Phase Separation and Metallization in C-H Systems Under Warm Dense Conditions

The chemical complexity in C-H systems under warm dense conditions gives rise to a rich phase diagram. Notably, the insulator-to-conductor transition (ICT) has been observed in materials such as methane (CH₄), polystyrene (CH), and polypropylene (CH₂)^1-3. These transitions are critical in high-energy-density (HED) experiments and planetary interiors where it's affected by pressure, temperature, and density. The extreme pressures and temperatures generate thermal and compressional energies comparable to the system’s chemical energy, leading to dissociation, ionization, and metallization. Using laser-driven shocks on samples precompressed in diamond anvil cells (DACs), we investigated the Hugoniot equation of state (EOS) of cyclohexane (C₆H₁₂). Our preliminary analysis reveals a pressure-induced reflectivity increase, reaching values comparable to those observed in conducting hydrogen⁴. Studies^1-3 indicate that similar reflectivity changes correlate with deviations from linearity in the shock velocity (Uₛ)–particle velocity (Uₚ) Hugoniot relation, implying microscopic transformations in these materials.

[1] G. Tabak et al., 2024

[2] D. Kraus et al., 2017

[3] M. A. Barrios et al., 2010

[4] Loubeyre et al., 2012