Dielectric-constant anomaly near the critical solution point in polystyrene + cyclohexane

We present measurements of the static dielectric constant ε near the liquid-liquid critical point in polystyrene + cyclohexane. The data show an anomalous decrease in ε as a function of temperature as the critical temperature is approached from the one-phase region at the critical composition. The anomaly reaches an amplitude of about 7×10^-5 in ε at a few millikelvins from the critical temperature. The data are consistent with the theoretical predictions of a critical exponent for ρ^-1ε of (1-α), where ρ is the density and α is the specific-heat exponent.