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Manipulating Crystal Orientation in Nanopores

The UMN MRSEC has demonstrated the control of nanocrystal orientation within nanoporous polymer monoliths prepared from ABC triblock terpolymers containing a robust A block (polystyrene), a hydrophilic B block [poly(dimethylacrylamide)], and an etchable C block (polylactide) developed in the IRG. He has embedded glycine nanocrystals within the monoliths by evaporating the water from aqueous solutions imbibed by the pores. The glycine nanocrystals adopted the β polymorph, which is unstable on macroscropic length scales, and aligned with their fast growth needle axis parallel to the cylindrical pore walls. The β-glycine nanocrystals are polar and chiral, and certain chiral auxiliaries bond selectively to the crystal face perpendicular to the fast-growth direction, impeding its growth. The addition of these chiral auxiliaries to the aqueous solutions imbibed by the monoliths resulted in the β-glycine nanocrystals adopting different orientations within the pores consistent with a new fast-growth direction aligning parallel to the pore walls. A schematic of the results is depicted below. The ability to control nanocrystal orientation within porous matrices suggests new routes to producing nanocomposite materials. This work will be featured on the cover of an upcoming issue of the Journal of the American Chemical Society.