The equation of state of polytetrafluoroethylene to 80 GPa

Hugoniot data for polytetrafluoroethylene (PTFE) have been reported. These data can be fitted by two linear u_s–u_p Hugoniots which indicate the existence of a phase change. As usual for polymers, a linear low‐pressure u_s–u_p fit does not extrapolate to the zero‐pressure bulk sound‐speed. The phase transition occurs at ∼34 GPa and a compression of 0.396. To investigate this high‐pressure phase transition, shock‐recovery experiments were performed. The recovery system used is described. The recovered samples indicate the high‐pressure phase transition is a dissociation reaction into carbon and gaseous fluorocarbons. Release isentropes at various pressures have been measured using the ASM probe. From these measurements, the variation of the Grüneisen parameter was calculated for states both on and off the Hugoniot. The Grüneisen parameter on the Hugoniot monotonically increased from its initial value until the phase transition where it dropped slightly and then continued to increase with further increase in pressure. The Grüneisen parameter has been theoretically modeled in the solid phase and the model helps to explain some of these unusual experimental results.