On the mechanism and utility of laser-induced nucleation using microfluidics

This research will be led by Ryan Hartman, professor, with co-principal investigator Bruce Garetz, professor and Associate Chair, the Department of Chemical and Biomolecular Engineering at NYU Tandon.

Why does shining a laser on some liquid solutions cause them to crystallize? The researchers are awarded a National Science Foundation (Chemical, Bioengineering, Environmental, and Transport Systems) grant to elucidate the mechanisms by which light can induce nucleation — the process by which molecules cluster together and organize during the earliest stages of crystallization. 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 will 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.

Specifically, the research program will design and study microfluidic nonphotochemical, laser-induced nucleation (NPLIN) of preselected organic molecules. To understand light-field induced nucleation mechanisms, the investigators will examine molecules that crystallize into different morphologies, into different polymorphs, and that follow single-step versus two-step nucleation. The team will look at three different mechanisms: 

• The optical Kerr effect by which light can align molecules in a disordered solute cluster and thereby induce nucleation
• Dielectric polarization in which light lowers the energy of slightly sub-critical solute clusters
• The absorption of light by colloidal impurity particles resulting in the formation of nanobubbles that induce nucleation.

As part of the project, and in order to do many aspects of this research, the team will design high-pressure microfluidics coupled with a pulsed, collimated laser beam, and perform 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.