Altering surface chemistry and mechanical properties of aluminum nanoparticles to enhance reactivity

This research focuses on methods of harnessing the stored chemical energy within an Al particle based on altering the surface chemistry, mechanical, and structural properties of the particle by functionalization or stress-altering (pre-stressing (PS) and super-quenching (SQ)). Functionalizing nAl particles by coating the particles surfaces with molecularly bonded species alters the surface chemistry of the particles. And pre-stressing the particles by annealing and quenching (slow quenching: PS and fast quenching: SQ) alters dilatational strain and stress and is correlated with increased particle reactivity in different media. Nano-Al particles with and without surface functionalized self-assembled monolayer (SAM) of perfluorohexadecanoic acid (PFHD) are combined with kerosene and the resulting nanofluids are examined for changes in droplet regression/combustion and evaporation behavior associated with manipulating particle surface chemistry. Similarly, nAl particles are pre-stressed by annealing to 573K, then quenched at two different cooling rates (PS and SQ), to induce elevated dilatational strain and/or stress within the nAl particles, mixed with a solvent-binder system comprised of acetone and dimethylformamide (DMF) co-solvent and Poly (vinylidene fluoride) (PVDF) to synthesize energetic thin films. The processing, morphology, and characterization of these energetic films are examined under low velocity drop-weight impact, thermal ignition burn rates, rheology regimes, and Transmission (Scanning) Electron Microscopy (TEM and SEM). Results are rationalized with the help of simple stress-strain mechanical and Density Functional Theory (DFT) models that consider creep in the alumina shell, elastic stresses, and delamination at the core-shell boundary. The models predict different shell failure mechanisms at different quenching rates. These studies introduce promising techniques to alter particle surface chemistry and mechanical properties.