Volumes of Polar Additives in Aqueous Solutions of the Poly(ethylene oxide)₁₃−Poly(propylene oxide)₃₀− Poly(ethylene oxide)₁₃ Triblock Copolymer at 293 and 301 K

Abstract

Density measurements of poly(ethylene oxide)13−poly(propylene oxide)30−poly(ethylene oxide)13 (L64)−water and alcohol−L64−water systems were carried out at 293 and 301 K. The alcohols studied are propanol to pentanol and 2,2,2-trifluoroethanol (F3EtOH) to 2,2,3,3,4,4,4-heptafluorobutanol (F7BuOH). From the experimental data of the water−L64 binary system as functions of L64 concentration (m C), the partial molar volumes of L64 in the standard state and in the aqueous and micellar phases were calculated. At both temperatures L64 micelle is formed by a core of pure polypropylene oxide units and a hydrated shell of poly(ethylene oxide) units. In the case of the ternary systems, the apparent molar volumes of alcohol (V Φ ,R), at a fixed concentration, as functions of m C were determined. At 293 K, only the premicellar region was studied because the viscosity of the solutions in the micellar region did not permit us to obtain reliable density values. For hydrogenated alcohols as well as for F3EtOH, V Φ ,R as functions of m C are concave curves while for F7BuOH the curve is convex. At 301 K, V Φ ,R of hydrogenated alcohols slightly depends on m C up to the cmc beyond which it increases monotonically with the concentration. The trends of V Φ ,R vs m C for the fluorinated alcohols are peculiar since at ≈0.07 mol kg-1 (micellar region) they show anomalies which are more pronounced the more hydrophobic the alcohol is. The latter were ascribed to structural changes of the aggregates. On the basis of an equation previously reported, from the V Φ ,R data as functions of m C, the partial molar volumes of alcohol in the aqueous and the micellar phases and the distribution constant of alcohol between the two pseudophases were derived.

The solubilisation behaviour of some dichloroalkanes in aqueous solutions of PEO–PPO–PEO triblock copolymers: a dynamic light scattering, fluorescence spectroscopy, and SANS study

“…Such a slope may be correlated to the value of the Setchenov constant 66 which represents the contribution to the free energy for the additive-copolymer interactions in the aqueous phase. Its negative value is consistent with findings 33,37 that hydrophobic additives may induce formation of micelles from the monomeric solutions.…”

“…65,69 Also, the cmc of L64 diminishes in the presence of perfluoroalcohols. 37 Small amounts of halothane lower the onset of aggregation of F88, P84 and P104. 33 As Fig.…”

“…Thermodynamic studies evidenced the affinity of L64 aggregates towards hydrogenated and fluorinated alcohols which are located in the core. 37 Furthermore, we also studied the effect of added surfactants on the structure of Pluronic micelles which dissolve at sufficiently high surfactant concentration 38 and the formation of mixed aggregate between surfactant and unimeric solutions of such copolymers. 39,40 Finally, a predictive molecular thermodynamic theory of solubilisation in block copolymers was formulated by Nagarajan 41 who provided equations for calculating the standard free energy change for the solubilization of hydrocarbons in aggregates of spherical, cylindrical and lamellar shapes.…”

Aqueous solutions of some amphiphilic poly(ethylene oxide)–poly(propylene oxide)–poly(ethylene oxide) triblock copolymers. A thermodynamic study over a wide concentration range at temperatures between 288.15 and 328.15 K

“…An interesting, albeit limited, study has been carried out recently. 21 V f and C p,f values are reported for aqueous solutions of copolymers having molar mass about 5 kg mol À1 and various EO/PO ratios at the three temperatures 278.15, 298.15 and 318.15 K. Recently, our attention was focussed on the volumetric properties of pluronic L64 in water at different temperatures, 22,23 whose values have been found in good agreement with ours. Reliable thermochemical measurements were also performed in a scanning mode over a wide range of temperatures in order to investigate the influence of molar masses and relative PO/ EO mass ratios for selected pluronics and to characterise the thermally induced aggregation process.…”

“…They are a very sensitive way to investigate micellisation and to obtain accurate thermodynamic quantities characterising micellisation processes. [19][20][21][22][23] For example, the existence of three structural regions in the concentration-temperature diagram are defined into the dilute aqueous region. 1,24 With increasing temperature, one successively reaches the more dilute one that contains mainly monomers, then a transition region formed by coexisting monomers and micelles, and finally a composition range where micelles are predominant.…”