Piezoelectric properties of polypeptide-PMMA molecular composites fabricated by contact charging

The most common piezoelectric materials (PM) in use today are ceramic crystals which are heavy and brittle despite high piezoelectricity. Polymer-based PM is an alternative to ceramic crystals but they have lower piezoelectric coupling constants which deteriorates quickly at high temperature. In an effort to develop non-brittle and light PM with stable piezoelectric properties, we explored fabrication of composite materials comprising piezoelectric α-helical poly(α-amino acids), poly(γ-benzyl α,l-glutamate) (PBLG) and matrix polymer, poly(methylmethacrylate) (PMMA). Thick composite disks were created by contact charging of PBLG–MMA solution mixture followed by curing the MMA matrix in a designed mold. Compared to our prior method of corona discharge, this new method allowed the application of predefined electrical fields to the PMMA solution with little MMA evaporation. This communication presents the fabrication and characterization of a series of PBLG–PMMA composite disks with various PBLG compositions prepared under different poling conditions. The results show for the first time that all PBLGs can be poled in the direction normal to the disk surface and that the poled PBLGs within the PMMA matrix are directly responsible for the piezoelectricity of the composite materials. The two-polymer composite system allows independent modulation of film’s mechanical properties and piezoelectricity at a molecular level.