Mechanochemical Ionization – Differentiating Pressure-, Shear-, and Temperature-Induced Reactions in a Model Phosphate

Using density-functional theory based molecular dynamics simulations, we study stress and temperature-induced chemical reactions in bulk systems containing triphosphoric acid and zinc-phosphate molecules. The nature of the reactants depends sensitively on the imposed conditions, e.g., isotropic and even more so shear stress create ionic reactants. Instead, zwitterions and water molecules emerge from thermal cycles. Hydrostatic stresses required for reactions to occur lie well below those typical for tribological micro-contacts and are further reduced by shear. During the moment of impact, many protons are mobile, even if they bond to groups that formally remain inert in a compression/decompression cycle. Our findings are consistent with a variety of observations on the triboelectric charging of insulators but contradictory to the hot-spot model.