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

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This grant will be used to develop non-photochemical laser-induced nucleation as amethod for providing nucleation-on-demand, for controlling crystal structure, and forimproving the current understanding of nucleation from solution. The basis of thistechnique is the discovery, made by the PIs several years ago, that intense near-infraredlaser pulses could induce crystallization in aged supersaturated solutions of small organicmolecules. In cases studied so far, laser-induced nucleation enhances the rate ofnucleation 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 thephenomenon. This "polarization switching" of polymorphs represents a clean method forcontrolling crystal structure. It is hypothesized that the oscillating electric field of thelight is aligning solute molecules in a pre-nucleating cluster, aiding its organization into aparticular crystal structure. The method also has the potential of creating newpolymorphs of some substances. New polymorphs constitute novel materials that mayhave important industrial applications.Over the next three years the PIs propose to gain a better understanding of the mechanismof non-photochemical laser-induced nucleation, by systematically studying itsdependence on illumination parameters such as intensity, wavelength, laser pulse widthand polarization state. With the same goal, they will also explore the effect of a strongstatic electric field on supersaturated solutions. Other experiments would focus onscreening a large number of solvent/solute systems, as well as melts, to correlate the formof the inducing electric field to the crystal structure that is induced. Such screeningwould also include a search for new polymorphs.