Chemical Engineering and product and process design are continually evolving as both our fundamental understanding of molecular interactions increases and as the areas of interest for cutting edge research have evolved from liquids to micro-structured products such as pharmaceuticals, food products, solar cells and nanowires. Our goal is to use this continually increasing knowledge of molecular interactions to develop experimentally verified predictive models that can be implemented on time scales relevant for product and process development of new materials. The focus of my research has been in the area of the crystallization of organic molecular systems such as those found in the pharmaceutical and food products industries. Two of the primary product properties desired for crystallization are the polymorph (packing structure) and habit (shape), since the physical, chemical and processing properties of the crystal are highly dependent on both of those product properties.

One of my research thrusts has been to develop methodologies to predict the growth and dissolution rates of faceted crystal surfaces. These growth and dissolution rates are the foundation for the prediction of dynamic shape evolution and solution mediated polymorphic phase transformations. The growth and dissolution model is based upon the spiral mechanism of Burton, Cabrerra and Frank¹, and it takes into account the effect of important process parameters such as solvent, temperature and supersaturation. The model has been automated by eliminating the need for arbitrary human decisions², and generalized to account for organic molecules of API-level complexity³. The predictions of this model have been validated by comparison to experimentally observed crystal shapes obtained in our laboratory and from the literature.

These methods for the prediction of growth and dissolution rates can be used to predict morphology changes given a faceted shape evolution model. Thus, I have developed such a faceted shape evolution model in the context of both growth and dissolution⁴. The relative growth and dissolution rates needed to implement this model can come from the a priori methods described above, or from previously measured experimental data. The model demonstrates that a crystal's shape evolves toward the single stable steady state shape in growth; however, it evolves away from the single unstable steady shape in dissolution. In addition, the predictions made using the methods above and the dissolution shape evolution model have been validated using video microscopy in a Peltier viewcell⁵. The growth and dissolution models also have been combined to demonstrate the feasiblity for the use of cycles of growth and dissolution for the enhancement of crystal shape⁶.

Additionally, I have a strong interest in teaching all aspects of the chemical engineering curriculum. In addition to crystallization, one particular area in which I have developed a unique expertise throughout my graduate career is that of conceptual design using the hierarchical decision procedure of Douglas⁷. The systematic nature of this decision making process allows for the rapid selection of a near-optimal design, and similarly to my research in crystallization the decisions are highly dependent on the underlying fundamental physics and chemistry. This combined experience in teaching process design and research in product and process design for crystallization provides a synergistic path forward for the development of product and process design methodologies for crystallization as well as new research areas.

1. Burton, W.K., Cabrera, N., and Frank, F.C., “The Growth of Crystals and the Equilibrium Structure of their Surfaces,” Phil. Trans. R. Soc. 1951; 243, 299.

2. Snyder, R. C. and Doherty, M. F., “Predicting Crystal Growth by Spiral Motion”, in preparation.

3. Snyder, R. C., Sizemore, J. P. and Doherty, M. F., “Growth Prediction for Molecular Crystals of API-Complexity”, in preparation.

4. Snyder, R. C. and Doherty M. F., “Crystal shape evolution during dissolution and growth”, AICHE J. 2007; 53: 1337-1348.

5. Snyder, R. C., Veesler S. and Doherty M. F., “The Evolution of Crystal Shape During Dissolution: Predictions and Experiments”, in preparation.

6. Snyder, R. C., Studener S. and Doherty M. F., “Manipulation of Crystal Shape by Cycles of Growth and Dissolution”, AICHE J. 2007; 53: 1510-1517.

7. Douglas, J. M., “Conceptual Design of Chemical Processes.” Boston, MA., McGraw Hill Inc., 1988.