Properties of aqueous salt solutions of poly(ethylene oxide): Thermodynamic quantities based on viscosity and other measurements

Abstract

AbstractA previous study of poly(ethylene oxide) (PEO) in aqueous salt solutions has been extended to incorporate cloud‐point measurements in potassium thiocyanate solutions (salt concentration range 3.3–3.8M where salting out occurs) and, particularly, viscosity measurements. A few osmoticpressure measurements were made and molecular weights (∼2 × 104) from gel‐permeation chromatography (GPC) compared. The theta temperature for PEO in water from cloud points was found to be 369 ± 3°K. An empirical linear relation has been found for sodium and potassium salts between the finite change of theta temperatures with change in ionic strength, δθ/δI, and (v3 − v̄3), the difference between the molar van der Waals volume and the partial molar volume of the salt. Values of the Huggins constant k′ are less than 0.5 for PEO in pure water at 303.2°K, indicating a good solvent, whereas in salt solutions they vary from 0.59 to 1.14 in nontheta solvents. They and other findings are attributed to binding of salt to the polymer and to water structure breaking. Kraemer's constants k″ were also determined: k′ − k″ = 0.5 for PEO in pure water, and for aqueous salt solutions of PEO, k′ − k″ = 0.666 at 298°K. Values of K0(= M−1/2[η]θ) with M = 2 × 104 were found to very with salt type (valence)—mean values of 103 K0/dlg−1 with number of observations in brackets are 1:1, 1.19 (2); 1:2, 1.45 (3); 2:2, 1.75 (3). Unperturbed dimensions 〈r2〉 vary from 11.0 to 12.6 nm from 1:1 to 2:2 salts. Values of the characteristic ratio Cn, the steric parameter σ, and the enthalpy and entropy of dilution parameters χH and χS have also been calculated.