Piezoelectric Characteristics of Poly($\gamma$-benzyl-l-glutamate) Film Oriented under Strong Magnetic Field

To attempt the realization of a highly piezoelectric polymer film, we used an oriented poly($\gamma$-benzyl-l-glutamate) (PBLG) film that was cast from chloroform solution under the strong magnetic field induced by a generation apparatus using a superconducting magnet. First, the orientation of the PBLG principal chain in the film was observed macroscopically by polarizing microscopy (POM), and it was found that the orientation of the principal chain differed in each region. Then, in order to observe each region, using our original apparatus, the birefringence (retardation) and optical axis were measured at 100 μm pitch/point-to-point, and a cm-order region with high retardation was found. We then cut off a small piece from this region of the PBLG film and evaluated the shear piezoelectric constant. A large shear piezoelectric constant of 18 pC/N was found in the small piece. Also, the PBLG film was investigated by atomic force microscopy (AFM). We found a characteristic slender structure in the region with a high macroscopic shear piezoelectric constant. Furthermore, the piezoelectric motion due to its shear piezoelectricity in the region was investigated microscopically by piezoresponse force microscopy (PFM), which successfully enabled the direct observation of the piezoelectric displacement due to its shear piezoelectricity in one direction in the entire region with the characteristic slender structure. On the basis of these results, we speculate that the principal chain was highly oriented and crystallized in the region with the characteristic slender structure, resulting in a large shear piezoelectric constant in the region.