Light-scattering measurement of concentration fluctuations in phenol-water near its critical point

Abstract

The intensity and spectral width of light scattered by a critical mixture of phenol and water have been measured as a function of temperature both above and below the critical temperature Tc. The temperature dependence of the scattered intensity was fitted to I(T-Tc)-γ for T>Tc and I(Tc-T)-γ′ for T<Tc. Also measured was the ratio RII(ΔT)I(-ΔT) of intensities scattered at a given temperature interval ΔT above and below Tc. The measured values of γ, γ′, and RI were quite close to the predictions of the 3-D lattice gas model. The spectral width Γ was measured using a photon correlation method, and the data were fitted to Γ=DK2A (1+K2ξΓ2), with the diffusion constant D=D0|T-Tc|γ* and ξΓ=ξ0Γ|T-Tc|νΓ The Fixman term K2ξΓ2 (K being the photon momentum transfer) was observed only above the critical temperature. The value of ν and the values of γ* both above and below Tc were in fairly good agreement with the theory of Kadanoff and Swift. The spectral width measurements also provided the ratio RDD(-ΔT)D(ΔT), a quantity for which no theoretical prediction exists. Comparison of this work on phenol-water with that of Swinney and Cummins and others on CO2 near its gas-liquid critical point reveals remarkable similarities between the two systems. © 1971 The American Physical Society.