Liquid Structure of Shock-Compressed Hydrocarbons at Megabar Pressures

Area of Science:

• Materials Science
• Condensed Matter Physics
• Physical Chemistry

Background:

• Shock compression experiments probe materials under extreme conditions.
• Understanding the ionic structure of hydrocarbons is crucial for various applications.
• Previous predictions suggested complete carbon-hydrogen demixing under high pressure.

Purpose of the Study:

• To investigate the ionic structure of shock-compressed hydrocarbons (polystyrene, polyethylene).
• To validate ab initio simulations for modeling mixed samples under extreme conditions.
• To assess the role of diffraction in diagnosing carbon-hydrogen demixing.

Main Methods:

• Shock compression of polystyrene and polyethylene to pressures up to 190 GPa.
• In situ X-ray diffraction using an X-ray free electron laser (XFEL).
• Comparison of experimental data with ab initio simulations.

Main Results:

• Rapid melting of hydrocarbons was induced by shock compression.
• Reliable diffraction data were obtained in a single shot for low-Z samples.
• Experimental data showed good agreement with ab initio simulations.
• Complete carbon-hydrogen demixing was excluded at probed conditions.

Conclusions:

• Ab initio simulations are capable of modeling mixed samples with complex interparticle bonds.
• Simpler models may not be sufficient for describing these states.
• Diffraction alone is not always a sufficient diagnostic for carbon-hydrogen demixing.