Poly(gamma-benzyl alpha, L glutamic acid)-based piezoelectric films & microfibers.

摘要

Piezoelectric materials in use today are often made of ceramic crystals. Although most ceramics offer high piezoelectricity, they are brittle and require expensive processing conditions. For applications where flexibility is required in addition to high piezoelectric activity, polymers are a very attractive alternative.;An ideal piezoelectric material is the one where the piezoelectricity and mechanical properties can be altered individually so that the mechanical stiffness of the material can be varied for particular applications or tuned to match that of the surroundings (e.g. air or water) for increased transduction sensitivity. This is typically achieved by production of composite materials containing piezoelectric and matrix components. Here, we present new composite films and microfibers based on the biopolymer, poly(gamma-benzyl alpha,L-glutamate) (PBLG) and discuss their fabrication and piezoelectric properties.;Fabrication of PBLG films and fibers was made possible by PBLG's extreme solubility in organic solvents. By simultaneous poling and curing of PBLG/methylmethacrylate (MMA) mixture solutions via corona charging, we fabricated a flexible composite film [80% PBLG and 20% Poly(methylmethacrylate) (PMMA)] with approximately 20% of the PBLG molecules oriented normal to the film surface. This PBLG film exhibited high piezoelectricity (d33 = 20 pC/N), and its Young's modulus was 1 GPa. However, significant amount of MMA evaporated during the corona charging process that precluded the fabrication of films with pre-determined PBLG-PMMA composition. We also fabricated thick composite disk (thickness: 3 cm) by breakdown charging and thermal polymerization of PBLG/PMMA mixture solution, a process that does not allow MMA evaporation. The composite disk exhibited low piezoelectricity (d33 ∼ 3 pC/N) due to low PBLG content ( 30%); however, its mechanical characteristics were similar to those of PMMA, indicating that the piezoelectricity and mechanical strength are independently related to the two polymer components of the composite disk. By electrospinning PBLG/dichloromethane (DCM) solutions under potentials of -(12∼15) kV, we produced piezoelectric microfibers (diameter: 100 nm) with nearly all of the PBLG dipoles oriented along the fiber axis, evidenced by x-ray diffraction. The PBLG fibers showed high piezoelectricity (d 33 = 32 pC/N), and an elastic modulus of 570 MPa.;Both the piezoelectric film and fiber systems can be fabricated directly from solution in a mould or on a substrate. Due to the versatility in the fabrication process and the high piezoelectricity, these materials show great promise as transducer materials for loud speakers, microphones, and/or energy harvesting devices.