It has been well-known that aqueous solutions of poly(ethylene oxide) (or poly(ethylene glycol)) (PEO) are clear in a low temperature range but show clouding points due to phase separation behavior at rather high temperatures close to 100 °C slightly dependent on its average molar mass and concentration. We carried out extremely high frequency dielectric relaxation measurements up to 50 GHz over a temperature range from 10 to 70 °C to determine the temperature dependence of a hydration number per ethylene oxide monomer unit (mEO) in PEOs with the average molar masses higher than 3000. The obtained mEO was a constant value of ca. 4 in a temperature range lower than 30 °C and decreased rather gradually and approached ca. 2 at 70 °C. The temperature dependence of mEO, hydration/dehydration behavior, confirmed in this study should be the essential reason for the phase separation behavior observed at high temperatures. The hydration/dehydration behavior observed in this study was compared with that reported pr...

Temperature-Dependent Hydration/Dehydration Behavior of Poly(ethylene oxide)s in Aqueous Solution

The osmotic coefficients and densities of aqueous and CCl4 solutions involving 18-crown-6 (18C6) as solute in the concentration range 0.1 to 2.0 m at 25 °C were measured. The data obtained is used to calculate activities of solvent and activity coefficient of solute and solvent at 25 °C as a function of concentration. It has been observed that activity coefficient of 18C6 increases with increase in concentration of 18C6 while the reverse is true for CCl4 solutions. Using the partial molar volume of the solute at infinite dilution, the solute−solvent cluster integral values were evaluated which yielded information on solute−solvent interaction. Application of McMillan-Mayer theory enabled us to obtain second and third virial coefficients for solute, which have been decomposed into attractive and repulsive contributions to solute−solute interactions. These are compared with other solutes such as sucrose, glucose, urea, etc. On the basis of attractive and repulsive contributions to solute−solvent and solute−...

Studies of Osmotic and Activity Coefficients in Aqueous and CCl4 Solutions of 18-Crown-6 at 25 °C

Thermodynamic studies for aqueous solutions involving 18-crown-6 and alkali bromides at 298.15 K

The near-infrared difference spectra of 18-crown-6 in aqueous solutions have been obtained in the 1350−1650 nm region. Resolution of the difference spectra yielded the spectra of hydrated 18-crown-6 molecule and with the help of density data has allowed the determination of hydration numbers of 18-crown-6 at different concentrations (0.5−4 m). The hydration number obtained at 1 m concentration of 18-crown-6 is about ∼20, while at higher concentrations the value is around 4. These results have been interpreted in terms of hydrophobic hydration of 18-crown-6 in the dilute concentration region, resulting in clathratelike equilibria, while at higher concentrations, four water molecules remain hydrogen-bonded to the crown ether ring having D3d conformation. These complexed water molecules have been further differentiated into two types: (i) two water molecules doubly hydrogen-bonded (bridging) to the crown ether oxygen atoms and (ii) the other two singly hydrogen-bonded to the remaining oxygen atoms and rapidl...

G.S. Gokavi

Papers

Studies of partial molar volumes of 18-crown-6 in water at 25 C