Measurement of activity of water in aqueous poly(ethylene glycol) solutions (Effect of excess volume on the Flory-Huggins chi-parameter)

Activities of water are reported for aqueous solutions of poly(ethylene gly col) (PEG) with number average molecular weights of 300, 400, 4000, and 600 0 are measured at 35, 45, 55, and 65 degrees C and at various concentration s from 0 to 40 wt % of PEG using vapor-pressure osmometery. A cubic equatio n in terms of PEG concentrations is sufficient for correlation of activitie s. Using measured activities, the Flory-Huggins interaction parameters have been calculated. The effect of temperature, molecular weight of PEG and it s concentration, and volume change upon mixing on interaction parameter hav e been considered. Ignoring the volume change of mixing can lead to an aver age error of 2.5% with a maximum error of 5.3%.