Evaluation of solvate and co-crystal screening methods for CL-20 containing energetic materials

ABSTRACT

The difficulty synthesizing new co-crystals has made the development of efficient methods for screening co-formers a high priority. Co-crystals have been realized as a new generation of materials with tuneable solubility, stability, and performance. Energetic co-formers have exceptionally weak intermolecular interactions making selection of co-crystallization method and parameters critical to forming a true co-crystal. COSMO-RS calculations coupled with the COSMOtherm software suite were used to screen common solvents and co-formers for CL-20. The predicted favorable solvates and co-crystal formers were compared to experimentally confirmed solvates and co-crystals to assess the accuracy of the COSMO method for CL-20-based materials. It was found that screening solvents using excess enthalpy and solvent cavity volume were able to predict experimentally confirmed CL-20 solvates. Co-crystal formation was difficult to predict using the COSMO method, highlighting the importance of entropy and solid-state interactions. The selection of good solvents is perhaps the best method for maximizing entropy. Understanding the dependence on entropy for energetic-energetic cocrystal formation coupled with an accurate method for screening co-crystal formation allows for intelligent design of co-crystallization methods.

KEYWORDS:

• CL-20
• COSMO-RS
• solvate
• co-crystal
• prediction

Additional information

Funding

This work was funded by the SDSMT Chemical and Biological Engineering department and the Army Research Office (ARO) in the form of a Multidisciplinary University Research Initiative (MURI) [grant number: W911NF-13-1-0387]. The authors declare no competing financial interest.