Bioelectrets and biopiezoelectricity

Some biopolymers possess polar uniaxial orientation of molecular dipoles and show pyroelectricity and piezoelectricity. Some examples of bioelectrets are described. Shear piezoelectricity is observed for elongated films of poly-L-lactic acid (PLLA). Temperature relaxations in the complex piezoelectric constants, the elastic constant, and the permittivity are observed at the glass transition temperature, approximately 90 degrees C. However, the piezoelectric constants for the crystalline phase of PLLA calculated from a spherical dispersion theory are independent of temperature. Thin layers of aromatic polyurea prepared by vacuum deposition polymerization show pyroelectricity and piezoelectricity after poling, which are stable to 200 degrees C.<>