Mechanical shock-induced nucleation in solution: Is cavitation necessary?

Abstract

Mechanical shock-induced nucleation (MSIN) of crystals from aqueous supersaturated solutions of ammonium chloride is reported. A simple apparatus was constructed to expose solutions in glass vials to a single impact, while images were recorded using a fast camera. A strong correlation between cavitation in the liquid and nucleation of solid ammonium chloride was revealed. The measured fraction of solutions nucleated as a function of impact height was fitted using a Poisson model. The mean number of solution samples nucleated increased quadratically with impact height above a threshold height. Analysis of images showed that the accelerations achieved were sufficient to induce cavitation based on the cavitation number proposed by Pan et al. [Proc. Natl. Acad. Sci. USA 114 (2017) 8470]. The use of a hydrophobic coating on the internal glass surface was shown to significantly increase both the number of cavities observed and the probability of MSIN of solid crystals. The results presented suggest that MSIN of ammonium chloride salt is mediated by cavitation.