Hierarchical dl-Glutamic Acid Microspheres from Polymer-Induced Liquid Precursors

Nanostructured organic crystals have a broad application potential as pharmaceuticals, pigments, or catalysts. The development of facile and reproducible synthetic routes and the upscaling of the process, however, still remain a challenge. Here, we describe the synthesis of macroporous hierarchically structured microspheres with nanoplatelets as building blocks of a model organic molecule—dl-glutamic acid (dl-Glu)—via a polymer-induced liquid precursor (PILP) phase using oppositely charged polyethylene imine (PEI) as a polymeric additive. The impacts of experimental parameters such as [dl-Glu], temperature, solvent composition, and the pH value were systematically investigated for the dl-Glu morphosynthesis process. A mechanism is suggested to explain the precipitation of dl-Glu with PEI as an additive based on a multistep process: (1) the formation, growth, and coalescence of the PILP droplets; (2) the homogeneous nucleation of nanoplatelets within PILP droplets and (3) the reorientation of nanoplatelets...