Toward the Rational Design of Crystalline Surfaces for Heteroepitaxy: Role of Molecular Functionality

Abstract

The rational design of crystalline surfaces for controlling nucleation and crystal growth via heteroepitaxial mechanisms is of great importance in the manufacture of advanced functional materials, such as pharmaceuticals and semiconductors. Despite numerous studies investigating the singular effect of crystalline lattice matching, molecular functionality, or topography on epitaxial ordering, no study has been carried out investigating these effects in competition with one another in order to establish which effect is the most significant in promoting nucleation. Herein, we report the key results and conclusions from studying the heterogeneous crystallization of the stable polymorph of acetaminophen (AAP) on crystalline substrates with differing lattice parameters and surface functionalities. Induction time measurements were used to rank the ability of the different substrates in promoting heterogeneous nucleation. The results showed that nucleation was preferred on substrates whose surface functionality matched with that of AAP even when other substrates exhibited a better lattice match with specific AAP crystal faces. Furthermore through the use of single crystal X-ray diffraction and molecular modeling, the epitaxial ordering of AAP on single crystals of α-lactose monohydrate (α-LMH) and d-mannitol has been investigated in order to gain mechanistic insight into the nucleation process.