Tuning Hydrate Properties

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Non-technical AbstractOrganic molecules can crystallize in a variety of forms, some of which include water (hydrates, H) and others that do not (anhydrates, A). H and A forms differ in their physical properties and their relative stabilities. Changes in external parameters such as temperature and relative humidity can induce H to A transformations. Dehydration may be unintentional or intentional, though the mechanism(s) of the reaction and the structure(s) of the final products are difficult to predict. In this project, supported by the Solid State and Materials Chemistry Program in the Division of Materials Research, a deeper understanding of H to A transformations is developed through a combination of data mining efforts and experimental studies. The experimental studies make use of a range of complementary techniques available on site and through collaborations with researchers at United States National Laboratories. Developing a better conceptual framework for understanding water uptake/loss from crystalline solids can significantly improve our ability to predict the properties of this broad class of materials and to employ solid state dehydration as a rational means to create new crystalline forms. The insight gained through these studies has direct implications for materials that touch all aspects of society including pharmaceuticals, foods, electronic and energetic materials. Additionally, this research provides strong interdisciplinary training opportunities for students at many education levels and allows graduate students to gain valuable experience at national laboratories. Technical AbstractHydrates are an important class of molecular crystals, yet our collective understanding and ability to predict dehydration mechanisms and reaction products is quite limited. With support from the Solid State and Materials Chemistry Program in the Division of Materials Research, this research establishes correlations between hydrate packing motifs and specific dehydration mechanisms and anhydrous product topologies. Data mining efforts are used to identify packing motifs which favor particular dehydration mechanisms and anhydrous products. Time resolved synchrotron PXRD (at the Advanced Photon Source) and quasi-elastic neutron scattering (at NIST) are employed to monitor structural changes throughout the dehydration reaction and the associated water dynamics. The predictive power of the correlations identified through these structure-mechanism studies are then rigorously tested through dehydration studies on new hydrate systems. Doping studies which aim to restrict the molecular motions within the hydrate also help to refine our mechanistic understanding of how dehydration reactions occur in crystalline materials. This research provides strong interdisciplinary training opportunities for students at many education levels and allows graduate students to gain valuable experience at national laboratories.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.