Recent developments of polar piezoelectric polymers

Following the extensive studies on the piezoelectric, pyroelectric and ferroelectric properties of polyvinylidene fluoride and its copolymers, a vast number of polymers were investigated for these properties. Piezoelectric thin films of polyurea were prepared by vapor deposition polymerization in vacuum and stable up to 200 degrees C. Piezoelectric odd nylon was characterized by the field induced rotation of amide dipoles in the molecular sheet crystalline structure. Completely amorphous vinylidene cyanide copolymers produced a remanent polarization proportional to the large dielectric relaxation strength during poling. Drawn films of polylactic acid exhibited the large shear piezoelectricity due to the crystalline structure of helical molecules, however, a remnant polarization was also produced by poling at high temperatures. Various polymers containing dipolar groups of carbonyl, urethane, urea and thiourea bonds were poled and their ferroelectric hysteresis was observed. Application of magnetic field as high as 10 Tesla to the liquid crystalline state of helical molecules of poly-gamma-benzyl-L-glutamate during film formation resulted in a very high shear piezoelectric constant 26 pC/N. Unprecedented high piezoelectric constant such as 1000 pC/N. was found in the highly hydrated cornea membrane consisting of collagen fibrils.