Modeling of the viscoelastic properties of PVDF through the fractional differential model

Polyvinylidene fluoride (PVDF), a piezoelectric material has many useful applications like sensors, transducers and surface acoustic wave devices. Since PVDF is a polymer, it is possible that its mechanical response is likely to be frequency and time dependent. It is important therefore, to characterize the frequency or time dependent behavior of PVDF using appropriate models that are based on experimental observations. Dynamical Mechanical Tests were conducted on bi-axially stretched PVDF at different temperatures (35°C-70°C) and frequencies (0.33Hz-10Hz). It was observed from the experimental results that at higher temperatures, the rate of change of modulus with frequency reduces. Time-temperature superposition was done for the storage and the loss modulii to arrive at a single master curve at a temperature of 35°C. The results obtained by the superposition were then modeled using a simple viscoelastic three parameter model with ordinary dashpot. This model predicted the storage modulus well but was found short of the required predictive capability for the loss modulus. A four parameter model with fractional dashpot was used and it is found that it models the loss and storage modulus results better than the model with ordinary dashpot. © 2008 COMADEM International.