Abstract
Crystallization has been observed in laser-induced cavities in saturated solutions, but the mechanisms behind nucleation of crystals are not entirely clear. A hypothesis is that high solution supersaturation during the bubble growth period triggers the nucleation. Because of small spatiotemporal scales of the cavitation event, the supersaturation is very difficult to measure experimentally. To test the nucleation hypothesis, we perform a two-dimensional axisymmetric direct numerical simulation of an experimentally observed laser-induced cavitation event with crystallization. We demonstrate a significant degree of supersaturation and argue that the nucleation hypothesis is indeed plausible. To analyze factors that lead to a high supersaturation, we develop a comprehensive one-dimensional model for spherical laser-induced cavities. We conduct an extensive investigation on how the solute solubility, solute diffusivity, laser pulse energy, and superheated liquid volume affect the supersaturation. We show that high supersaturation is possible under a range of relevant conditions but not readily obtained for all solutions and laser setups. Guidelines are provided to identify if a specific solution or laser setup may attain high supersaturation. The insights obtained and the numerical methods formulated in this work can be applied to assess and design new laser-induced cavitation setups that allow for precise control of the duration and degree of the supersaturation
Highlights
Crystallization is the formation of crystalline solids from a fluid phase, and the process is utilized as an essential separation and purification technique in, for example, the pharmaceutical and fine chemicals industry.[1]
In the non-photochemical laser-induced nucleation (NPLIN) method, the solvent evaporation may occur around laser-heated nanoparticles, and in the laser-induced cavitation method the solvent is evaporated at the vapor bubble interface
We recall that in this experiment crystallization is observed in connection to the thermocavitation event, and that the purpose of the simulation is to test the nucleation hypothesis related to the high solution supersaturation around the bubble during the bubble growth phase
Summary
Crystallization is the formation of crystalline solids from a fluid phase, and the process is utilized as an essential separation and purification technique in, for example, the pharmaceutical and fine chemicals industry.[1] During the process of crystallization, it is necessary to control nucleation of the new crystalline phase in order to produce crystals with the desired quality features, such as crystal size, morphology, or purity. To investigate the hypothesis that solvent evaporation is a prerequisite for the nucleation, we focus in this work on the laser-induced cavitation method where the vapor bubbles have been observed in experiments and the solvent evaporation is known to take place
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