Kinetic and mechanistic details of the vesicle-to-rod transition in aggregates of PS310-b-PAA(52) in dioxane-water mixtures

The kinetics and mechanism of the transformation of vesicular aggregates, p repared from the asymmetric, amphiphilic block copolymer polystyrene-b-poly (acrylic acid) in dioxane-water mixtures, into rod-like structures are inve stigated using turbidity measurements and transmission electron microscopy. Since the architecture of these aggregates is known to depend upon the sol vent composition, small jumps in the dioxane content are used to induce the transformation. The transition proceeds with a conservation of the aggrega tion number. This process involves two steps, beginning with the quick coll apse of the vesicles into a `bowtie' structure. This is followed by a slow rearrangement as each bowtie forms a `dumbbell' aggregate and finally a smo oth rod. The relaxation times associated with this morphological change are found to depend upon the initial solvent composition, the magnitude of the dioxane jump, and the initial polymer concentration. (C) 2001 Elsevier Sci ence Ltd. All rights reserved.