Katsufumi Tanaka

The electrorheological property of a polyaniline-coated copolystyrene particle suspension

Polyaniline-coated copoly (styrene styrenesulphonate) (PSS) particles were prepared by oxidative polymerization of aniline hydrochloride using ammonium persulphate in the presence of anionic PSS particles. Polyanilinecoated PSS particles were found to be higher dispersibility than polyaniline itself in an organic solvent. A suspension of polyanilinecoated PSS particle in silicone oil was found to exhibit high performance at higher temperature without the necessity for water.

Electrorheological property of a polyaniline-coated silica suspension

Abstract Silica particles, whose surfaces were completely covered with polyaniline, were prepared by oxidative polymerization of aniline with ammonium persulphate in the presence of silica particles. The electrorheological property of a suspension of polyaniline-coated silica particles dispersed in silicone oil was found to exhibit a high performance even at high temperatures.

Effects of cell parameters on the properties of hybrid twisted nematic displays

This article presents the results of an investigation of the electro-optical response for a hybrid twisted nematic (HTN) liquid crystal display. The device used both a hybrid alignment and a twisted director configuration. In comparison with the conventional twisted nematic mode, a faster response and a smaller operation voltage were obtained by using an appropriate amount of chiral dopant. The characteristics of the HTN cells were dependent on cell parameters such as the chemical nature of the polymer alignment layer, the cell thickness, the set twist angle, and the concentration of chiral dopant. Response times of 1.0 ms for turn-on and 16 ms for turn-off were achieved by the regulation of cell parameters. Computer simulations of the director configuration demonstrated that twist deformation plays an important role in the determination of the response characteristics.

Electrorheological effect of anisotropic solution of poly(γ-benzyl-L-glutamate) induced by stepwise electric fields

The electrorheological (ER) effect of an anisotropic solution of poly(γ-benzyl-L-glutamate)(PBLG) in 1,4-dioxane with a concentration of 15 wt % was measured at a shear rate of 2.6 s -1 by our parallel-plate sliding rheometer. The solution under shear flow was stimulated by stepwise electric fields up to 3.0 kV/mm. Remarkable changes in the beginning of the transient ER response were observed according to the strength of the stepwise electric fields. The lower electric field gave a smaller increase in shear stress depending on the electric-field strength, while the larger electric fields above a critical strength tended to give a larger stress response. The maximum shear stress enhanced by the electric fields in the present experiment was in excess of 10 times the steady shear stress under no electric field. The ER effect was discussed in terms of the Miesowicz viscosities, the interaction among anisotropic domains, as well as the electrohydrodynamic instability.

STRESS BEHAVIOR AND CONDUCTIVITY OF THE ELECTRO- RHEOLOGICAL SUSPENSIONS

The steady stress under static electric fields and the conduction current passing through the electro-rheological (ER) suspensions with cation exchange resin particles were investigated simultaneously as a function of the shear rate. The shear thinning behavior was found for a suspension with a higher viscosity of the continuous phase. Further, a remarkable dip behavior was found for a dilute ER suspension. The apparent conductivity, which was calculated from the conduction current, probed sensitively the corresponding behavior to the stress responses.

SHEARING EFFECTS ON THE ELECTRORHEOLOGICAL RESPONSE

The steady and transient stress responses were investigated from lower shear rates to higher shear rates at a given strength of the electric field, and the individual experimental conditions were reduced to Mason number (Mn). The electro-rheological response was found in the region with higher Mn of the order of 10, and the transient response became faster as the shear rate increased. These results show that the effect of chance of collision among the polarized particles would play an important role even in the region.

Visco-elastic properties of reentrant nematic liquid crystalline mixtures

The visco-elastic properties for binary mixtures of 4-n -hexyloxy-4′-cyanobiphenyl (6OCB) and 4-n-octyloxy-4′-cyanobiphenyl (8OCB) are investigated in detail by a light scattering technique. The mixtures exhibit a reentrant nematic (RN) phase between the smectic A (SmA) and crystal phases in the range 22.0–29.5 wt % of 6OCB. The viscosity and the elastic constant increase with cooling in both the nematic and reentrant nematic phases. It is also found that the mixtures exhibit anomalously large values of viscosity and elastic constant near the phase transition, i.e. a pretransitional phenomenon can be observed. The activation energy for viscosity is smaller in the RN phase than in the ordinary nematic phase appearing at higher temperatures, while the normalized elastic constant (defined as the ratio of the elastic constant to the square of the dielectric anisotropy) is larger. Moreover, the visco-elastic behaviour depends on the specific time during which the sample has been kept in the SmA phase. These results confirm that the SmA phase has a strong influence on the formation of molecular aggregates, which plays an important role in the reentrant phenomenon of these systems.

Electro-optical response of hybrid twisted nematic liquid crystal displays

A novel operating mode for a liquid crystal display device has been developed. The devices involved both hybrid alignment and twisted director configuration. The operating mode was thus termed a hybrid twisted nematic (HTN) mode. In comparison with the conventional twisted nematic mode, faster response and smaller operation voltage have been obtained by using a proper amount of chiral dopant and a homeotropically aligning surfactant having an appropriate length of alkyl chains. The characteristics of the HTN cells were strongly dependent on the chain length and the applied bias voltage. It was also found that a chiral dopant played an important role in the director configuration associated with hybrid twisted alignment.

Liquid Crystalline Alignments on Polar Surfaces Covered with Amino and Hydroxyl Groups

Molecular alignments of three types of liquid crystalline materials on polar solid surfaces have been investigated by the use of polarized optical microscopy. On an amino-coated glass substrate, p ′-alkyl- p -cyanobiphenyls, having one polar cyano group as a terminal moiety, exhibits homeotropic alignment; that is, the molecules align perpendicular to the substrate, whereas p ′-pentyloxy- p -cyanobiphenyl and p -(pentylbenzoic acid)-p-cyanophenyl ester, having two polar groups as a terminal and a spacer, appear to align parallel to the substrate surface. These results indicate that the position and the number of polar groups in a liquid crystalline molecule play an important role in the alignment. On a poly(vinyl alcohol)-covered substrate, which has polar hydroxyl groups, different alignments are observed. It has also been found that the alignments depend on the atmosphere humidity.

Concentration dependences of dielectric properties at 105 Hz and 106 Hz for aqueous solutions of hydroxypropyl cellulose

The concentration dependences of dielectric properties measured at 105 Hz and 106 Hz are reported for aqueous solutions of hydroxypropyl cellulose. Phase behaviour of the solutions was also observed with a polarizing optical microscope. For solutions with concentrations well above 40 wt %, polydomain textures, including the banded texture, were observed after a prehistory of deformation. No significant discontinuous changes in the dielectric constant, εr′, and loss factor, εr″, were found at the concentrations around the onset of the isotropic–cholesteric phase transition and in the biphasic region. In contrast, the steeper changes in εr′ and εr″ were found at the critical concentration for the fully developed cholesteric phase transition with the polydomain textures.