Studies of the Effect of Urea on PEG-4000 Polymer–Water Interactions at 298.15 K

Abstract

Osmotic coefficient measurements have been reported for binary aqueous solutions of urea (0.11400 to 1.03192 mol·kg–1) and ternary aqueous solutions containing a fixed concentration (0.10065 mol·kg–1) of polyethylene glycol 4000 (PEG-4000) and various concentrations of urea (0.03882 to 0.70509 mol·kg–1) at 298.15 K using vapor pressure osmometry. For the binary (urea + water) system, using experimental osmotic coefficient data, the activity and activity coefficient of urea and water are calculated, and further activity data are processed to obtain the Gibbs free energy change of mixing and excess Gibbs free energy change of mixing. The water activities for the studied ternary system (water + 0.10065 mol·kg–1 PEG-4000 + urea) were calculated and used to obtain the activity coefficient of PEG-4000 and urea. The transfer free energy changes of PEG-4000 from water to aqueous urea solutions (ΔG tr 1) and that of urea from water to aqueous PEG-4000 solutions (ΔG tr 2) have been calculated using the activity data. The pair and triplet interaction parameters are estimated by applying McMillan–Mayer theory of virial coefficients to the data of transfer Gibbs free energy. The salting constant (k s) value and equilibrium constant (log K) value have been estimated for PEG-4000–urea complexation at 298.15 K. All these results are discussed in light of binding equilibria and water structure alteration concepts. It has been shown that the hydrophilic interaction of urea with the backbone of a polymer is also contributing to solution properties.

Vapor–Liquid Equilibrium of Aqueous Urea Solution from Dynamic Vapor Sorption Measurements at 283.15–343.15 K

“…A comparison between the water activity data inferred from the DVS technique and isopiestic method at 298.15 K is displayed in Figure for aqueous solutions of urea. In Figure , comparisons of the experimental water activity data measured in this work with available data obtained by the VPO method have been made for aqueous urea solution at 298.15 K . As can be seen, there is good agreement between the results obtained in this work and those taken from the literature.…”

“…In Figure 2, comparisons of the experimental water activity data measured in this work with available data obtained by the VPO method have been made for aqueous urea solution at 298.15 K. 24 As can be seen, there is good agreement between the results obtained in this work and those taken from the literature. Also, due to the capability and limitations of VPO and DVS methods, it seems that using the VPO technique for measuring the water activity of the aqueous urea solutions at low concentration of solute and the DVS method for those of concentrated aqueous urea solutions can provide reliable water activity data over a wide range of urea concentrations for these solutions.…”

“…Kushare value of some dilute aqueous urea solution in the concentration range 0.11400−1.03192 mol•kg −1 at 298.15 K. 24 It was found that in this range of urea concentration and temperature, increasing the solute concentration reduces the osmotic coefficient and water activity coefficient. 24 The hydrolysis of urea has always been of interest, and different reaction processes have been proposed for that. It has been revealed that temperature plays a significant role in the intermediate and final reaction products in this system.…”

“…At 298.15, 303.15, and 313.15 K increasing the urea concentration has different effects on the osmotic coefficient of the solutions and at T > 313.15 K, an upward trend with increasing urea concentration was indicated. Kushare et al determined the osmotic coefficient value of some dilute aqueous urea solution in the concentration range 0.11400–1.03192 mol·kg –1 at 298.15 K . It was found that in this range of urea concentration and temperature, increasing the solute concentration reduces the osmotic coefficient and water activity coefficient …”

“…The isopiestic method has been the most commonly used technique to measure the solvent activity coefficient of aqueous urea solutions at 25 °C. ,, The freezing point depression is another technique that has been applied in the past to measure the osmotic coefficients of binary aqueous urea solutions. ,, Recently, solvent activities and osmotic coefficients of urea water solutions have been measured by the VPO method in a wide range of temperatures and concentrations. − In either of these methods, it has been tried to report accurate data and compares obtained information with previous works.…”