Munehiro Date

Ferroelectric Behavior in the Copolymer of Vinylidenefluoride and Trifluoroethylene

The linear and nonlinear dielectrical and depolarization processes of the copolymer of vinylidene fluoride and trifluoroethylene have been measured. The D vs. E hysteresis loop below room temperature indicates the ferroelectricity of this copolymer. The dielectric anomaly and the disappearance of remnant polarization at T0=70°C suggest that T0 is the phase transition temperature from the ferroelectricity to the paraelectricity phase. Results are analyzed on the basis of Weiss-type semimolecular theory.

Measurements of nonlinear dielectricity in ferroelectric polymers

Experimental procedures and exemplifying results are described in relation to a nonlinear dielectric investigation of ferroelectric polymers. The apparatus developed here was used to apply a sinusoidal electric field and to detect fundamental and higher harmonic electric displacements with a 0.01% accuracy by means of digital sampling and Fourier transform techniques. Three types of experiments were made for PVDF. Measurements at relatively low fields determined the nonlinear dielectric constants in that the second-order constant was shown to reflect the polarity of the sample and the third order one was positive being consistent with cooperative dipoles. The ferroelectric hysteresis loops obtained at very high fields were analyzed in terms of the higher-order Fourier coefficients. The use of a double frequency wave determined the field-dependent linear dielectric constants which showed a maximum during polarization reversal.

Crystalline phase transition in the copolymer of vinylidenefluoride and trifluoroethylene

The measurement of the temperature dependence of elastic, dielectric, and piezoelectric constants for the film of 55/45% VDF‐TrFE copolymer suggests that the Curie temperature exists at about 70 °C. The lattice spacing sharply changes at a temperature range from 55 to 75 °C. The remanent polarization is also determined from the D versus E hysteresis loop below 75 °C. It is found that the spontaneous strain in crystal lattice is linearly related to the square of remanent polarization. The transition is ascribed to electrostriction due to dipolar orientation.

Large Dielectric Relaxations in an Alternate Copolymer of Vinylidene Cyanide and Vinyl Acetate

An alternate copolymer of vinylidene cyanide and vinyl acetate has been investigated dielectrically at temperatures above Tg ~170°C. A remarkable relaxation was observed in the 1 Hz to 10 kHz frequency range due to a separation from coexisting contributions as a result of the dc conductivity. The relaxation time depends upon the temperature in the WLF according to the characteristics of the micro-Brownian motions of molecular segments. The relaxation strength was found to reach 125, resulting in an unusually high dielectric constant. Such a large relaxation strength is an indication of some cooperative effects in relation to dipolar motions. Cooling to below Tg in the presence of a high electric field creates a large remanent polarization which is consistent with the strong piezoelectric activity reported for this copolymer.

Dielectric hysteresis and rotation of dipoles in polyvinylidene fluoride

Hysteresis curves of the linear dielectric constant, the electric displacement, and the IR absorbance at 1273 cm−1 were observed at −5 °C for a stretched film of polyvinylidene fluoride. The hysteretic polarization was obtained by subtracting the linear electric displacement from the observed electric displacement. Correspondence between hysteretic polarization during the cyclic application of electric field suggests that both originate from rotation of CF2 dipoles in form‐I crystals.

Switching process in composite systems of PZT ceramics and polymers

Abstract The poling process in composite systems of ferroelectric PZT ceramics with a vinylidene fluoride/trifluoroethylene copolymer has been investigated by the time-domain measurements of the switching transients. The bilayer composite undergoes complete polarization reversal, although the switching time is much larger than in pure PZT. The dispersion of PZT particles in the copolymer matrix shows obscured switching transients, but polarization reversal is confirmed by reversal of piezoelectric activity. Since the dielectric constant of the copolymer is much lower than that of PZT, the applied field is greatly reduced in the PZT phase to disable instantaneous polarization reversal. However, the internal field is gradually increased with time to reach the coercive field by accumulation of real charges at the phase boundary due to the dc conductivity in the polymer phase. The conductivity also limits the switching rate to result in a long switching time. The calculated switching curve shows good agreemen...

A new rheological method to measure fluidity change of blood during coagulation: application to in vitro evaluation of anticoagulability of artificial materials

In order to attempt in vitro evaluation of antithrombogenecity for materials of artificial blood vessel tube, a new type of rheometer was developed. The rheometer originally consists of a cylindrical tube suspended from a torsion wire and filled with blood. The tube is excited in torsional oscillation and subsequent damped oscillation is observed. The apparatus can sensitively follow the change of fluidity during coagulation of blood. The damped oscillation curves during coagulation for fibrinogen - thrombin solution and blood put in a cylindrical tube made of the artificial material were measured. For fibrinogen - thrombin solution with lower fibrinogen and thrombin concentrations, the values of logarithmic damping factor (LDF) during coagulation increased and then decreased through a maximum. For blood and fibrinogen-thrombin solution with the higher concentrations of fibrinogen and thrombin, LDF monotonously decreased with the progress of coagulation. With a glass tube, the decrease of LDF for whole blood taken without anticoagulant rapidly occurred within about 15 min after sampling, while, with expanded polytetrafluoroethylene (EPTFE; Goar tex) and polydimethylsiloxane (Silastic) tubes, the decrease of LDF proceeds over 40-60 min. The present method is probably available for in vitro evaluation of anticoagulability or antithrombogenecity of artificial materials.

Microactuators with Piezoelectric Polylactic Acid Fibers—Toward the Realization of Tweezers for Biological Cells

The poly-L-lactic acid (PLLA) shows a high shear piezoelectric constant. We fabricated PLLA fiber samples with large degree of crystallinity and high orientation of crystallites using high-speed spinning. If the electric field is applied to the PLLA fiber in the direction perpendicular to the PLLA fiber axis, the PLLA fiber must be driven by the piezoelectric effect. Therefore, we devised an effective method of applying the electric field to the PLLA fiber. We also developed equipment for measuring the piezoelectric motion of the PLLA fiber, which uses a CCD camera and divided photodiodes. As a result, we could drive the PLLA fiber by the shear piezoelectric effect under the application of ac voltage, and observed the bending motion of the entire PLLA fiber. Finally, we attempted to release and grasp the bead sample using a pair of PLLA fibers like tweezers, and succeeded.

Analysis of a Newly Developed Damped-Oscillation Rheometer: Newtonian Liquid

The behavior of a newly developed damped-oscillation rheometer was analyzed for Newtonian liquids from both theoretical and experimental points of view. This rheometer consists, essentially, of a cylindrical tube suspended from a torsion wire that is filled with the liquid to be tested. In order to determine the relationship between the rheological parameters of the liquid and the period or the logarithmic damping factor measured by this rheometer, a Newtonian liquid was considered as a first test liquid. Based on various assumptions, the equations of motion for the liquid and the cylindrical tube were solved simultaneously. Numerical solutions and approximate analytical solutions valid for certain ranges of the parameters were obtained. The results are compared with experimental results which we measured using this rheometer.

Novel Tweezers for Biological Cells Using Piezoelectric Polylactic Acid Fibers

Abstract We fabricated poly-L-lactic acid (PLLA) fiber samples using high-speed spinning in order to improve their piezoelectricity. If an electric field is applied to the PLLA fiber in the direction perpendicular to its fiber axis, the PLLA fiber must be driven by the piezoelectric effect. We developed an effective method of applying an electric field to the PLLA fiber. As a result, we could drive the PLLA fiber by the shear piezoelectric effect under the application of ac voltage, and observed the bending motion of the entire PLLA fiber. Next, we have designed tweezers using a pair of PLLA fibers controlled by applied ac voltage, and have pursued the realization of PLLA fiber tweezers; finally, this was achived. On the basis of our experimental results, we believe that there is a high possibility of realizing the PLLA fiber tweezers for the manipulation of soft and minute samples such as biological cells.