Characterization of defects and role of molecular flexibility in cyclotrimethyelenetrinitramine (RDX)

Abstract

Molecular crystals typically comprise irregularly shaped molecules packed in low symmetry crystalline configurations. The anisotropic nature of bonding and low cohesive energies are responsible for their complex and novel mechanical, electronic, vibrational, and optical properties. Owing to their importance in pharmaceutical, electronic, energetic and food materials, this class of crystals has fostered myriad investigations over the last century. This dissertation focuses on a specific molecular crystal, α-cyclotrimethylene trinitramine (α-RDX), which is a commonly used energetic material. There are three investigation tracks in this work. First, a type of point defect that is specific to molecular crystals, called orientational defect, is presented and studied for α-RDX. Secondly, since this molecular crystal comprises flexible molecules, the influence of such flexibility on elastic-plastic properties of α-RDX is quantified. Thirdly, the Peierls free energy barriers for the motion of dislocations in α-RDX is estimated using a novel umbrella sampling based technique.