Measuring the structure and equation of state of polyethylene terephthalate at megabar pressures

We present structure measurements of biaxially orientated polyethylene terephthalate (PET, (C10H8O4)n , also called mylar) shock-compressed to (155+/-20) GPa and (6000+/-1000) K using in situ X-ray diffraction. Comparing to density functional theory molecular dynamics simulations, we find a highly correlated liquid that exhibits a temperature signficantly lower than predicted by some equation-of-state tables, which underlines the influence of complex chemical interactions in this regime. Indeed, at the inferred temperature and pressure, formation of nanodiamonds may be expected as recently observed in polystyrene at similar conditions. While some hints of diamond formation from PET are visible in the diffraction data, the strong liquid correlations prevent a conclusive statement as to whether diamonds are formed inside the sample volume.