Thermodynamics of aqueous polyethylene-glycol (PEG) solutions at 298.15 K: Activity, activity coefficients and application of molecular theories

Osmotic coefficients measured by vapor pressure osmometry are reported for aqueous polyethylene-glycol (PEG-400, PEG-1000, and PEG-4000) solutions. The derived properties such as activity and activity coefficients have been studied as a function of solute concentration. These data along with the partial molar volume data have been analyzed with the help of molecular theories such as Flory-Huggins, McMillan-Mayer, and Kirkwood-Buff. The application of these theories enabled us to obtain second virial coefficients of PEG's, the number of binding sites, chi(12) (Flory-Huggins interaction parameter), and the Kirkwood-Buff (KB) integrals, defined by the equation: Gij = integral(infinity)(0) (gij - 1)4 pi r(2)dr. The highlight of the work is the observation that microheterogeneity in solution increases as the chain length of solute molecule increases [estimated through mean square concentration fluctuation N <(Delta x)(2)> and non-ideality (F) parameters], confirming the concept of solute association through hydrophobic interactions in aqueous solutions. (C) 2013 Elsevier B.V. All rights reserved.