Elastic Scattering of Light by Binary Mixtures above and below the Critical Solution Temperature. I. Methanol Cyclohexane

An investigation was made of the light-scattering properties of the methanol–cyclohexane binary system in the one-phase region above the critical solution temperature Tc and in the two-phase region below Tc. Measurements were made down the critical isochore for T > Tc and along the methanol-rich side of the coexistence curve for T < Tc. A modification of the Ornstein–Zernike–Debye theory of light scattering was found to be in reasonable agreement with the results for T < Tc. The Debye parameter “l” was 14.5 ± 0.5 Å above Tc and 14.0 ± 1.3 Å below Tc. The ratio of the extrapolated zero-angle inverse intensity at any ΔT below Tc to that quantity at the same ΔT above Tc was 3.6. The persistence length for fluctuations below Tc as determined by the Debye theory was of the same order of magnitude as the thickness of the binary interface.