Effects of flexoelectric and piezoelectric properties on the impact-driven ignition sensitivity of P(VDF-TrFE)/nAl films

Abstract

Polyvinylidene fluoride (PVDF) and its copolymer poly(vinylidene fluoride-co-trifluoroethylene), P(VDF-TrFE), have attracted great interest due to their ability to be utilized as a matrix binder capable of producing modified ignition sensitivity in energetic systems. While there have been studies on the combustion of fluoropolymer/aluminum systems, there is still a shortage of knowledge on the role the electromechanical properties of P(VDF-TrFE) play in the processes leading to the ignition of an energetic material upon a mechanical impact. To help bridge this gap, we conducted experiment and computational simulation to elucidate the underlying flexoelectric and piezoelectric properties that P(VDF-TrFE)/nanoaluminum (nAl) films exhibit and to quantify the time duration it takes to commence ignition (i.e., ignition time). Further, multiple samples of the P(VDF-TrFE)/nAl films were used in the experiment (20 specimens per run) and the simulation (5 microstructures) with similar statistical attributes for the microstructure, allowing us to perform a probabilistic analysis on the film's ignition sensitivity. Based on our systematic assessment, we conclude that the electromechanical properties of the film, especially flexoelectricity, can influence the ignition sensitivity by locally enhancing the electric field near the nAl particles (by a factor of ∼6.0) beyond the binder's breakdown strength, resulting in concentrated channels of heat dissipation and ultimately ignition reactions. The effect of poling was also investigated by comparing how the sensitivity of the poled films differs from that of the unpoled films, thereby offering a mechanism to tune the ignition sensitivity by varying the level of piezoelectricity in the films. Results indicate that poling the films can enhance the ignition sensitivity slightly by decreasing the minimum ignition energy (MIE) by 8%.