Confinement-induced shift of thermodynamic response and energetic heterogeneities in supercritical fluids

Supercritical fluids are widely employed in energy-related processes involving nanoporous environments, where thermodynamic response functions such as heat capacity and compressibility govern heat transfer and transport. However, nanoscale confinement alters the response-function maxima associated with the Widom line, affecting the effective operating regimes of confined supercritical fluids. In this study, molecular dynamics simulations are performed to investigate how confinement modifies the thermodynamic response of supercritical fluid in slit pores. The results show that confinement induces systematic shifts of the Widom line toward lower temperatures. Layer-resolved analysis of the in-plane structure factor further reveals spatial heterogeneity in local compressibility across the pore, indicating a redistribution of thermodynamic response under confinement. Energetic analysis demonstrates that the bulk scaling relation between cluster size and cohesive energy breaks down due to confinement-induced morphological anisotropy, with large, flattened clusters preferentially forming near the walls and small clusters dominating the pore center. These findings establish a microscopic link between nanoscale confinement and the shift of thermodynamic response functions in supercritical fluids.