No abstract

Electrets of carnauba wax and resin have exhibited good stability of trapped charges for nearly 50 years. Dipolar orientation and trapped charge are two mechanisms contributing to the pyro-, piezo-, and ferroelectricity of polymers. Since the 1950s, shear piezoelectricity was investigated in polymers of biological origin (such as cellulose and collagen) as well as synthetic optically active polymers (such as polyamides and polylactic acids). Since the discovery of piezoelectricity in poled polyvinylidene fluoride (PVDF) in 1969, the pyro-, piezo-, and ferroelectricity were widely investigated in a number of polar polymers, such as copolymers of vinylidene fluoride and trifluoroethylene, copolymers of vinylcyanide and vinylacetate, and nylons. Recent studies involve submicron films of aromatic and aliphatic polyureas prepared by vapor deposition polymerization in vacuum and the piezoelectricity of polyurethane produced by the coupling of electrostriction and bias electric fields. Gramophone pickups using a piece of bone or tendon were demonstrated in 1959. Microphones using a stretched film of polymethyl glutamate were reported in 1968. Ultrasonic transducers using elongated and poled films of PVDF were demonstrated in 1972. Headphones and tweeters using PVDF were marketed in 1975. Hydrophones and various electromechanical devices utilizing PVDP and its copolymers have been developed during the past 30 years. This paper briefly reviews the history and recent progress in piezoelectric polymers.

Unexpected crossover dynamics of single polymer in a corrugated tube J. Chem. Phys. 137, 114902 (2012) Nonequilibrium polymer chains induced by conformational transitions in densely interfacial layers J. Chem. Phys. 137, 104903 (2012) Structural and dielectric properties of poly(vinylidene fluoride)-based terpolymer/copolymer blends developed on aluminum foil J. Appl. Phys. 112, 053505 (2012) Particle size dependence of resonant-tunneling effect induced by CdS nanoparticles in a poly(N-vinylcarbazole) polymer matrix Fibrous and crystal structures of a helical polymer, poly-L-lactic acid (PLLA), were analyzed by using x-ray diffraction experiments. It was confirmed that the molecular residues were arranged on a nonintegral 10/3 helix as De Santis and Kovacs [Biopolymers 6,299 (1968)] reported. The atomic positions in a monomeric unit, which were proposed by Hoogsteen, Postema, Pennings, ten Brinke, and Zugenmaier [Macromolecules 23, 634 (1990)], were validated. However, the previous reports on the positions of the two helical chains were found to be in error. The correct positions were determined. The second helical chain shifts from the base center by 0.45, 0.25, and 0.61 A along a, b, and c axes. Besides, the second chain rotates by 2.46" with respect to the first. Distribution function of the crystallites in various drawn fibers were determined as a function of spiral angle. Optical gyrations of PLLA and poly-D-lactic acid fibers were successfully measured by using high accuracy universal polarimeter, as functions of temperature and drawing ratio. By using x-ray data of the change of the fibrous structure by drawing treatments, the gyration tensor components of PLLA could be calculated. It is of great interest that gyration tensor component g3a along the helical axis is extremely large, -(3.85+O.69)X1O-2, which corresponds to a rotatory power of (9.22 1.7)X 103"/mm, about two orders of magnitude larger than those of ordinary crystals. This is the first experimental evidence that helical polymers will produce enormous optical activity in the solid state. Helical polymers will be important for the elucidation of gyro-optical properties of solids and promising for new optical applications utilizing their large optical activity. 0 1995 American Institute of Physics.

The direct and converse piezoelectric effects have been observed in the Achilles tendon of ox and horse, which consists of collagen fibers in which the collagen molecules are highly orientated and crystallized. The matrix of piezoelectric constant is concordant with that derived for and unidirectionally oriented system of crystallites of collagen with a hexagonal symmetry. The magnitude of piezoelectric constant is: -d 14=d 25=8.0×10-8, d 15=d 24=4.2×10-8, d 31=d 32=0.26×10-8, d 33=0.2×10-8 c.g.s.e.s.u. respectively, which are the largest values observed in the crystalline polymers. The origin of the effect is supposed due to the polarization or displacement of hydrogen bonds being formed in the polypeptide chains of collagen crystals. The gramophone pick-up can be made by using the thin sheet of tendon as an electromechanical transducer.

Piezoelectric properties have been studied for the composite systems of PZT ceramics and polymers including polyvinylidene fluoride (PVDF), polyethylene (PE), and polyvinyl alcohol (PVA). The values of the piezoelectric constants and their temperature and frequency dependences were discussed on the basis of the theoretical expressions of the piezoelectric constants for a two-phase system with piezoelectric spherical dispersions. The piezoelectric activity of all the composite systems studied was mainly ascribed to the piezoelectricity of PZT ceramics. For the PVDF-PZT system, the piezoelectricity of PVDF was shown to make minor contribution compared to that of PZT ceramics. For the PE-PZT system, the temperature dependence of the d constant due only to elastic relaxation in the PE phase was investigated. For the PVA-PZT system, the retardational and relaxational frequency dependence of the d constant observed above 80 °C were successfully accounted for in terms of the interfacial and electrode polarizations due to the dc conduction in the PVA phase.

No abstract

The complex dielectric, elastic and piezoelectric constants were measured for the composites of epoxy resin and ferroelectric PZT ceramics at 10 Hz as a function of temperature, and the magnitudes and loss tangents of these constants were compared with the theoretical predictions. The piezoelectric constants for a two phase system with piezoelectric spherical inclusions were expressed in terms of the properties of the constituents by use of the known expressions of the dielectric and elastic constants. The observed values of the d-constant (electric displacement/stress) were about 3/4 of the predicted. In the local mode dispersion region of epoxy resin near -30°C, the g-constant (electric field/stress) showed a larger temperature variation than the theoretical prediction.

No abstract