Volumes of polar additives in aqueous solutions of the poly(ethylene oxide)(13)-poly(propylene oxide)(30)-poly(ethylene oxide)(13) triblock copolymerat 293 and 301 K

Density measurements of poly(ethylene oxide)(13)-poly(propylene oxide)(30)- poly(ethylene oxide)(13) (L64)-water and alcohol-L64-water systems were car ried out at 293 and 301 K. The alcohols studied are propanol to pentanol an d 2,2,2 trifluoroethanol (F3EtOH) to 2,2,3,3,4,4,4-heptafluorobutanol (F7Bu OH). 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 stand ard state and in the aqueous and micellar phases were calculated. At both t emperatures L64 micelle is formed by a core of pure polypropylene oxide uni ts and a hydrated shell of poly(ethylene oxide) units. In the case of the t ernary systems, the apparent molar volumes of alcohol (V-Phi,V-,(R)), at a fixed concentration, as functions of m(C) were determined. At 293 K, only t he premicellar region was studied because the viscosity of the solutions in the micellar region did not permit us to obtain reliable density values. F or hydrogenated alcohols as well as for F3EtOH, V-Phi,V-R as functions of m (C) are concave curves while for F7BuOH the curve is convex. At 301 K, V-Ph i,V-R of hydrogenated alcohols slightly depends on m(C) up to the cmc beyon d which it increases monotonically with the concentration. The trends of V- Phi,V-R vs m(C) for the fluorinated alcohols are peculiar since at approxim ate to 0.07 mol kg(-1) (micellar region) they show anomalies which are more pronounced the more hydrophobic the alcohol is. The latter were ascribed t o structural changes of the aggregates. On the basis of an equation previou sly reported, from the V-Phi,V-R data as functions of m(C), the partial mol ar volumes of alcohol in the aqueous and the micellar phases and the distri bution constant of alcohol between the two pseudophases were derived.