Calculations of the elastic compliance and piezoelectric constants of poly(vinylidene fluoride) and poly(vinylidene fluoride-trifluoroethylene) crystals

We present calculated compliance and piezoelectric constants for polyvinylidene fluoride (PVDF) and its copolymer with trifluoroethylene P(VDF/TrFE). The constants were derived by minimizing the energy of the unit cell under various states of stress, using a modified molecular mechanics force field. The model was first validated against experimental data and theoretical calculations for the properties of PVDF. The behavior of the compliance and piezoelectric constants of P(VDF/TrFE) are examined as a function of the molecular percentage of VDF. It was found that an optimum value for the dielectric constant d 33 of P(VDF-TrFE) exists between 55 and 65 mol % VDF.