CAREER: Transport Phenomena and the Uptake of Foreign Species during Crystal Growth

Non-Technical Summary:

Industrial crystallization is a widespread process that plays a critical role in the manufacture of bulk and fine chemicals, food products, pharmaceuticals, and a very large number of materials. Crystallization processes often occur from complex mixtures that contain the desired product that is being crystallized, together with several other chemicals (e.g. additives, or by-products from manufacturing).

In this context, controlling the extent to which these impurities incorporate in the crystalline material is critical to control its final properties (in materials design) and to mitigate potential adverse health effects (for pharmaceutical products). This CAREER award, funded by the Solid State and Materials Chemistry program in NSF’s Division of Materials Research, investigates how these foreign species interact with the crystallizing product, with particular focus on their behavior as they approach the crystal surface.

The project involves several studies set to investigate the attraction of foreign species to specific faces of the crystal, imaging the structure of the liquid that surrounds the growing crystal, and studying the degree of incorporation control that can be achieved by modifying the structure of that surrounding liquid. This research is integrated with an education and outreach plan, involving chocolate crystallization workshops for hundreds of middle and high school students, and research opportunities with industrial mentorship for dozens of undergraduate students and a graduate student.

Beyond the training of those students in a field that is in high demand, results from the research will set the grounds for the development of new crystalline materials that use dopants to fine-tune their properties in continuum, and for the effective rejection of potentially toxic impurities from pharmaceutical and food products.

Technical Summary:

This CAREER award, funded by the Solid State and Materials Chemistry program in NSF’s Division of Materials Research, brings a new approach to the study of guest incorporation (impurities or dopants) during the growth of organic molecular crystals, with specific focus on the role of mesoscale kinetics on the formation of solid solutions. Despite the widespread use of inorganic solid solutions to control material properties throughout history (for example, in metal alloys), and the fact that non-stoichiometric lattice incorporation is one of the primary mechanisms by which potentially toxic process impurities are retained in pharmaceuticals, organic solid solutions are rarely studied in the academic literature.

These systems offer potential for tuning crystal properties in continuum, owing to the non-stoichiometric incorporation of the guest in a host’s crystal lattice. This project combines transport theory with laser interferometry to determine what drives the loss of face selectivity in crystals with anisotropic guest incorporation, to image and study the guest’s diffusion boundary layer during crystal growth from concentrated solutions, and to explain kinetic deviations from thermodynamic equilibrium in the formation of molecular solid solutions.

These goals are integrated with an education and outreach plan that connects students at very different levels to relevant topics in crystal engineering, while providing them with direct mentorship from industrial collaborators.

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.