Seiji Taki

FINE STRUCTURE OF THE III-I TRANSITION AND MOLECULAR MOTION IN POLYTETRAFLUOROETHYLENE.

The fine structure in the III-I transition region and the molecular motion of polytetrafluoroethylene under high pressure have been studied by X-ray diffraction and nuclear magnetic resonance. In the transition region from the high pressure phase III to phase I, two kinds of crystals were observed to coexist over a considerably wide temperature range. This fact suggests that the abnormal attenuation of ultrasonic waves reported in this transition region is due to a density fluctuation of these crystals. Also, a detailed study on the molecular chain conformation and the molecular motion in phase I revealed that there exists in the higher temperature region of phase I a new region, where the molecules have apparently a planar zigzag conformation as a result of right-handed and left-handed helical thermal motions in molecular chains.

Change of Temperature and Elastic Stiffness during Dehydration Process of Polyacrylamide Gel

Temporal changes of the weight, volume, temperature and elastic properties during the dehydration process of a polyacrylamide (PAAm) gel were studied. Both the weight and the volume monotonically decreased in the early stage of the process and then tended to saturate in the late stage. At the crossover point between these two dependencies, the temperature of the gel and its elastic stiffness showed anomalies, which indicated similar aspects to the glass transition often observed in non-crystalline polymers. The water content in gels is an important factor affecting the transition.

Variations of Mechanical Properties in Egg White during Gel-to-Glasslike Transition

Simultaneous measurements of weight, volume and mechanical properties have been performed during the gel-to-glasslike transition of heat-treated egg-white gel. Change in the elastic stiffness occurred in three steps: in the initial stage, it remained almost constant, then increased exponentially, and lastly, saturation was attained. The saturation point almost coincided with the characteristic time at which the rates of decrease of the weight and volume changed. In addition, from the time dependence of the differentiated values, the close correlation between the elastic stiffness and weight was revealed. It was also found that the loss of free water induces an increase of about a thousardfold in elastic stiffness of gels during transition.

NMR and Raman Scattering Studies of MBBA and EBBA

Abstract The refined broad line NMR spectra of MBBA and EBBA and the Raman spectra in the low frequency region (100 ∼ 650 cm−1) of EBBA are given. The band associated with the accordion mode vibration of the end butyl chain of these molecules is assigned to 280 cm−1 in Raman spectrum. The analysis of accordion mode vibration indicate that the end butyl chain EBBA molecule tends to take all trans conformation, and that that of MBBA molecule tends to take the conformation which has constraint, such as gauche conformation. Assuming that the whole molecular conformation of each sample in the nematic phase, assignments between protons attached to each molecule and each line in the NMR spectrum are given. Molecular and segmental motions, molecular packing, and orientational order in the nematic phase of these samples are discussed.

Systematic Study of Odd-Even Effect in Molecular Alignments of Cyanobiphenyl Liquid Crystals with Scanning Tunneling Microscope. I. Experimental Observation

Systematic observations are carried out for molecular alignments of monolayers of homologous series in cyanobiphenyle (CB) liquid crystals such as 6CB to 12CB on highly oriented pyrolytic graphite (HOPG) substrates using a scanning tunneling microscope. For 6CB the molecular alignments are also observed on molybdenum disulfide substrates (MoS 2 ) as well as HOPG. In 6CB monolayers, the characteristic structures indicating both properties of a single and double row previously reported are observed. In 7CB, 9CB and 11CB monolayers only the single row property is observed. The monolayer alignments of 8CB, 10CB and 12CB show on the other hand double row characteristics. Thus all the observed aspects clearly indicate the odd-even effect of carbon numbers in an alkyl chain. The morphology of molecular alignments due to the odd-even effect in monolayers of cyanobiphenyl liquid crystals on HOPG are systematically determined. Based on the experimental observation a qualitative model on the molecular alignments of ...

Direct observation of the growth process of organic crystals by scanning tunnelling microscopy

Abstract STM (scanning tunnelling microscope) observation was conducted on n-paraffin molecules (n-C 33 H 68 ) adsorbed on a graphite substrate. A series of the STM images could reveal each of the progressive stages of the crystal growth, suggesting how the molecules grow into two-dimensional crystals.

Ultrasonic Study of High Pressure Phase in Polyethylene

Behaviors of transitions and the nature of high pressure phase in polyethylene are studied using methods of longitudinal and transverse ultrasonic waves, differential thermal analysis (DTA) and X-ray diffraction by PSPC X-ray system. Two anomalous absorption peaks of longitudinal wave agree with the normal phase to high pressure phase transition temperature and the high pressure phase to fused phase transition temperature as observed by DTA and X-ray diffraction, respectively. For the folded-chain crystal sample, the recrystallization phenomena by lamella thickening during the heating process has been discovered by the anomaly in longitudinal sound velocity. The result of transverse wave shows that the modulus of rigidity of high pressure phase is of the same order in magnitude as that of the fused state. Therefore, the high pressure phase should be a nematic liquid crystal-like state.

Pressure Effect on Ferroelectric Phase Transition of Vinylidene Fluoride-Trifluoroethylene Copolymer (54/46 mol%)

Pressure effects on the ferroelectric phase transition of a vinylidene fluoride-trifluoroethylene (VDF-TrFE) copolymer with 54 mol% VDF content have been investigated by means of DTA and X-ray diffraction methods up to 400 MPa. At high pressures above 200 MPa this copolymer exhibited multiple DTA peaks upon a ferro-to-paraelectric phase transition and a temperature hysteresis in the transition points. Correspondingly, the results of high pressure X-ray diffraction measurements showed the singular temperature variation of (200, 110) reflections, suggesting the pressure-induced structural transformation.

Density Variation in Heat- and Pressure-Treated Egg White during Gel-to-Glass-like Transition

Simultaneous measurements of the area (volume) and mass change were carried out in heat- and pressure-treated egg white during the process of the gel-to-glass-like state transition. The calculated density of these two specimens showed quite different time variations; the density of the heat-treated specimen remained almost constant, while that of the pressure-treated one changed considerably. Moreover, the scanning electron microscopy observations revealed that the surface structure of the pressure-treated gel is larger and more coarse than that of the heat-treated one, suggesting a close relationship between the structures of the two gels and the changes in the density during the gel-to-glass-like state transition. The differences in the microscopic structures in these two gels were also elucidated by X-ray diffraction measurements.

Molecular Alignment in Monolayer of n-Alkyloxy-Cyanobiphenyl and Clear Evidence of the Odd-Even Effect

Systematic observations are carried out to determine molecular alignments of monolayers of homologous series in n-alkyloxy-cyanobiphenyl (nOCB) liquid crystals in the range of n=7 to 10 on both molybdenum disulfide (MoS2) and highly oriented pyroritic graphite (HOPG) substrates using a scanning tunneling microscope. Our observations determined the following. For odd n of carbon atoms in alkylchains such as 7OCB and 9OCB, the molecular alignments on both substrates (MoS2 and HOPG) are mainly due to the interaction between alkylchains and substrates. For even n, on the other hand, the alignments are basically due to the dipole-dipole interaction between liquid crystal molecules on the substrates. These differences occur due to the situation of the end-carbon in an alkylchain. However, 10OCB on HOPG shows an exceptional alignment resulting from the alkylchain-length effect. Excluding this case, all other seven combinations clearly indicate the odd–even effect. The validity of our previous model for molecular alignments of nCB monolayers has been confirmed for nOCB.