Kenji Nakao

Instability of conducting polymer, poly (3-alkylthiophene) gel with solvent, temperature and doping and effect of alkyl chain length

Abstract Volume, shape and color of poly(3-alkylthiophene)s change drastically with solvent composition and temperature, which is interpreted as characteristic behaviour of conducting polymer gels. Volume shrinkage ratio is larger in a chemically prepared sample than in an electrochemically prepared sample and also depends on alkyl chain length. Drastic shrinkage of poly(3-alkylthiophene)s in chloroform is also observed by adding iodine, which are explained by the formation of apparent cross-linking between polymer main chains by doping. These instabilities are reversible and also are considered to be candidates of molecular actuators.

Magnitude and direction of the spontaneous polarization of ferroelectric liquid crystals with several bond moments

Abstract The magnitude and direction of the spontaneous polarization in most ferroelectric liquid crystals have been confirmed to be determined by the location and magnitude of the bond moment around the chiral carbon and the core. In compounds with several bond moments their relative orientation is very important for obtaining a large spontaneous polarization. Compounds with benzene rings in the core substituted with OH also have a large spontaneous polarization, perhaps due to the formation of hydrogen bonds. Reversal of the direction of the spontaneous polarization with temperature has been found for EFPPOPB. This anomalous behaviour has been explained tentatively in terms of a conformation change due to the existence of a flexible -CH2- unit between the chiral carbon and the dipole moment.

Influence of hydrostatic pressure on electrical and optical properties of fusible conducting polymer at around melting point

Abstract Remarkable changes of electrical and optical properties have been observed in poly(3-alkylthiophene) with the hydrostatic pressure. The melting point increases by pressure with a rate of 20 °C/kbar. Electrical conductivity in the solid phase was enhanced by pressure but not in the liquid state. The blue shifted absorption peak at high temperature shifted again to lower energy and comes back to the original low temperature spectrum. These results are explained in terms of introduction of torsioning of some bonds between thiophene rings at high temperature and its suppression under hydrostatic pressure.

Photoluminescence of poly(3-alkylthiophene) under hydrostatic pressure

Photoluminescence of poly(3-alkylthiophene) in the liquid state is very noticeably enhanced under hydrostatic pressure. However, at high pressures above the liquid-solid transition, the luminescence intensity decreases and the emission peak shifts to a lower energy. These results are tentatively explained in terms of a change of the torsion angle at the bond between thiophene rings and the resulting change of effective conjugation length under pressure.

The characteristic dielectric behaviour in ferroelectric liquid crystals at a phase transition and the contribution of the soft mode

Abstract The characteristic dielectric behaviour of ferroelectric liquid crystals with a large spontaneous polarization has been studied as functions of the D.C. bias field, frequency, cell thickness and applied pressure. Under the condition in which the contribution of the Goldstone mode is suppressed, a sharp peak in the temperature dependence of the dielectric constant is clearly observed at the transition between SA and S*C phases T S C *s A. The relaxation of the soft mode is observed both in the SA and S*C phases by eliminating the contribution of the Goldstone mode under a D.C. bias field. Another relaxation is also observed in the S*C phase around several kHz in addition to that of the soft mode and the Goldstone mode. The pressure effect on the soft mode was also studied.

Anomalous temperature dependence of the dielectric and optical properties in ferroelectric liquid crystals

Abstract The anomalous temperature dependence of the sign of the spontaneous polarization in a biphenyl ester series of ferroelectric liquid crystals is reported. The reversal of the sign of the spontaneous polarization in the chiral smectic C phase of 2MBNCBC ((S)-2′-methylbutyl-4′-n- nonylcarbonyloxy-(l,l′-biphenyl)-l-carboxylate) is observed at T m. This anomaly is studied in detail as functions of the length of the terminal alkyl chain, the applied electric field, the frequency and the applied hydrostatic pressure. T m has been confirmed to depend on the length of the terminal chain and the applied pressure. However, it is independent of the applied field and the measuring frequency. In the mixture of these compounds, this anomaly is also observed.

Reversal of Spontaneous Polarization Direction in Ferroelectric Liquid Crystal with Temperature

Anomalous dielectric behavior in biphenyl ester series of ferroelectric liquid crystals are reported. Even in the chiral smectic-C phase, the spontaneous polarization becomes zero at a certain temperature-Tm and increases again below Tm with decreasing temperature. Moreover, At Tm the reversal of the sign of tilt angle is observed, indicating the reversal of the sign of the spontaneous polarization. However, this anomaly is not observed in the measurement of the helicoidal pitch and is not influenced by the application of pressure below several kbar. The origin of this anomaly is also discussed in terms of molecular interactions and conformation.

Effect of Molecular Structure of Core on Ferroelectricity in Ferroelectric Liquid Crystals

By using various couples of ferroelectric liquid crystals with molecular structures which were only different in the core center in each couple, the effect of the bond moment C=O at the center of core on ferroelectricity could be studied. The bond moment C=O at the center of the core was found to enhance the spontaneous polarization except for one case.

A conducting polymer gel prepared by gamma -ray irradiation and its characteristics

Soluble and fusible poly(3-alkylthiophene) can be transformed into a conducting polymer gel by gamma -ray irradiation. This polymer gel can be processed because it is still fusible. Reversibility of the volume change of this polymer gel has been demonstrated by changing the solvent composition and the temperature and also by doping. The anisotropic shape change of a drawn polymer gel prepared by gamma -ray irradiation has been also demonstrated.

Effect of Hydroxyl Substituent on Ferroelectricity in Ester Type Ferroelectric Liquid Crystals

Abstract A new ester type ferroelectric liquid crystal with hydroxyl substituent on ortho-position of chiral-side phenyl group in core structure has been prepared. The spontaneous polarization of this material is much larger than that of corresponding unsubstituted material. This is interpreted in terms of the effect of intramolecular and intermolecular hydrogen bonds on ferroelectricity in liquid crystal.