(702b) Impact of Droplet Evaporation on Polymorphism of Suberic Acid Crystallization

Polymorphism of organic molecular systems continues to be an important topic in crystallization, ranging from interests in structure screening, food products performance, and patent protection. While new potential pharmaceutical compounds regularly generate challenges in polymorphism, the identification of new polymorphs of more commonly studied compounds also continues. Suberic Acid is the eight carbon straight chain dicarboxylic acid, and it is used as a food additive, as a pharmaceutical precursor, and as an API conformer. Suberic Acid was thought to form only a single α polymorph until a second β polymorph was identified through DSC analysis and subsequent crystallization in nanoscale chambers (Ha et. al.). Among many techniques available to form crystalline particles is droplet evaporation, which can be done using a spray dryer at elevated temperatures, or using a vibrating orifice aerosol generator (VOAG), a Collison type aerosol generator, and a syringe pump constant flow aerosol generator.

In this talk, we highlight our work on forming crystalline suberic acid particles from a Collison type. While the α polymorph is formed using several solvents including water and ethanol, particle formation at low concentrations from isopropanol demonstrates the formation of a newly proposed γ polymorph of suberic acid. The formation of the unique structure is differentially identified from the α and β using powder X-ray diffraction (pXRD). Thermogravimetric analysis is further used to demonstrate that the new form is not a solvate. Differential Scanning Calorimetry together with variable temperature pXRD are used to demonstrate that the new polymorph is energetically similar to the α polymorph; however, it transforms to the α polymorph over time at temperatures below the known α/β transition point. The size distributions and impact of solution concentrations are also identified. Finally, we will discuss the broader opportunities/challenges/insights potentially available from using these droplet evaporation methods more commonly used to study atmospheric aerosols in a crystallization context.

Ha, J. M., Hamilton, B. D., Hillmyer, M. A., & Ward, M. D. (2009). Phase behavior and polymorphism of organic crystals confined within nanoscale chambers. Crystal Growth & Design, 9(9), 4766–4777. https://doi.org/10.1021/cg9006185