On the Mechanism and Utility of Laser-Induced Nucleation using Microfluidics

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Why does shining a laser on some liquid solutions cause them to crystallize? The reasons for this phenomenon remain a mystery. Elucidating the mechanisms by which light can induce nucleation, the process by which molecules cluster together and organize during the earliest stages of crystallization, is the aim of this proposal. Understanding these mechanisms could result in “greener” industrial processes by which a wide range of materials and chemicals that we use every day, such as dyes and pharmaceuticals, are made, saving energy and reducing the need for large amounts of chemical solvents. In addition to reducing the environmental impact of manufacturing crystalline materials, laser-induced nucleation has the potential to provide better control over crystal shape and the arrangement of molecules in the crystals during the manufacturing process, properties that can be optimized for a specific application of the material. To make greener crystallization part of undergraduate and graduate education, the project would create educational activities that train students from diverse backgrounds to engineer solutions based on this new approach to crystallization, making it an inherent part of basic chemical engineering education.This research program will design and study microfluidic nonphotochemical, laser-induced nucleation (NPLIN) of preselected organic molecules. Molecules that crystallize into different morphologies, into different polymorphs, and that follow single-step versus two-step nucleation will each be examined to understand their light-field induced nucleation mechanisms. The three different mechanisms that will be investigated in this work are i) the optical Kerr effect by which light can align molecules in a disordered solute cluster and thereby induce nucleation, ii) dielectric polarization in which light lowers the energy of slightly sub-critical solute clusters, and iii) the absorption of light by colloidal impurity particles resulting in the formation of nanobubbles that induce nucleation. Doing so will require the design of high-pressure microfluidics coupled with a pulsed, collimated laser beam, and investigations of laser-induced crystallization of ibuprofen, carbamazepine, and glycine crystals. The use of microfluidics will contribute a quantitative experimental methodology for NPLIN that can also distinguish single-step nucleation from two-step nucleation. The research discoveries will set the foundation for translating fundamental findings to practical applications.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.