Vapor−Liquid Equilibria of Aqueous Polymer Solutions from Vapor-Pressure Osmometry and Isopiestic Measurements

Abstract

Water activity data of several binary water + polymer systems were determined experimentally using both vapor-pressure osmometry (VPO) and improved isopiestic methods. The polymers were poly(ethylene glycol) dimethyl ether 250, poly(ethylene glycol) dimethyl ether 500, poly(ethylene glycol) dimethyl ether 2000, poly(ethylene glycol) monomethyl ether 350, poly(ethylene glycol) 200, poly(ethylene glycol) 6000, and poly(propylene glycol) 400. The obtained water activities data were used to calculate the vapor pressure of solutions as a function of concentration. Water activity of all investigated solutions increased with increasing temperature and polymer molar mass. A comparison is given between the vapor−liquid equilibrium data inferred from VPO and isopiestic methods, for different aqueous polymer solutions at 298.15 K, and there is a good agreement between the results of the investigated methods. Furthermore, the segment-based local composition models, nonrandom two-liquid (NRTL), Wilson, and universal quasichemical (UNIQUAC), were used to correlate the experimental activity data.

Phase separation in aqueous solutions of polypropylene glycol and sodium citrate: Effects of temperature and pH

“…water structuring) electrolyte + water systems, as mentioned in our previous work [15]. PPG becomes more hydrophobic by increasing temperature [44] and therefore at higher temperatures the interactions of PPG with surrounding water molecules become weaker, making the exclusion of PPG by the kosmotropic salt and so the formation of ABS easier.…”

“…This is also because the PPG becomes more hydrophobic with an increase in temperature [44]. Thus, by increasing temperature water is driven from the PPG-rich phase to the salt-rich phase, so the PPG concentration at the PPG-rich phase increases, while the salt-rich phase will be somewhat more diluted (i.e.…”

Investigation of Amino Acid–Polymer Aqueous Biphasic Systems

“…As can be seen, for all the investigated systems, an increase in temperature enhances the biphasic region of the phase diagrams in a ratio depending on the solute concentrations, so that, in the polymer rich region, the temperature dependence of the phase diagrams is considerably greater than that in the amino acid rich region, which may be attributed to the thermosensitivity of PPG. PPG becomes more hydrophobic by increasing temperature, 25 and therefore, at higher temperatures, a lower amino acid concentration is required to form an ABS with a certain concentration of polymer, resulting in a binodal curve closer to the axis and a larger biphasic region. It is reasonable to expect that this action should be much stronger at higher concentrations of thermosensitive polymer, and thus, the greater temperature dependence would be observed in the polymer rich region of the phase diagrams in comparison with the amino acid rich region.…”

The Chemical Thermodynamic Models for Calculating the Solvent Activity Coefficient of Semidiluted Aqueous and Nonaqueous Polymer Solutions in Vapor–Liquid Equilibrium

“…Therefore, by using these assumptions, ϕ S i W j in eq 6 can be rewritten as follows: By substituting eq 25 in eq 7 the following is obtained: (26) Moreover, using the above equations and substituting eq 5 in eq 6 we have (27) Hence, based on chemical model, the activity coefficient of solvent can be expressed as (32) and (33) Where α is nonrandomness factor in the range of 0.2 to 0.3 and has no significant effect on the behavior of the model, 2 X is the mole fraction of segment, C is the effective coordination number in the system. 19 A value of r w = 1 was used for solvents, τ mn and E mn are adjustable parameters in NRTL and Wilson models and refer to the interaction between components n and m in solution.…”