Abstract
The concentration and temperature dependences on micelle formation by a polystyrene- block-poly(ethylene/propylene) copolymer in several ketones (methyl-ethyl ketone, methyl propyl ketone, diethyl ketone, methyl isobutyl ketone, dipropyl ketone, 5-methyl-2-hexanone and 5-methyl-3-heptanone) are studied by laser light scattering and viscometry. No micelles were detected in solutions of 5-methyl-3-heptanone. The standard Gibbs energy, ΔG°, the standard enthalpy, ΔH°, and the standard entropy, ΔS°, of micellization were estimated from the dependence of the critical micelle temperature on concentration. The values of ΔG°, ΔH° and ΔS° were negative for all ketones studied. ΔG° and ΔH° depend on the polar character of the ketone. The weight average molar mass, second virial coefficient and apparent radius of gyration have been calculated from the standard Zimm plots obtained. Huggins and Kraemer equations have been employed to determine the limiting viscosity number of the micelles. The micelles formed in ketone solutions show larger association numbers and densities than those formed in n-alkane solutions.
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