Experimental and modeling evidence for structural crossover in supercritical CO_{2}

Area of Science:

• Thermodynamics
• Materials Science
• Chemical Physics

Background:

• Supercritical fluid physics is less understood than subcritical liquid behavior.
• The supercritical phase diagram of carbon dioxide remains largely unexplored.
• Existing knowledge gaps hinder applications and fundamental understanding of supercritical states.

Purpose of the Study:

• To investigate the structural properties of supercritical carbon dioxide.
• To identify and characterize phase transitions or crossovers in supercritical CO2.
• To elucidate the behavior of fluids beyond their critical point.

Main Methods:

• Neutron scattering experiments were employed to probe atomic/molecular structure.
• Molecular dynamics simulations were utilized to model fluid behavior.
• Combined experimental and computational approaches provided a comprehensive analysis.

Main Results:

• A significant structural crossover was identified at the Frenkel line in supercritical CO2.
• This crossover was observed at pressures up to 14 times the critical pressure.
• Key features of the structure factor and pair distribution functions showed distinct changes, indicating altered fluid structure.

Conclusions:

• The study demonstrates a distinct structural crossover in supercritical carbon dioxide at the Frenkel line.
• This finding provides crucial insights into the under-explored physics of supercritical states.
• The results bridge the gap between subcritical and supercritical fluid behavior, particularly for CO2.