Reinosuke Hayakawa

Piezoelectricity and Pyroelectricity of Polymers

This article surveys theoretical and experimental work on piezo- and pyroelectricity of polymers in the 1970s with special emphasis on the origins of these properties. The origins are classified into three types: (A) internal strain (§2), (B) strain- and temperature-dependences of spontaneous polarization (§3), and (C) elastic and/or dielectric heterogeneity of a system with embedded charges (§4). The origin of piezo- and pyroelectricity of poly(vinylidene fluoride) is discussed as a typical example of electret (§5). Piezoelectric relaxations of polymers are discussed in some detail (§6). Methods of measurements of piezo- and pyroelectric constants of polymer films (§7) and applications of polymer films as new transducer materials (§8) are briefly reviewed.

A model theory of piezo- and pyroelectricity of poly(vinylidene fluoride) electret

Abstract Calculation of piezoelectric constants e 31 and e 33 and pyroelectric constant p 3, of poly(vinylidene fluoride) electret is made on the basis of a model theory in which spheres with the spontaneous polarization Psc are embedded in a matrix. Results are in good agreement with observed values of these constants, respectively, when the magnitude of P sc is reasonably assumed. It is to be noted that e31, e32;, e33 and p 3 are interpreted in terms of a unified simple composite model.

Temperature dependence of inclusion-dissociation behavior between molecular nanotubes and linear polymers

We have investigated the inclusion-dissociation behavior between molecular nanotubes and linear polymers in solutions by measuring the induced circular dichroism of the mixture of the molecular nanotubes, which are composed of α-cyclodextrins linked by three cross-linking bridges, and poly(ethylene glycol) modified with azobenzene. It was found that the inclusion complex between the nanotubes and the linear polymers was formed at room temperature, and that the polymers were dissociated from the nanotubes with increasing temperature, as expected theoretically.

Insulation effect of an inclusion complex formed by polyaniline and ?-cyclodextrin in solution

The insulation effect of an inclusion complex formed by polyaniline with emeraldine base as a conducting polymer and β-cyclodextrin as insulators of cyclic form has been studied using the oxidation by iodine in solution of N-methyl-2-pyrrolidone. When polyaniline is oxidized by iodine in the solution, the solution color changes from blue to violet. We observed little change in color at 273 K or a considerable delay of the spectral change at 288 K in the solution of the inclusion complex and iodine in contrast to that in solution of polyaniline and iodine without β-cyclodextrin. This suggests that the conjugated conducting polymer in the inclusion complex is almost completely insulated by the threaded cyclodextrin molecules from the chemical oxidation by iodine and that the oxidation at 288 K proceeds after the inclusion complex dissociates into polyaniline and cyclodextrin in the solution. Copyright

Theory of dynamics of entangled rod‐like polymers by use of a mean‐field Green function formulation. I. Transverse diffusion

A mean‐field Green function theory is developed for investigating the dynamics of entangled rod‐like polymers in solutions. We regard the hindrance of surrounding rods as a multiple (sequential) perturbation to the free transverse or lateral diffusion of a test rod (a rod in consideration) and incorporate the effects of the perturbation elements one by one into the mean‐field Green function. Thus, an explicit expression for the transverse diffusion constant is obtained as a function of a rod length and a polymer concentration for solutions from dilute to semidilute.

New Apparatus for Measuring the Complex Dielectric Constant of a Highly Conductive Material

Difficulties in measuring the contplex dielectric constant of a highly conductive material such as aqueous polyelectrolytes including biopolymers arise from (l) electrode polarization effect and (2) d.c. conductance of the specimen which is very much higher than the conductance due to dielectric loss and drifts with time. A new method has been developed in which the first difficulty is avoided by employing a four-electrode cell and the second orue is overcome by direct measurement of the frequency difference spectrum of specimen impedance, ΔZ(ω)=Z(ω)-Z(ω0), between the measuring frequency ω and the reference ω0. By this procedure, the effect of frequency-independent d.c. conductance is eliminated. With the new method, the frequency range of dielectric measurement is extended from 0.2 Hz to 30 kHz.

Size and number density of precrystalline aggregates in lysozyme crystallization process

Using dynamic light scattering, we investigated supersaturated aqueous solutions of hen egg white lysozyme. We could observe the formation of aggregates only in solutions, from which crystals grew within a few days. The aggregates were grouped into smaller “units” and larger “clusters.” The units consisted of a few molecules, whereas the clusters grew from about 100 nm to 1 μm. At the beginning of aggregation, the number density of the units decreased, while that of the clusters increased. At this stage, unit-cluster aggregation proceeded. At the next stage, the number density of the units became constant, while that of the clusters began to decrease, which means that the units stopped aggregating and cluster-cluster aggregation started. The aggregation mechanism for the clusters fit well with the diffusion limited cluster aggregation model, but this model alone could not explain that the aggregates separated into two groups, corresponding to units and clusters, and that the units stopped aggregating duri...

Experimental Study of Nonlinear Dielectric Relaxation Spectra of Ferroelectric Liquid Crystals in the Smectic C* Phase

Nonlinear dielectric relaxation spectra of two kinds of ferroelectric liquid crystals (FLC) are investigated in the chiral smectic C (SmC*) phase. The linear spectrum shows the relaxation of Debye type and the third-order nonlinear spectrum also shows the relaxation of Debye type generalized to the nonlinear case. The third-order nonlinear dielectric increment is found to be negative, which indicates that the dielectric nonlinearity of FLCs in the SmC* phase mainly originates from the saturation of molecular dipole moments induced by the applied electric field. The profiles of linear and nonlinear spectra remain almost unchanged throughout the SmC* phase. In the vicinity of the SmA-SmC* phase transition temperature, the linear spectrum shows the critical behavior of Curie-Weiss type and the third-order spectrum shows a sharp peak.

Theory on inclusion behavior between cyclodextrin molecules and linear polymer chains in solutions

The inclusion–dissociation behavior in the complex formation between cyclodextrin molecules and linear polymer chains in solution is theoretically investigated by using a lattice model. The cyclodextrins cooperatively include or dissociate the linear polymer chain when the interaction energy between the adjacent cyclodextrins is strong. Copyright

Kinetic study on the early stage of the crystallization process of two forms of lysozyme crystals by photon correlation spectroscopy

By using photon correlation spectroscopy, we have investigated the kinetics of the growth of clusters in two kinds of supersaturated lysozyme solutions at pH 4.6 and temperature 35°C from which orthorhombic rectangular crystals and needle-like crystals appear. Although the two kinds of crystals have quite different final morphologies, the increase of the cluster size in the early stage of the crystallization process can be commonly explained by a diffusion-limited aggregation model, which suggests that the clusters of random aggregates are formed in the early stage irrespective of the crystals systems or habits. We suggest that the needle-like crystals may be what these initial clusters grow to be.