Yukinobu Murata

Ferroelectric Properties in Polyamides of m-Xylylenediamine and Dicarboxylic Acids

The relationship between electric displacement D and electric field E was studied for polyamides consisting of m-xylylenediamine and aliphatic dicarboxylic acids with numbers of carbon atoms from 6 to 11 and 13. Regardless of the number of carbon atoms in the acids, quenched samples of these polyamides exhibit a D-E hysteresis loop with remanent polarization of 23-67 mCm-2. Polarization is related to the amide groups aligned by the electric field.

Dielectric Hysteresis Loop in Alicyclic and Aromatic Polyamides

The relationship between electric displacement D and electric field E was studied for alicyclic polyamides of 1,3-bis(aminomethyl)cyclohexane and adipic, pimelic and sebacic acids, an aromatic polyamide prepared from hexamethylenediamine (HMD) and isophthalic acid and a copolyamide of HMD with isophthalic and terephthalic acids. Quenched samples of these polyamides were poorly crystalline or amorphous and exhibited a D-E hysteresis loop with the remanent polarization of 26 to 38 mCm-2. The remanent polarizations disappeared at the glass transition temperature of each sample. The origin of the D-E hysteresis loop is attributable to amide groups in amorphous regions.

Dielectric behavior of copolymers of vinylidene fluoride and tetrafluoroethylene

Abstract Dielectric behavior and related bulk properties have been studied on copolymers of vinylidene fluoride (VDF) and tetra-fluoroethylene (TFE) with TFE contents of 10 to 30 mol-%, Dielectric properties of copolymers did not vary much with TFE contents. Copolymers exhibited the dielectric relaxation similar to that as found for poly(vinylidene fluoride) (PVDF) at low temperature which was connected with micro-Brownian motions of the molecular chain backbone in amorphous regions. Variation of the relaxation frequency with temperature in the vicinity of the glass transition was fitted by the modified WLF equation. No noticeable dielectric loss peak associated with the relaxation in crystalline regions in form I1 of PVDF was found at high temperature. This may be understood because the VDF-TFE copolymer has the same structure as form I of PVDF. The dielectric constant and loss increased with increasing temperature and/or decreasing frequency above room temperature owing to the space charge polarization ...

Ferroelectric behavior in polyamides of m-xylylenediamine and dicarboxylic acids

The ferroelectric properties were studied for polyamides consisting of m-xylylenediamine (MXD) and aliphatic dicarboxylic acids with the number of carbon atoms n=6 to 11, which were designated as nylon MXDn. Quenched samples of these polyamides exhibited the ferroelectric hysteresis loop with the remanent polarization P r of 25-67 mCm-2 which decreased with increasing n. Strip-biaxial and biaxial drawing of nylon MXD6 caused the preferential orientation of molecular chains parallel to the direction of drawing and to the film surface, respectively, and increased the value of P r. A reversible pyroelectric coefficient of 4 to 12 µCm-2K-1 was observed for nylons MXD6 and MXD7. The polarization was depolarized with increasing temperature and vanished at the glass transition temperature of the respective samples. The ferroelectricity of nylon MXDn is related to the amide groups aligned by the electric field in amorphous regions.

Polarized infrared spectra of poled aromatic polyamide films

In connection with ferroelectric behavior of aromatic polyamides poled at a high electric field, polarized infrared spectra were studied in poled films of crystalline and amorphous aromatic polyamides consisting of ring systems to elucidate the relation between the orientation of polar groups and the ferroelectric polarization. The infrared spectra revealed that the CO and NH bonds oriented preferably along the poling direction in both crystalline and amorphous polyamides. The crystallinity of the crystalline polyamide increased with poling. In the amorphous polyamide, strong intermolecular hydrogen bonding is closely related to the retention of ferroelectric polarization in the frozen state of molecular motions below the glass transition temperature.

Pressure Dependence of Ferroelectric Transition and Anomaly in Bulk Modulus in Copolymer of Vinylidende Fluoride and Trifluoroethylene

Thermal expansion of copolymer of 52.8 mol-% vinylidene fluoride and 47.2 mol-% trifluoroethylene under varied hydrostratic pressure p up to 100 MPa was observed over a temperature range of 30 to 110°C. Pressure dependence of the ferroelectric transition Tt was evaluated as 0.318 K MPa-1 from the abrupt change in thermal expansion at the transition. This considerably large value of dTt/dp was in good agreement with that found in the dielectric measurements. The bulk modulus vs temperature curve exhibited a conspicuous minimum at the transition of 337 K as is the case with ferroelectric crystals.

Curie transition in poled and unpoled copolymer of vinylidene fluoride and tetrafluoroethylene.

Copolymers of vinylidene fluoride (VDF) and tetrafluoroethylene (TeFE) with TeFE content ranging from 17.8 to 30.7 mol% were studied by thermal, dynamic mechanical, and thermally stimulated current measurements. Below the melting point, a small endotherm was observed in differential thermal analysis. Corresponding to the endotherm, a crystalline relaxation, designated as Tt, was observed by mechanical measurements. It was inferred that the endotherm and the Tt mechanical relaxation were due to the Curie transition. The Curie points of these copolymers were about 50 K lower than those of VDF-trifluoroethylene (TrFE) copolymers with the same VDF content. In X-ray measurements, it was confirmed that these copolymers took the all-trans crystal structure similar to that of PVDF form I of which the crystal lattice expanded in a- and b-axis directions and was disordered in the c-axis repeat in comparison with that for VDF-TrFE copolymers. The Curie temperature for poled samples increased by about 50 K. The poling procedure made the crystal lattice compact in a- and b-axis directions and the c-axis repeat regular; this seems to be related to the considerable increase in the Curie temperature.

Dielectric Properties in Polyamides of m-Xylylenediamine and Dicarboxylic Acids

Dielectric properties were investigated for polyamides consisting of m-xylylenediamine and aliphatic dicarboxylic acids with the number of carbon atoms from 6 to 11, over a frequency range of 25 Hz to 1 MHz, at temperatures from 200 to 400 K. The α relaxation with a relaxation strength of 60 to 80 was observed at temperatures above the glass transition temperature Tg in quenched amorphous samples and was related to the micro-Brownian motion of the molecular chains of these aromatic polyamides. The dipole moment per repeating unit was 9 to 11 D for the α relaxation. The β relaxation observed at temperatures below room temperature exhibited a small relaxation strength, which was attributed to the motion of carbonyl groups with water molecules bound by a hydrogen bond. The space-charge polarization effects took place at high temperatures and low frequencies. The crystallization occurring during the heating process decreased the dielectric constant and loss in the α relaxation and the space-charge polarization.

Effect of hydrostatic pressure on polarization reversal in copolymers of vinylidene fluoride and trifluoroethylene

Polarization reversal in copolymers of vinylidene fluoride (VDF) and trifluoroethylene (TrFE) with intermediate and higher TrFE content is characterized by two polarization current peaks at different electric field intensities. The current peaks at higher and lower field, Eh and El, correspond to polarization and depolarization processes, respectively. The temperature Tl at which El reduced to zero was related to a transition between slightly different phases. The effect of hydrostatic pressure on polarization processes was examined for the copolymers in a low pressure region of 0.1 to 100 MPa. Increasing pressure gave rise to a considerable effect on Eh and El, being similar to that in decreasing temperature. Pressure dependence of the temperature Tl was as large as about 0.3 KMPa-l. This work presents another feature of the polarization processes in these copolymers which are different from those in high VDF content copolymers.

Pressure Dependence of the Ferroelectric Transition in Copolymers of Vinylidene Fluoride and Trifluoroethylene

Effect of the hydrostatic pressure p on the ferroelectric transition Tt in copolymers of vinylidene fluoride VDF and trifluoroethylene TrFE with 47.2 and 35.4 mol-% TrFE has been investigated for dielectric behavior and thermal expansion. The permittivity peak and the abrupt increase in thermal expansion at the transition shifted markedly to higher temperature with increasing pressure. The pressure dependence of the transition dTt/dp observed was 0.31 KMPa-1 on heating for 47.2 mol-% TrFE copolymer and 0.38 KMPa-1 on heating and 0.40 KMPa-1 on cooling for 35.4 mol-% TrFE Copolymer. These values of dTt/dp were consistent with those calculated by the Clausius-Clapeyron relation. The bulk modulus evaluated from the expansion vs pressure curve exhibited a conspicuous minimum at the ferroelectric transition as found for other physical properties.