Do we need perfect mixing between fuel and oxidizer to maximize the energy release rate of energetic nanocomposites?

Abstract

It is well accepted that close assembly between a fuel and an oxidizer can increase the interfacial contact-area and reduce the diffusion distances, which can significantly promote a heterogeneous reaction. However, we recently observed for nanocomposites of Al/PVDF (aluminum/polyvinylidene fluoride), that if we separated some of the PVDF to form a laminated structure, the flame propagation rate is significantly increased compared to the homogenous case. To probe the mechanism behind this, we used functionalized aluminum nanoparticles to create microsized aggregates of Al-rich and PVDF-rich regions to induce the inhomogeneity and also fabricated Al/PVDF laminate structure films to control the inhomogeneity systematically. The result demonstrates that the inhomogeneous mixing between Al and PVDF can significantly increase the flame front corrugation (burning area). This presumably occurs due to variations in the microburn rate (local burn velocity vectors at the flame front on the microscale). The benefit of the enhanced flame area can apparently overcome the effects of the decrease in the contact area, leading to enhanced burning for an inhomogeneously mixed system. Finally, fluorocarbon functionalization of Al particles can further increase the microburn rate.