (ANBC-22) which exhibits two types of thermotropic cubic phases (Cub I and II) on heating. Although the unit lattices of both Cub I and II, determined by X-ray diffraction measurements, slightly but certainly shrink with increasing temperature, the thermal expansion coefficients in both temperature regions were found to be positive. Thus, this study provided an experimental evidence that the number of molecules constructing the unit lattice of the two Cub phases decreases with temperature. Some aspects of the structural features of the Cub phases are discussed.

Dynamic mechanical properties of strontium stearate

Abstract The dynamic modulus (G′) and the loss (G″) were measured as a function of temperature for strontium stearate which undergoes successive phase transitions from crystal (Cr)–unknown liquid crystalline (lc) (X), rhombohedral lc (R), body-centered cubic (Q) and hexagonal lc (H) phases. This Letter shows that in the Q phase only, G′ and G″ undergo a thermal hysteresis and in the Q phase, the G′ and G″ values were smaller during cooling from the H phase than during heating from the R phase and G′ was smaller than G″ in the cooling process. From these results, the formation and structure of the Q phase are discussed.

Cubic D Phase of 4′-n-Pentadecyloxy-3′-Nitrobiphenyl-4-Carboxylic Acid

Abstract The phase behavior of 4′-n-pentadecyloxy-3′-nitrobiphenyl-4-carboxylic acid (ANBC-15, where “15” corresponds the number of carbons in the alkoxy groups) was investigated by differential scanning calorimetric, polarizing optical microscopic, infrared spectroscopic and dynamic viscoelastic (DVE) measurements. ANBC-15 has a critical alkoxy chain length for exhibiting the cubic D (CubD) phase in ANBC series, and the virgin sample of ANBC-15 shows the CubD phase on heating, but the appearance of the CubD phase in the second heating depends on the turnover temperature of the preceding heating. Such instability of the CubD phase was also observed by isothermal frequency scans of DVE, which reveals the existence of a crossover of the storage and loss modulus curves, reflecting a structural fluctuation of the CubD phase in ANBC-15. The instability of the CubD phase of ANBC-15 is suppressed by mixing 25 mol % of ANBC-16, resulting in an enantiotropic CubD phase.