Interpretation of correlation length by small-angle X-ray scattering experiments on fluids near critical point

Small-angle X-ray scattering from fluids near the critical point, such as CHF3, CO2, Xe, and H2O, was analyzed using an intensity distribution function of fluctuating structures, D(R), in order to investigate the inhomogeneity in these fluids. It was found that the function D(R) ∝ 1/(R4 + L4) could provide a good approximation of the intensity distribution functions of the fluctuating structures in the fluids. The Ornstein–Zernike correlation length (ξ) was found to be related to the half width at half maximum (L) of D(R): ξ was approximately 5/18 of L.