Capturing Polymer Chain Compression and Shock Driven Decomposition of Polytetrafluoroethylene During Dynamic Shock Compression with in Situ X-Ray Diffraction

Observations of unit cell compression or decomposition during dynamic shock loading requires the implementation of a probe capable of penetrating an opaque and evolving sample at elevated pressures and temperatures. By pairing synchrotron generated high energy X-rays and gas gun driven plate impact, we were able to study the evolution of the structure in polytetrafluoroethylene (PTFE) at pressures spanning 1.84–52.9 GPa. Under the planar, one-dimensional, shockwave, the polymer was forced into an anisotropic conformation, in which the polymer chains assembled parallel to the shockwave. PTFE initially has a hexagonal crystal structure (Phase IV), once it was compressed above ~0.5 GPa it had a conformational change to the orthorhombic crystal structure (Phase III). The compression of the polymer chains was observed by X-ray diffraction, where the PTFE (110) peak shifted to higher q with increased pressure; polymer chain compression was still observed at 30.0 GPa. The highest pressure shot, at 52.9 GPa, above the reactants to products transition region, showed no new carbon species formation within the given time window and q -range. By following the orthorhombic lattice diffraction peak, we were able to calculate the Hugoniot loci of the crystalline and amorphous parts for each dynamic event (LA-UR-22-31436).