Quantification of thermodynamics of aqueous solutions of poly(ethylene glycols): Role of calorimetry

A correlation based on generalized Flory-Huggins model, which relates the activity data of aqueous poly(ethylene glycol) (PEG) solutions at low temperatures to the binodal curve in the LCST region, has been developed. The temperature dependent parameters of the model are estimated by regression of the experimental data of the enthalpy of mixing of aqueous PEG solutions, obtained using isothermal titration calorimetry. The temperature independent parameters are estimated from the data of the activity of PEG solutions at a single temperature. An attempt to develop a similar correlation based on the hydrogen bond model has been unsuccessful. It is also shown that the correlation based on the activity data alone, does not have the ability to predict the binodal curve and the use of the enthalpy data is essential for this purpose.