Organic crystals are principal building blocks for food, pharmaceuticals, and consumer goods. Crucial performance characteristics such as stability of formulations, the color of pigments, <i>etc</i>. are decided by the choice of shape and size of the crystals. The desired morphology of the crystal can be achieved by tailoring the process parameters like cooling rate, shear rate, or use of additives.  In this study, we tune the crystal shape and size of stearic acid crystals during crystallization. Highly deformed crystal structures can be obtained in the presence of additive during crystallization. The range of crystal shapes spans rhombic to fractal-like and spherulitic structures. For an increasing concentration of additive, the crystal morphologies observed in a sequence are: perfectly rhombic, deformed rhombic shape with needles at the edges, tree-like structure, densely branched tree-like structure and spherulitic structure. In addition, the higher the relative supersaturations of stearic acid, the higher the concentration of additive required for the shape transitions. This evolution of different crystal habits can be related to the facial growth rates of the crystals. The growth rates are dependent on the molecular interactions of solute and additive at the growing edge. Any instability and/or change in adsorption energies of solute (stearic acid) and additive at the growing interface affect the growth rate and eventually affect the crystal habit. In this talk, we present a framework to understand this change in morphology based on the mechanism of crystal growth due to the adsorption of additive on the growing interface of crystal.

Engineering crystal morphology using an additive: Case study of stearic acid

Macromolecular Chemistry: The Second Century

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ACS Spring 2020 National Meeting & Expo

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.