Non‐photochemical laser‐induced nucleation (NPLIN) has been a growing field of study since 1996, and more than 40 compounds including organics, inorganics and proteins have now been probed under various conditions (solvents, laser types, laser beams etc.). The potential advantages of using this technique are significant, in particular polymorphic control. To realize these benefits, the objective is a carefully designed experimental setup and highly controlled parameters, for example temperature and energy density, in order to reduce the uncertainty regarding the origin of nucleation. In this paper, a new experimental setup designed to study NPLIN is reported. After a full technical description of the present setup, the different functionalities of this device will be illustrated through results on glycine. Glycine crystals obtained through NPLIN nucleate at the meniscus and exhibit different morphologies. The nucleation efficiency, as a function of the supersaturation of the solution used and the laser beam energy density, has also been established for a large number of samples, with all other parameters held constant.
A detailed understanding of liquid propellant combustion is necessary for the development of improved and more reliable propulsion systems. This article describes experimental investigations aimed at providing such a fundamental basis for design and engineering of combustion components. It reports recent applications of imaging techniques to cryogenic combustion at high pressure. The flame structure is investigated in the transcritical range where the pressure exceeds the critical pressure of oxygen ðp > p c ðO 2 ¼ 5:04 MPaÞÞ but the temperature of the injected liquid oxygen is below its critical value ðT O2 < T c ðO 2 Þ ¼ 154 KÞ. Data obtained from imaging of OH Ã radicals emission, CH Ã radicals emission in the case of LOx=GCH 4 flames and backlighting provide a detailed view of the flame structure for a set of injection conditions. The data may be used to guide numerical modelling of transcritical flames and the theoretical and numerical analysis of the stabilization process. Calculations of the flame edge are used to illustrate this aspect. Results obtained may also be employed to devise engineering modelling tools and We wish to thank CNES, Snecma and CNRS for their continuous support of our work in rocket propulsion. The assistance of the ''Mascotte'' team of Onera under the leadership of Lucien Vingert and Mohamed Habiballah is gratefully acknowledged.
International audienceThis paper reports for the first time the crystallization of the carbamazepine (CBZ) molecule in two solvents (methanol and acetonitrile) using the non-photochemical laser-induced nucleation (NPLIN) technique. The metastable zone of CBZ is first determined experimentally for different temperatures in both solvents. Then, the prepared solutions are irradiated by a 532 nm wavelength nanosecond pulsed laser and permitted to obtain CBZ crystals of phases I and III. The impact of laser power and polarization (circularly (CP) and linearly (LP)) on the CBZ crystallization efficiency in both solvents is determined through experiments. According to the results, the crystallization efficiency is significantly higher in methanol than in acetonitrile, and it is higher in solutions irradiated by CP laser than those by LP laser. Moreover, the irradiation of an acetonitrile solution by a LP laser results in CBZ phases I and III, whereas irradiation by the CP laser leads to CBZ phase III crystals. An ab initio determination of the interaction energy of different pairs of CBZ has been carried-out that enables the explanation of the nucleation in acetonitrile for both polarizations. In methanol, only CBZ phase III is obtained, which is in agreement with the ability of methanol to create noncovalent interactions preventing the CBZ phase I and II nucleation
Non-photochemical laser-induced nucleation (NPLIN) is an original and promising nucleation method that has been applied with success to small-molecule organic compounds, proteins, and inorganic compounds, leading to almost 50 publications. After the first application of NPLIN to glycine and carbamazepine, our team has performed NPLIN experiments on sulfathiazole (STZ) for the following reasons: (i) STZ is considered as a model drug for studying polymorphism; (ii) some STZ polymorphs present a two-dimensional packing type, while others have one-dimensional packing; (iii) STZ solubility curves, crystal habits, and crystallization characterization are well documented. First, we have determined the metastable zone limit of STZ in water/ethanol (v/v 1:1) for three temperatures (15, 25, and 40 °C). STZ metastable solutions have been irradiated with a nonfocused nanosecond laser (532 nm) at 25 °C. Nucleation induction time and crystal habits have been compared with those obtained by spontaneous nucleation. Nucleation site is the air/solution interface. We have noted Ind 50 (β) the laser intensity required to induce nucleation with 50% efficiency for a given supersaturation coefficient β. The use of this index has allowed us to compare NPLIN experiments for different compounds in different solutions. A dependency of STZ crystal size and crystal number on the irradiation duration, i.e., pulse number, has been established. Moreover, the obtained crystals have been characterized by Raman spectroscopy and X-ray single crystal diffraction. The role of laser polarization (linear or circular) has been established in comparison with spontaneous nucleation. In order to gain a deeper understanding of this behavior, we have calculated ab initio interaction energies for all dimers existing in the different STZ polymorphs. Theoretical results are coherent with observations.
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