Implementation of a Double Stage Compression Technique to Study Structural Transformation Mechanisms in Aromatic Polymers

Many aromatic polymers undergo a shock-induced transformation above ~15 GPa, often with significant volume collapses. While the mechanisms responsible for these transformations remain unclear due to challenges in combining in situ characterization with dynamic compression, static compression is a viable alternative. In-situ energy dispersive X-ray diffraction experiments were carried out at room temperature and up to 32 GPa with a double stage compression technique developed at sector 16 of the Advanced Photon Source (APS) in a large-volume Paris Edinburgh press using polyurea, an amorphous aromatic elastomer used in armor applications. Signatures of a transformation were observed in the total structure factors and pair distribution functions between 11-16 GPa. The transformation appears to be driven by a disruption in the intermediate range order arising from interchain distances and the subsequent formation of cross-linkages between neighboring chains. Potential improvements to the technique, including Monte Carlo refinements of a large-box atomic model, will be discussed.