Influence of Laser Parameters and Experimental Conditions on Nonphotochemical Laser-Induced Nucleation of Glycine Polymorphs

Abstract

Nonphotochemical laser-induced nucleation (NPLIN) is a promising primary nucleation control method, yet its underlying mechanism remains elusive. To contribute to the discussion on whether the polarization of laser irradiation in NPLIN experiments influences the polymorphic outcome, we revisit NPLIN experiments with aqueous glycine solutions with supersaturations ranging between S = 1.5 and S = 1.7 irradiated by nanosecond pulses (∼7 ns) of near-infrared wavelength (1064 nm). Systematically altering laser light excitation properties, including the number of pulses and type of polarization, we quantified the nucleation kinetics and characterized the polymorphic form that crystallized upon laser irradiation. Due to the stochasticity of the nucleation process, a large number of samples (>100 per each experimental point) were studied under carefully controlled experimental conditions such as the ambient temperature, cooling rate, and aging period. We observed significant differences among laser-irradiated, spontaneously nucleated, and crash-cooled samples in terms of nucleation kinetics and polymorphic form. This result indicates that laser irradiation provides a different polymorph-forming pathway in comparison to crash-cooling and spontaneous nucleation. However, no clear dependence between the polymorphic form and the polarization of laser irradiation is observed. We discuss our results in the context of previous reports supported thorough quantification of sample heating in NPLIN experiments.

Potassium Sulfate: A New Candidate to Explore Non-Photochemical Laser-Induced Nucleation Mechanisms

“…There are, however, reported cases, such as Alexander and Camp [6], showing that the induction time is not correlated to polarization geometry. In the case of glycine, Garetz et al [2,16] have shown that, for a range of supersaturation, the geometry of polarization induces different polymorphs, which was considered in this study as an argument in favor of the OKE model (although this experiment could not be reproduced) [17,19]. K 2 SO 4 exhibits two polymorphs-the β form (Pnam (62)) [29], which is stable up to 583 • C but transforms into the α form at a higher temperature (P6 3 /mmc) [30].…”

“…This is in line with the observation of Hua et al [35], who found that the number of crystal nucleated is proportional to the laser intensity. Yet, it should be underlined that Irimia et al [19] showed that the nucleation probability of glycine aqueous solutions actually decreases when more than 600 pulses are used due to the overall temperature increase (and associated supersaturation decrease) of the solution. For our study, the temperature increase was calculated for our experimental conditions (1 pulse at 85.6 mJ, β = 1.25) using the same theoretical model developed and experimentally validated by Irimia et al The calculated Cp value of 3.75 J g −1 K −1 led to an overall increase in temperature (in the area illuminated by the laser) of 2.4 × 10 −3 K/pulse, which was not sufficient to change the overall supersaturation of the solutions.…”

“…Several NPLIN cases have been claimed to rely on the OKE ever since [3,[14][15][16], but several researchers have questioned the systematic implication of this phenomenon. First, it appears that the polarization dependence of glycine polymorphism during NPLIN could not be reproduced [17][18][19]. Liu et al [20] measured the relative angle between urea crystals and the electromagnetic field and showed that there is no alignment of the crystal with the direction of polarization of the laser, contrary to Garetz's first observations [1].…”

Laser-induced nucleation promotes crystal growth of anhydrous sodium bromide

“…Polarization switching for glycine occurs only within a narrow window of supersaturation and temperature, and it has been found that switching is difficult to reproduce. 27,30,33,38,39 Polarization effects have also been observed in NPLIN of ʟ-histidine, 26 carbamazepine 28 and sulfathiazole. 29 The mechanisms of NPLIN are not fully understood.…”

“…[10][11][12][13][14][15] Non-photochemical laser-induced nucleation (NPLIN) is a technique in which a new phase is formed by the exposure of a metastable system to pulses of laser light. The phenomenon was first observed in supersaturated solutions of urea, 16 and has since been observed in a diverse range of systems including solutions of simple salts; [17][18][19][20][21][22] proteins; 23,24 small molecules in various solvents; 13,[25][26][27][28][29][30][31][32][33] and one-component systems. 34,35 NPLIN typically utilises millijoule, unfocused, nanosecond laser pulses in the visible or near-IR region of the electromagnetic spectrum at a wavelength that is not absorbed by the sample.…”