The Elastic Constants and Related Mechanical Properties of the Monoclinic Polymorph of the Carbamazepine Molecular Crystal

Polymorphism is the property of a compound to crystallize in two or more crystalline phases containing different arrangements and/or conformations of the molecules in the crystal lattice. The Phenomenon of polymorphism is a major issue in the pharmaceutical industry especially in relation to drug uptake in the body, tablet processing and growth. This has led to considerable interest in predicting and understanding properties of drug polymorphs, and more recently the mechanical properties of the polymorphs. In this work, Brillouin scattering is used to probe the acoustic phonons of the monoclinic ($P$2$_{1}$/$c)$ polymorph of the drug, carbamazepine (CBZ). By sampling a variety of acoustic phonons, the complete elastic constant tensor has been determined for this CBZ polymorph. The observed trend in the elastic constants: C$_{11}<$ C$_{22}\sim $C$_{33}$ is qualitatively associated with the crystal growth pattern seen in CBZ. Investigation into the anisotropy of the intermolecular interactions has been investigated further by calculation of linear compressibilities.