Shigeo Iwayanagi

X-ray structure analysis of trans-1,4-polybutadiene

Abstract The crystal structure of trans-1,4-polybutadiene has been reported by Natta et al. to be pseudo-hexagonal below its solid-phase transition temperature. In the present X-ray structure analysis, it is revealed that the crystal belongs to the monoclinic system with the space group P21/a. The unit cell, with the lattice constants a = 8.63 A, b = 9.11 A, c = 4.83 A, and β = 114°, includes four molecular segments.

Magneto-Orientation of Phospholipids

Abstract Magneto-orientation effects were observed for platelets of thin layered single crystals of L- and DL-dipalmitoylphosphatidylcholine (DPPC), and for single crystals of polyethylene (PE) suspended in xylene. For both L- and DL-DPPC crystals, a biaxial magneto-orientation was observed, in which both directions of hydrocarbon chain and phosphorylcholine group were directed perpendicular to the applied field direction. For PE, the hydrocarbon chain direction was oriented perpendicular to the field. From the orientational behaviour under the magnetic field, the anisotropy of diamagnetic susceptibility, the difference between susceptibilities parallel and perpendicular to the hydrocarbon chain direction, is evaluated as − 9 × 10−8 and − 1 × 10−8 emu/cm3 for L-DPPC and PE, respectively. The origin of the diamagnetic anisotropy of DPPC is briefly discussed in terms of the molecular and crystal structures.

Nuclear Magnetic Resonance Study of Molecular Motion in Polyethylene Crystal

An NMR (nuclear magnetic resonance) study is made on the α or crystalline dispersion of polyethylene which has been found viscoelastically between room temperature and its melting point. Narrowing of NMR absorption line, increase of the mobile fraction and anisotropy of the narrowing are observed in the temperature range of the α dispersion both on melt grown and solution grown specimens. This α narrowing is found to occur at higher temperatures (i.e. the relaxation time is longer) for specimen with thicker crystalline lamella and to be so anisotropic that it disappears when all the molecular axes are aligned parallel to the main magnetic field H0. The experimental results indicate that the molecular motion underlying the crystalline dispersion is the large amplitude torsional oscillation of folded polyethylene chains.

Anomalous Ultrasonic Absorption and Dispersion of Nematic Liquid Crystals near the Clearing Point

The attenuation coefficient of longitudinal ultrasonic waves in the nematic-isotropic phase transition regions of liquid crystals has been measured as a function of both temperature and frequency. A sharp maximum is observed in the attenuation coefficient at the phase transition temperature Tc. The temperature dependence of the velocity has also been measured at 2 MHz, and a sharp minimum is observed at Tc. The anomalous changes of the ultrasonic propagation properties in the nematic phase near Tc are analysed and discussed by a phenomenological treatment based on the Landau-Khalatonikov theory of critical slowing down. On the other hand, behaviors in the isotropic phase near Tc are discussed in terms of the theory proposed recently by Imura and Okano. It is concluded that the anomalies are associated with the nematic-isotropic phase transition which is of first order even though it is nearly of second order.

Lyotropic phase transitions in single crystals of l- and dl-dipalmitoylglycerophosphocholines

Abstract Lyotropic phase transition behaviour of solution-grown mono-domain thin layered crystals of L- and DL-dipalmitoylglycerophosphocholines (dipalmitoyl-GPC) was investigated in a low hydration region at room temperature. X-Ray diffraction measurements and observations by a polarising microscope were performed on the same crystal. In the layer plane of the as-grown thin layered crystal of l - or dl -dipalmitoyl-GPC, which was considered to be dihydrated (phase II), an optical anisotropy was observed. Through a slight absorption of water, the dihydrated crystal showed a monotropic phase transition to a lyotropic mesophase (phase III), in which the optical axis was rotated by about 90° in the plane of the layer. Associated with this phase transition, anisotropic changes both in the unit cell and the crystal dimension occurred. Further absorption of water induced a second lyotropic phase transition for each of the two substances, where the optical anisotropy in the layer plane vanished (phase IV). Combined X-ray measurements suggested that the optical anisotropies observed in phase II and III were caused not only by the inclination of the long aliphatic chains but also by the arrangement of the polar groups of the molecules, and that the binding of water to dipalmitoyl-GPC slightly differed in the l - and dl -molecules in the thin layered crystals and also in as-received powder (phase 1) from as-grown crystals.

Effects of benzyl alcohol on phosphatidylcholine lamellar phase with different water contents

Effects of benzyl alcohol (BA) on the bilayer thickness dl and the fluidity of egg phosphatidylcholine (PC) lamellar phase with various water contents have been studied by X-ray diffraction and the proton spin-lattice relaxation rate. At lower water contents, BA causes dl to decrease and the rate of molecular motions to increase. By contrast, with increasing BA at excess water, dl remains nearly unchanged, though the rate of motions increases. Hydration experiment for egg phosphatidylcholine lamellae with BA at a 1 : 1 molar ratio shows that in the range from 15% to 30% water, dl decreases to the value of the fully hydrated sample without BA and is nearly constant above 30% water. The value at full hydration is suggested to be a lower limit of the bilayer thickness, the chain is in the unperturbed state. It is in an extended structure at lower water contents. This leads to the difference in the effect of BA on the bilayer thickness at different water contents.

Electron diffraction study on single crystals of l-type and dl-type lecithins

An electron diffraction study was carried out on thin single micro-crystals of l-type and dl-type dipalmitoyl lecithins grown in xylene suspensions and fine net patterns were obtained and the mechanism of the thermotropic phase transitions of them was clarified. From the apparent structure of diffraction patterns in low temperature, it is confirmed that the two dimensional lattices have p mm symmetry in l-type and in dl-type lecithins. Lattice parameters from the [001] projection are d100 = 9.9 A and d010 = 8.8 A in l-type, and d100 = 17.2 A and d010 = 8.9 A in dl-type. With anisotropic variation of dimensions along a and b axes, i.e. contraction for a and expansion for b, induced by temperature rise by electron irradiation during the observation, these diffraction patterns of the lattices of l-type and dl-type were transformed into those characterized by the six diffraction spots having nearly the same spacings. Four of them are observed on slightly outer and two are slightly inner positions as compared with their mean spacings of about (4.1 A)−1 in l-type and about (4.2 A)−1 in dl-type. The changes in the patterns observed indicate that at low temperatures the hydrocarbon chains are nearly perpendicular to the layer in dl-type lipid, and tilted with a more complicated packing in l-type ones. The dimension along a in dl-type is twice as large as that in l-type.

Phase Transitions in Single Crystals of L-DPPCand DL-DPPC

Abstract By use of thin layered single micro-crystals obtained from xylene suspensions, the polymorphism of L- and DL-dipalmitoylphosphatidylcholines (DPPC) was studied by electron and X-ray diffractions, microscopic observations, and thermal analyses, with particular attention to the structural transformation in the bilayer plane associated with a thermotropic phase transition, which occurred at about 60°C for dihydrated crystals. At this phase transition, the disappearance of the optical anisotropy in the bilayer plane of the low temperature phase and large changes in crystal dimensions were observed microscopically, and by diffraction studies corresponding changes in unit cell parameters and intensity distributions were observed. The effect of water on thermotropic phase transition behaviours of DPPCs were also examined. The combination of the present experimental methods and the use of monodomain single crystals facilitate the analysis of molecular structures and packings in bilayer plane, which will...

Crystal and Liquid-Crystal Structure of a Disk-like Molecule Triphenylene Hexa-n-Dodecanoate

A disk-like molecule triphenylene 2,3,6,7,10,11-hexa-n-dodecanoate is known for its three columnar mesophases D0, D1, D2 in the order of ascending temperature. X-ray diagrams obtained from oriented specimens show that the plane of triphenylene core of the molecule is not perpendicular to the columnar axis in both D0 and D1 mesophases as well as in the crystalline phase; the hydrocarbon side chains are in a relatively regular array throughout these phases except in the D2 phase. The two-dimensional lattice parameters determined for the array of the columns are different from those reported previously.

Complex Shear Viscosity of Liquid Crystals in the Isotropic Phase of Nematics

Abstract By use of the torsional quartz crystal method, the real and imaginary parts of the complex shear mechanical impedance of several nematogenic materials were measured as functions of the temperature at frequencies ranging from 50 to 150 kHz. From the impedance, we have determined the real and imaginary parts of the complex shear viscosity, in which a remarkable pretransitional anomaly is observed in the isotropic phase near the isotropic-nematic phase transition temperature, T c. In the nematic phase and the isotropic phase except for the vicinity of T c, the Newtonian behaviour is observed. The behaviour of the complex shear viscosity in the isotropic phase has been analyzed by the theory of de Gennes, and it is shown that the observed behaviour can be well described by the theory.