(296e) Computational and Experimental Investigations of Laser-Induced Nucleation

Recent experiments have demonstrated that intense, nanosecond laser pulses can induce crystal nucleation from supersaturated solutions that are transparent at the incident wavelengths, a phenomenon termed nonphotochemical laser-induced nucleation (NPLIN). Previous work has proposed that this effect is due to the alignment of solute molecules in solution due to the electric field of the applied laser light, promoting crystalline order. However, we show that lasers can also induce bubble nucleation of a volatile dissolved solute. We demonstrate bubble nucleation in supersaturated aqueous carbon dioxide solutions exposed to 9 nanosecond pulses of 355 nm, 532 nm, and 1064 nm laser light. We also show that as the supersaturation (the driving force for nucleation) is increased, less energy is required from the laser in order to induce bubble nucleation. This laser-induced bubble nucleation has implications for previously-proposed mechanisms of laser-induced nucleation, and may suggest new possibilities for this mechanism. We also present here the first molecular simulation of NPLIN examining how an orientational bias in solution affects nucleation with Monte Carlo simulations of a Potts lattice gas model. We examine this effect within both a classical, one-step nucleation framework as well as in the context of two-step nucleation. Our results indicate that an orientational bias can reduce the free energy barrier to nucleation within the one-step mechanism and promote the crystallization of precritical nuclei (the rate-determining step in the two-step mechanism). However, these effects for both mechanisms are only present with field strengths that are much greater than those reported in experiments.