KCl-Induced Phase Separation of 1,4-Dioxane + Water Mixtures Studied by Electrical Conductivity and Refractive Index

Abstract

Salt-induced phase separation of 1,4-dioxane (D) + water (W) with KCl has been investigated by measuring the electrical conductivity (κ) and the refractive index (n) along the coexisting curve in the vicinity and far from the lower critical solution temperature (LCST) using a conductometer and a refractometer. By visual method, the lower critical temperature (Tc) was determined to be (311.032 ± 0.015) K with the mole fraction of dioxane on a salt-free basis: x′D = nD/(nD + nW) = 0.295 ± 0.002. The conductivity and refractive index were carried out in the range of 0.010 K < (T − Tc) < 17.500 K. Critical values were fitted and compared with those predicted by models proposed in the literature. The electrical conductivity and refractive index coexistence curve data were analyzed to determine the critical exponent (β) associated with the coexistence curve. The results show that those (κ and n) constitute good order parameters as valid as the volume fraction. In the neighborhood of the LCST (T/Tc − 1 < 3·10−2), the critical exponent obtained by the two techniques agrees with the scaling law prediction. The KCl salt at the saturation facilitates the formation of the molecular correlations, and the phase separation takes place in the electrolyte.