Tomonori Koda

Smectic-A Phase of a Bidisperse System of Parallel Hard Rods and Hard Spheres

A binary system of parallel hard spherocylinders and hard spheres are considered to examine influence of addition of spherical molecules to the pure system of rod-like molecules, especially the influence on the structure of the smectic-A phase. Free energy of the system is calculated through the second virial approximation, and nematic–smectic-A transition is estimated by stability analysis of nematic state with sinusoidal density fluctuation. Constant pressure Monte Carlo simulation is also used to confirm a prediction of the stability analysis which prediction indicates that the addition of spherical molecules induces a smectic-A phase as a microphase separation between the spheres and the spherocylinders.

Phase Diagram of the Nematic-Smectic A Transition of the Binary Mixture of Parallel Hard Cylinders of Different Lengths

We study the nematic-smetic A phase transition of binary mixture of parallel hard cylinders of different lengths. We use the Helmholtz free energy truncated at the second virial term. Changing values of q (length of a longer cylinder), x (composition) and η (packing fraction) of the cylinders, we obtained the transition points at which the nematic phase becomes unstable for a sinusoidal density perturbation. Phase diagrams on η vs x plane are drawn for various q s. Depending on q and x , the stable region of the smetic A is suppressed or enlarged, and two types of structures of the smetic A appear. In one type of the structure,each layer of the smetic A contains longer particles and shorter particles uniformly. In the other type of the structure, layer of shorter particles and layer of longer particles stack alternatively.

Homeotropic orientation of nematic liquid crystals induced by dissolving polypropyleneimine dendrimer having peripheral mesogens

A mixture of nematic liquid crystals (NLCs) with a small amount of a polypropyleneimine-based liquid crystalline dendrimer (D-6PC5 and D-6PPCN) exhibited spontaneous homeotropic alignment between the native glass substrates. This dendrimer-induced homeotropic alignment required two conditions; 1) the dendrimer completely dissolves in the NLC, and 2) a substrate surface is hydrophilic with the surface free energy above approximately 65 mN·m−1. The interdigitated-electrode cells without any surface treatment of the substrates were fabricated by filling with the LC dendrimer (D-6PC5)/nematic LC mixtures. They exhibited an electro-optical behavior when applying AC, vertical-alignment drive occurred in the cells. Based on these results, we speculated that the dendrimer adsorbs on the substrate surface and acts as a vertical alignment layer.

Polarization Reversal in Ferroelectric Fluoro-Polymers.

This paper deals with polarization reversal in single crystalline films of a ferroelectric copolymer of vinylidene fluoride and trifluoroethylene. The activation electric field is about 0.9 GV/m, which is relatively large compared with that for other samples. The process of polarization reversal in the single crystalline films becomes very sharp, and the sharpness is discussed on the basis of the nucleation and growth theory.

Test of Ferroelectricity in Non-stretched Poly(vinylidene fluoride)/Clay Nanocomposites

We measured of the electric displacement D versus electric field E (D–E) hysteresis loop for non-stretched film samples of poly(vinylidene fluoride) (PVDF)/clay nanocomposites. The film was fabricated by compressing melted pellets followed by rapid cooling. The pellets were prepared by melt-compounding method. For the non-stretched film, we obtained clear D–E hysteresis loops that are clear evidence of ferroelectricity at room temperature. Results of X-ray diffraction pattern analysis indicate that the crystal structure of PVDF in PVDF/clay nanocomposites is similar to the β-form of pure PVDF. We conclude that the crystallization of β-form PVDF in PVDF/clay nanocomposites is induced by the epitaxial growth of the β-form on the surface of clay platelets.

Ferroelectric properties and polarization reversal phenomena in nylon 11

Abstract Polarization reversal switching transients of nylon 11 were measured for samples annealed in various conditions. The relation between the ferroelectric properties and hydrogen bonds between main chains is discussed. Polarization reversal of nylon 11 begins by breaking of the hydrogen bonds and ends by linking of them. However, the reason why the spontaneous polarization is difficult to be reversed in well annealed samples of nylon 11 is not because hydrogen bonds are strengthened due to annealing but because packing of molecular chains becomes denser due to annealing.

Theory on the Contribution of Head-Tail Asymmetry of a Molecule to the Phase Transitions in Chiral Smectic Liquid Crystals

A chiral rod-like molecule has the head-tail asymmetry, so that the pair potential between such molecules in head-to-head configuration is naturally different from the potential of those in tail-to-tail or head-to-tail configuration. Taking the head-tail asymmetry into account, we propose a simple model of chiral smectics and calculate the free energy of possible phases in a mean field approximation. The results show that the head-tail asymmetry can contribute to stabilize certain type of antiferroelectric phase between the ferroelectric smectic-C * phase and the antiferroelectric smectic-C * A phase.

Novel method for producing amorphous cellulose only by milling.

The present study investigated a novel method for producing amorphous cellulose by milling without adding water. A new type of milling machine was developed (called a shear and cooling milling machine (SCMM)), which was capable of applying mechanical shear and cooling during the milling process. The SCMM consisted of a pair of mortars attached to a servomotor and a ring cooler. Wide-angle X-ray diffraction (WAXD) analysis was used to determine the cellulose crystallinity in samples produced using the SCMM at different milling temperatures. The results of WAXD for cellulose powder milled at lower temperatures exhibited no diffraction peaks. This experimental result demonstrates that the SCMM produces amorphous cellulose easily by cooled milling without the addition of water. The milling conditions, such as the applied shear and cooling, can be used to control the crystallinity of cellulose.

Synthesis and Characterization of Polypropyleneimine Dendrimers Having Peripheral Mesogenic Groups: Homeotropic Orientation and Mesogen Structure

In order to estimate the effectiveness of mesogenic structure on the spontaneous homeotropic orientation of side-chain type liquid crystalline dendrimers, five mesogens, 4′-methoxybiphenyl (PPO1), 4-methoxyphenyl benzoate (BPO1), trans-4-(4-pentylcyclohexyl)phenyl (PC5), 4′-fluorobiphenyl (PPF), and 3′,4′,5′-trifluorobiphenyl (PPF3), were introduced to the terminal amino groups of a second-generation polypropyleneimine dendrimer. Among them, the PC5 mesogen exhibited superior homeotropic orientation during the slow cooling process from the isotropic melt. Using the PC5 mesogen, the effect of the spacer length (n) was also examined. Homeotropic orientation was observed only for n = 3 and 6, which exhibited a stable smectic A phase in a wide temperature range.

Effect of Addition of Hard Spheres to the Smectic-A Phase of Parallel Hard Spherocylinders

Abstract Constant pressure Monte Carlo simulation is used to discuss the structure of binary mixtures of parallel hard spherocylinders and hard spheres. Results of the simulation indicate that, the smectic layer periodicity is stretched when we add the spheres to the smectic-A phase of the spherocylinders.