Kohji Tashiro

THEORETICAL EVALUATION OF THREE-DIMENSIONAL ELASTIC CONSTANTS OF NATIVE AND REGENERATED CELLULOSES : ROLE OF HYDROGEN BONDS

Three-dimensional elastic constants were calculated for cellulose crystalline forms I and II (native and regenerated celluloses, respectively). The calculated Youngs modulus El along the chain axis is 167.5 GPa for form I and 162.1 GPa for form II. The El of form II has only a slightly lower value than that for form I. This is consistent with the X-ray data (c. 120–140 GPa for form I and c. 110 GPa for form II) although the absolute values are large. The El was found not to be affected by intermolecular interactions but by intramolecular hydrogen bonds along the chain axis, especially the bond between the hydroxyl side group and the ether oxygen atom of the glucose ring (type a). A calculation neglecting this hydrogen bond gives the largely reduced El of c. 70 GPa. Anisotropy of the Youngs modulus and linear compressibility in the planes perpendicular to the molecular chain axis were also calculated. In the form I crystal, where the hydrogen-bonded sheet planes are stacked together by non-bonded van der Waals interactions, the modulus is large within the sheet plane and small in the direction perpendicular to the sheet: the anisotropy is similar to that reported for the nylon 6 α and γ forms. In form II the modulus is large but the anisotropy is not so remarkable, which is similar to atactic poly(vinyl alcohol) and poly(m-phenylene isophthalamide). The same tendency is seen also for the linear compressibility. In parallel with the calculation of the elastic constants, the lattice vibrational frequencies were calculated for forms I and II and compared with the observed infra-red and Raman spectral data so as to confirm whether the force fields used were reasonable.

Structural study on ferroelectric phase transition of vinylidene fluoride-trifluoroethylene copolymers (III) dependence of transitional behavior on VDF molar content

Abstract Structural changes occurring in the ferroelectric phase transition of vinylidene fluoride-trifluoroethylene (VDF-TrFE) copolymers with the various VDF molar contents have been investigated by means of X-ray diffraction and infrared spectroscopic methods. The phase transition occurs among three crystal phases of the low-temperature (regular all-trans conformation), the high-temperature (gauche conformation with a large rotational motion), and the cooled phases (disordered trans conformation). In the copolymer with low VDF molar content less than 40%, the broad transition between the cooled phase and the high-temperature phase is observed and the conformational change from trans to gauche is not so perfect. In the range of VDF 50–60%, the transition becomes more definite, and on the way of heating the low-temperature phase transforms to the cooled phase, which transfers continuously to the high-temperature phase. For copolymers of VDF 70–80%, a clear and discontinuous first order transition between...

Structural phase transition in ferroelectric fluorine polymers: X-ray diffraction and infrared/Raman spectroscopic study

Abstract The structural phase transition has been investigated by X-ray diffraction and infrared and Raman spectroscopic measurements for ferroelectric fluorine polymers, including poly(vinylidene fluoride) and its copolymers with trifluoroethylene or tetrafluoroethylene. One of the most characteristic features of this ferroelectric transition is the large conformational change of the molecular chains between the trans and gauche rotational isomers, quite different from the structural change observed generally in the usual ionic ferroelectric materials. The crystallization and transition behaviors depend sensitively on the monomer composition in the copolymers as well as on the sample preparation conditions. The roles of the optic and acoustic phonons in the ferroelectric phase transition have been discussed based on the temperature dependences of the far-infrared spectra and the ultrasonic velocity.

Structure and piezoelectricity of poly(vinylidene fluoride)

Abstract A theoretical equation for calculating piezoelectric constants (dij) of polymer crystals has been derived and applied to poly(vinylidene fluoride) form 1. The calculated d 33 = -2.5 × 10−11 C/N, is in good agreement with the value of -2 × 10−11 C/N measured by the x-ray method. The calculated d 31, -0.025 × 10−11 C/N, is smaller by two digits than d 33, consistent with the experimental result that the x-ray (002) spot was not shifted nearly as much by the application of the electrostatic field as in the case of d 33 The macroscopic piezoelectric constants d M 31 and d M 33 have been estimated by using a model where the piezoelectric crystal form 1 is embedded in the nonpiezoelectric amorphous matrix; d M 31 = 0.6 × 10−11 C/N and d: = -1.4 × 10−11 C/N at room temperature and d M 31 = 6.8 × 10−13 C/N and d M 33 = -0.5 × 10−11 C/N below the glass transition temperature (Tg ), respectively. These are in the same order as the values observed both at room temperature and below Tg . In the present estim...

Structure and ferroelectric phase transition of vinylidene fluoride-trifluoroethylene copolymers: 2. VDF 55% copolymer

Abstract Molecular and crystal structure changes in ferroelectric phase transition of vinylidene fluoride-trifluoroethylene (VDF-TrFE) copolymer with a VDF content of 55 mol% have been investigated by X-ray diffraction and infra-red and Raman spectroscopy. As the temperature rises from room temperature to the Curie point of ∼60°C, the polar low-temperature phase consisting of all-trans chains experiences a first-order transition to the phase of tilted long trans segments connected by some skew bonds. At higher temperature this new phase transforms continuously and steeply to the non-polar high-temperature phase, where the molecular structure consists of a random combination of TG, TḠ, T3G and T 3 G rotational sequences. In the cooling process the high-temperature phase transforms to the cooled phase, which is essentially equivalent to the phase appearing intermediately in the heating process from the low-temperature to the high-temperature phase. The cooled phase gives a tilting X-ray fibre diagram and is found by X-ray analysis to contain an appreciable amount of so-called 60° domain structure. These are well interpreted by a conformational model of tilting trans structure containing skew linkages. The tensile stress along the fibre axis causes the transformation from the cooled phase to the low-temperature phase, where the probability of 60° domain structure and the degree of chain tilting are remarkably reduced.

Morphological effect on the Raman frequency shift induced by tensile stress applied to crystalline polyoxymethylene and polyethylene: spectroscopic support for the idea of an inhomogeneous stress distribution in polymer material

A tensile-stress-induced low-frequency shift was measured for the Raman bands of crystalline polyoxymethylene (POM) and polyethylene (PE) with different draw ratios λ. The apparent frequency-shift factor p (= ΔvΔσbulk) for the 539 cm−1 skeletal bending mode δ (COC) was found to become larger for the POM sample with lower λ: p = −24 cm−1/GPa (λ = 7), −19 (λ = 17) and −11 (λ = 34). Such a difference in p was too small to detect for the skeletal stretching modes of PE samples with λ = 7 to 100: p = −6.0 cm−1/GPa for vas (CC) at 1064 cm−1 and −4.5 for vs (CC) at 1131 cm−1. This experimental fact, i.e. the dependence of the frequency-shift factor p on sample morphology, cannot be reasonably explained in terms of a homogeneous stress distribution or the simple mechanical series model of crystalline and amorphous phases. Based on the complex mechanical model (i.e. the parallel-series and series-parallel models), the Raman shift could be understood quantitatively, and the intrinsic shift factor α of the crystalline region was estimated as −11 cm−1/GPa for the δ (COC) mode of POM and as −5.0 cm−1/GPa for vas (CC) and −3.8 cm−1/GPa for vs (CC) of PE. A change in the Raman band profile under tensile stress was simulated and compared with the observed data.

Phase transition at a temperature immediately below the melting point of poly(vinylidene fluoride) from I: A proposition for the ferroelectric Curie point

Abstract A phase transition at a temperature immediately below the melting point of poly(vinylidene fluoride) form I has been found by means of differential scanning calorimetry (d.s.c.) and infra-red (i.r.) vibrational spectroscopy. An endothermic d.s.c. shoulder has been observed at a temperature about 10°C below the melting point, in the vicinity of which the i.r. crystalline trans bands decrease in intensity steeply and the crystalline gauche bands increase in intensity, indicating the conformational change from all- trans to T 3 GT 3 G type. These observations have been found to be detectable more clearly for samples subjected to the poling treatment under a d.c. high voltage. The transition shows the characteristic behaviour essentially identical to those observed for ferroelectric copolymers of vinylidene fluoride and trifluoroethylene, except for the irreversibility of the structural change, suggesting that the phase transformation revealed here may be a ferroelectric-to-paraelectric phase transition of polar form I crystal and the the Curie point may be about 172°C. It is consistent with Micherons measurement of the temperature dependence of the dielectric constant. Other structural changes in the form I sample occurring in the temperature range from 20° to 170°C have also been discussed based on the i.r. spectral measurements.

Structural change in the Brill transition of Nylon m/n (2) conformational disordering as viewed from the temperature-dependent infrared spectral measurements

Abstract The structural changes in the Brill transition of aliphatic Nylons m / n have been investigated by carrying out the temperature-dependent infrared spectral measurement for Nylon 6/10 –[–NH–(CH 2 ) 6 –NHCO–(CH 2 ) 8 –CO–] n –, Nylon 6/12 –[–NH–(CH 2 ) 6 –NHCO–(CH 2 ) 10 –CO–] n – and Nylon 10/10 –[–NH–(CH 2 ) 10 –NHCO–(CH 2 ) 8 –CO–] n –. They took the crystal structure of α-form at room temperature. By heating the samples up to the Brill transition temperature region, the conformation of the methylene segments was found to change remarkably from the all trans -zigzag form to the disordered conformation constructed by shorter trans -zigzag segments combined with some gauche bonds. At the same time, the twisting motion was found to occur around the CH 2 –amide bonds. During this order-to-disorder transition of molecular conformation, the intermolecular hydrogen bonds were kept alive although they were weaker gradually with increasing temperature. The methylene segments sandwiched by NH groups [NH(CH 2 ) m NH] were found to be disordered more remarkably than those of CO(CH 2 ) n CO sequence due to the difference in torsional energy barriers around the CH 2 –NH and CH 2 –CO bonds.

Structural changes in non-isothermal crystallization process of melt-cooled polyoxymethylene[II] evolution of lamellar stacking structure derived from SAXS and WAXS data analysis

Structural change occurring in the cooling process of polyoxymethylene from the molten state has been investigated by carrying out the temperature dependent measurements of small-angle X-ray scattering (SAXS) and wide-angle X-ray scattering (WAXS). In the SAXS experiment the generation of lamellar stacking structure with long period of ca. 14 nm was detected at first and then the new lamellae were inserted in between the already-existing lamellae to give the long period of 7 nm below 140 °C. The SAXS data were analyzed on the basis of lamellar insertion model by taking into account the second kind of paracrystalline disorder about the lamellar stacking mode. The thus obtained results were combined with the previously published infrared spectral data, and the structural change was deduced concretely. The generation of taut tie chains passing through the adjacent lamellae was proposed, which could reasonably explain the observation of infrared bands characteristic of extended-chain-crystal-like morphology.

Annealing effect on the ferroelectric phase transition behavior and domain structure of vinylidene fluoride (VDF)-trifluoroethylene copolymers : a comparison between uniaxially oriented VDF 73 and 65% copolymers

Abstract The structure and ferroelectric phase transition behavior were investigated for heat-treated samples of vinylidene fluoride–trifluoroethylene (VDF–TrFE) copolymers with 73 and 65% VDF molar contents. The temperature of the transition from the ferroelectric to the paraelectric phases increased when the samples were annealed in the temperature region of the above phase transition. The domain size, evaluated from the integrated width of the X-ray reflections, also increased drastically at these annealing temperatures. As the annealing temperature increased above the transition point, the resulting sample showed a reduction of the transition temperature. In this case, the domain size decreased slightly and the trans sequential length in the crystalline domain decreased, corresponding to structural disorder due to the invasion of gauche bonds into the trans zigzag chains. In the case of the 65% VDF sample, annealing in the phase transition temperature region resulted in a tilting phenomenon of chains in the crystalline region, but this phenomenon was not detected for the 73% VDF sample.