Cloud-point measurements for (water plus poly(ethylene glycol) plus salt) ternary mixtures by refractometry method

The cloud-point temperatures and phase separation of (water + poly(ethylene glycol) + salt) ternary systems were studied by the refractometry method. The salts were K3PO4, K2HPO4, Na2HPO4, or Na2CO3. The phase separation was also observed by visual inspection. Differences between the measured cloud point using the refractometry method, and visual inspection was up to +/- 1 degrees C. The measured cloud-point temperatures are compared with those obtained by viscometry and laser beam scattering methods. These comparisons indicate complete agreement between the different methods for cloud-point temperature measurements for the (water + poly(ethylene glycol) + salt) ternary system. The salt-included liquid-liquid separation is studied by using the Flory-Huggins polymer solution theory. A simple linear temperature composition-dependent interaction parameter (chi) was applied for correlation of the measured cloud-point temperatures. The comparison between measured and correlated cloud-point temperatures indicates that average absolute deviation is less than 0.61 degrees C. Therefore, the Flory-Huggins model was successfully applied to determine the phase separation conditions of the ( water + poly(ethylene glycol) + salt) ternary systems.