Strain in ferroelectric polymers under low-frequency electric fields: Experiments and modeling

The study of the electric field-induced thickness strain of ferroelectric polymers is very interesting because of the high actuating capabilities and various applications of these materials, such as electroactive materials for artificial muscles or as the active materials of membranes, due to their flexibility. This article reports on the effect on the strain properties of uniaxially and biaxially stretched β-form polyvinylidene fluoride when applying a low quasi-static triangular electric field E (100 mHz, E < 16 MV/m). For an applied electrical field at this level, the strain was proportional to the square of the electric field. The strain depended mainly on the electrostriction effect, linked to the induced reversal polarization and to interlaminar charges. The dielectric constant of the biaxially stretched polyvinylidene fluoride at 100 mHz was higher than for its uniaxially stretched counterpart. As a consequence, the induced charges and microscopic polarization for the first film exceeded those of the second one, and the electroactive strain for the biaxially stretched sample was more significant than for the uniaxially stretched film. This article first offers a description of the strain phenomenon through the polyvinylidene fluoride material during electrical excitation, after which a new model is presented. This model was developed to evaluate the induced electric current and strain phenomenon. A good agreement between simulations and experimental results was obtained.