Abstract

We report our recent results on the effect of impurities or ‘imposter molecules’ on the crystal growth process and developing mechanistic models describing the mechanisms by which impurities influence crystal growth. Impurities affect growth kinetics at the scale of kink attachment and detachment events, which are too fine to examine experimentally in real time. Thus, simulations are used to study the proposed mechanisms for growth inhibition/promotion and the results will be compared to experimental data available in the current literature.  As a starting point,  Kinetic Monte Carlo (KMC) simulations are utilized to simulate  the time evolution of centrosymmetric organic crystal growth. Rare event rates are determined as functions of energetic barriers for desolvation and attachment/detachment works. Various mechanisms have been proposed to explain the growth-inhibiting effect of impurities, including step-pinning and spiral-pinning, which are described herein. These mechanisms will be incorporated into the KMC simulations, and compared to experimental values for validation. Once we have established effective working models, we will look to publish our results and ideally incorporate them into ADDICT3 (Advanced Design and Development of Industrial Crystallization Technology - version 3), an engineering tool which predicts relative growth rates and crystal morphology of solution-grown faceted crystals [1].

Additionally, we report on some new developments in ADDICT3 to improve the workflow during concep- tual design of crystalline solid processes. ADDICT3 is capable of predicting the shape and morphology of crystalline particles using only the following input data, (1) crystal structure, (2) atom-atom force field, and (3) specified solvent and growth conditions. The key outputs are the steady-state growth shape and morphology of the crystals, and the “shape triangle” which gives graphical information about the influence of design variables (temperature, supersaturation, solvent) on the resulting shape and morphology of the crystal. More detailed outputs are also provided (e.g., periodic bond chain networks, growth spiral shapes, etc.) for use by the more sophisticated user. The tool can be used alone or in combination with other tools that have been developed recently to aid in the design of crystallization processes.