Critical Opalescence and Electric Field Effect in Cyclohexane-Methanol

Critical fluctuations in a binary mixture, cyclohexane-methanol, are studied by measuring the intensity of the Rayleigh scattering. Measurements are made along the critical isochore above T c , and along the methanol-rich side of the coexistence curve below T c . Critical exponents and the zero temperature correlation lengths are determined as γ=1.27±0.06, γ'=1.14±0.10, ν=0.65±0.03, ν'=0.58±0.04, ξ o =4.1±0.5 Å, and ξ' oM =6.2±1.2 Å, where ξ o and ξ' oM are respectively the zero temperature correlation lengths above and below T c . The scattering intensity shows a decrease when AC electric field is applied. The decrease | Δ I |/ I ={ I ( k , E )- I ( k , 0)}/ I ( k , 0), where E is the field strength and k the scattering vector, is determined in the temperature range 1×10 -5 ≤ t ≤5×10 -2 , where t is the reduced temperature. The maximum value of | Δ I |/ I was 0.65 at E =700 V p-p /cm. The field strength dependence of | Δ I |/ I is interpreted by applying the formula which explains the intensity of the Rayleigh scattering due to the fluctuations of the orientation of a director n o in nematic liquid crystals.