Liquidlike behavior of supercritical fluids.
The high frequency dynamics of fluid oxygen has been investigated by inelastic x-ray scattering, at high pressures and room temperature. In spite of the markedly supercritical conditions (T approximately 2Tc, P>10(2)Pc), the sound velocity exceeds the hydrodynamic value of about 20%, a feature which is the fingerprint of liquidlike dynamics. The comparison of the present results with literature data obtained in several fluids allow us to identify the extrapolation of the liquid-vapor-coexistence line in the (P/Pc, T/Tc) plane as the relevant edge between liquidlike and gaslike dynamics. More interestingly, this extrapolation is very close to the non-metal-metal transition in hot dense fluids, at pressure and temperature values as obtained by shock wave experiments. This result points to the existence of a connection between structural modifications and transport properties in dense fluids.
Gorelli
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Research Center SOFT-INFM-CNR, Università di Roma La Sapienza, I-00185, Roma, Italy.
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