Toward Rational Design of Tailor-made Additives Using Growth Site Statistics

Tailor-made additives are generally designed by optimizing the chemical compatibility between an adsorbing additive and a flat crystalline surface. Crystal growth, however, mainly takes place at step edges where growth units incorporate into the advancing step. In this paper, a new method is introduced that quantifies the importance of all possible growth site configurations from Monte Carlo crystal growth simulations, taking the crystalline surface, steps, and other configurations into account. This allows the identification of growth site configurations that are good candidates for a blocking strategy using tailor-made additives. Application to an anisotropic Kossel model shows that the importance of growth sites at step edges is equal to or higher than the importance of growth sites at a flat crystalline surface. As a “real-world” example, aspartame phase II-A, which has a needle-like morphology, is studied. When comparing the needle side faces with faces on top of the needle, it turns out that there are a minor number of growth site configurations that have different contributions to the growth process. When these configurations are excluded from the growth process, in a first attempt to simulate the effect of a habit modifier, the results show a large blocking effect for flat faces. Rough growing faces, on the other hand, do not seem to be affected by the exclusion of growth site configurations from the growth process.