Abstract
The controlled preparation of different crystal morphologies with varying preferential orientation with respect to the substrate is of crucial importance in many fields of applications. In this work, the controlled preparation of different phenytoin morphologies and the dependency of the preferential orientation of those crystallites is related with the preparation method (solvent annealing vs drop casting), as well as the physical–chemical interaction with the solvents in use. While solvent annealing induces the formation of particular structures that are partially dewetted, the drop casting technique from various solvent results in the formation of needle-like and elongated structures, with each having a distinct morphology. The morphologies are explained via the Hansen solubility parameters and correlated with the solvent vapor pressures. X-ray diffraction experiments reveal preferential orientations with respect to the solid substrate and indicate the surface-mediated stabilization of an unknown polymorph of phenytoin with an elongated unit cell in the b-axis.
Highlights
Defined thin film preparation of organic molecules on solid surfaces is of great importance in a variety of fields, including pharmaceutics,[1,2] organic electronics,[3−5] and colloid science,[6−8] among many more
Vacuum deposition of phenytoin results in completely amorphous thin films and different crystal morphologies with varying preferential orientation with respect to the silica substrate can be induced via solvent vapor annealing
The relatively slow vapor annealing process results in a preferential crystal growth in the 010 direction on vapor annealing in most of the tested solvents, while water and THF vapor induce a preferential orientation in the 001 direction
Summary
Defined thin film preparation of organic molecules on solid surfaces is of great importance in a variety of fields, including pharmaceutics,[1,2] organic electronics,[3−5] and colloid science,[6−8] among many more. Small particles can be obtained from phenytoin sitting on a solid silica surface via a spin-casting process, which results in an increased solubility and dissolution rate, both being strongly enhanced compared to the bulk material.[1] Another example is the achievement of surface-mediated polymorphic structures by changing the preparation condition within alkyl-terminated terthiophene thin films.[9−11] Small crystals may be obtained via atomic force microscopy, which initiates crystallization during scanning.[12]. The deposition via physical vapor deposition or drop casting is hardly recognized even though such processes are fast and reproducible, allowing the preparation of defined API layers on solid surfaces
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