Static inhomogeneity of supercritical ethylene studied by small-angle X-ray scattering

Abstract

Abstract Small-angle X-ray scattering (SAXS) experiments for supercritical C2H4 were carried out, to study its density fluctuation and correlation length, which are quantitative descriptions of the inhomogeneity of molecular distribution. Except for thermodynamic states near the critical point, the density fluctuation from SAXS experiments is in very good agreement with the one calculated from a new state equation. For investigation on the substance dependence of the inhomogeneity in supercritical states, the results were compared with our previous ones of CO 2 , CF 3 H and H2O. The density fluctuation and correlation length for C2H4 show fairly similar behaviors to those of supercritical CO 2 , CF 3 H as a function of reduced density ρr=ρ/ρc and reduced temperature Tr=T/Tc. On the other hand, characteristics for inhomogeneity of supercritical H2O are different from those of others. Good correspondence of static inhomogeneity and dynamic one in supercritical C2H4 is revealed, by comparing the fluctuation from SAXS with its correlation time from dynamic light scattering experiments.