Key words: critical phenomena, Widom line, optical diagnostic methods, pair correlation function
A fundamental problem of optical diagnostics of the supercritical fluid structure and its statistical properties in the vicinity of the Widom line is considered. To perform the diagnostic procedure one needs some techniques to build the connection between the peculiarities of optical measurement data to the peculiarities of fluid state. A brief review of the results obtained over the past 10 years on the problem of Widom lines in nonpolar supercritical media is presented. Data on the measurements of the nonlinear refractive index and on the Rayleigh light scattering intensity in the region of the Widom line in CO2 is considered in detail. It is demonstrated that these data can serve as the basis for reci procally complementary methods for optical diagnostics of supercritical fluid state. As an example, a small angle light scattering data were used to find the pair correlation function of supercritical CO2. The temperature dependence of the latter differs fundamentally from the temperature dependence of the Ornstein—Zernike pair correlation function. It is noted that the method based on the measuring of the Rayleigh scattering intensity is of a general nature and it can be applied to any random molecular media, including the planet atmosphere.
doi:10.34984/SCFTP.2022.17.2.002