Dynamics of Block Copolymer Micelles in Aqueous Solution

Abstract

The dynamics of aqueous micelles of triblock EnPmEn copolymers (En = poly(ethylene oxide); Pm = poly(propylene oxide)) is investigated. It is shown on a theoretical basis that the amplitude of the relaxation process associated with the EnPmEn micelle formation−breakup must go from negative to positive upon increasing temperature in relaxation experiments using the temperature-jump (T-jump) method with light scattering detection. New experimental T-jump results for solutions of two different EnPmEn copolymers clearly confirm this prediction. These results do not support the claim made by Kositza et al. [Langmuir 1999, 15, 322; Macromolecules 1999, 32, 5539] that the temperature at which the amplitude of the slow process observed in T-jump experiments goes through zero corresponds to a change in the nature of this process, from micelle formation−breakup below this temperature to micelle clustering above this temperature.