MICELLIZATION OF A POLYSTYRENE-BLOCK-POLY(ETHYLENE PROPYLENE) COPOLYMER IN N-ALKANES .1. THERMODYNAMIC STUDY

Light scattering was used to determine the dependence of the critical micelle temperature on concentration for solutions of a polystyrene-block-poly(ethylene/propylene) copolymer in n-hexane, n-heptane, n-octane, n-decane, and n-dodecane. The results were used to estimate the standard Gibbs energy, DELTA-G-degrees, the standard enthalpy, DELTA-H-degrees, and the standard entropy, DELTA-S-degrees, of micellization. The values of DELTA-H-degrees were large and negative and were markedly dependent on the carbon number for the lower n-alkanes. The values of DELTA-G-degrees are negative for all n-alkanes studied. The variation of DELTA-G-degrees with the number of carbons in the n-alkane chain depends on the temperature, showing a maximum for n-octane at 85-degrees-C. At 25-degrees-C, DELTA-G-degrees becomes more negative as the n-alkane carbon number increases, showing a marked decrease between n-heptane and n-octane. The different behaviors for the studied n-alkanes are explained by taking into account the differences in the polystyrene/n-alkane interactions.