Non-Photochemical Laser-Induced Nucleation to Provide Crystallization-on-Demand and to Control Crystal Structure

Polytechnic University Of New York, Brooklyn NY

Investigators

Abstract

This grant will be used to develop non-photochemical laser-induced nucleation as a method for providing nucleation-on-demand, for controlling crystal structure, and for improving the current understanding of nucleation from solution. The basis of this technique is the discovery, made by the PIs several years ago, that intense near-infrared laser pulses could induce crystallization in aged supersaturated solutions of small organic molecules. In cases studied so far, laser-induced nucleation enhances the rate of nucleation by a factor of 10 13 . Even more intriguing is the case of aqueous glycine, which crystallizes into two different polymorphs depending on the laser polarization state (linear vs. circular), which implicates the optical electric field as being responsible for the phenomenon. This "polarization switching" of polymorphs represents a clean method for controlling crystal structure. It is hypothesized that the oscillating electric field of the light is aligning solute molecules in a pre-nucleating cluster, aiding its organization into a particular crystal structure. The method also has the potential of creating new polymorphs of some substances. New polymorphs constitute novel materials that may have important industrial applications. Over the next three years the PIs propose to gain a better understanding of the mechanism of non-photochemical laser-induced nucleation, by systematically studying its dependence on illumination parameters such as intensity, wavelength, laser pulse width and polarization state. With the same goal, they will also explore the effect of a strong static electric field on supersaturated solutions. Other experiments would focus on screening a large number of solvent/solute systems, as well as melts, to correlate the form of the inducing electric field to the crystal structure that is induced. Such screening would also include a search for new polymorphs.