Control of Structure in Multicompartment Micelles by Blending μ-ABC Star Terpolymers with AB Diblock Copolymers

Abstract

A unique multicompartment micelle, herein referred to as a “hamburger” micelle, was formed from a binary mixture of spherical micelles, formed from polyethylethylene- b -poly(ethylene oxide) (EO) diblock copolymers, and segmented wormlike micelles, formed from μ-(polyethylethylene)(poly(ethylene oxide))(polyperfluoropropylene oxide) (μ-EOF) mikto-arm star terpolymers. Cryogenic transmission electron microscopy (cryoTEM) and dynamic light scattering (DLS) were used to characterize the evolution of micelle structure and size distribution as a function of annealing time, over the course of several months. Considering the extremely low critical micelle concentration of these amphiphilic copolymers, we propose that the micelle evolution was due to a collision/fusion/fission process. The long segmented wormlike micelles first fused with EO spherical micelles, followed by fission to progressively shorter micelles, which finally evolved into more stable hamburger micelles. Three elementary “reactions” were used to describe these structural transitions. Multiple fusions of spherical micelles into already formed hamburger micelles sometimes resulted in the formation of asymmetric hamburger micelles and also induced a micelle shape change from prolatelike to more oblatelike ellipsoids. A binary blend of μ-EOF miko-arm star terpolymer with EO diblock in the bulk prior to micellization did not generate new intermediate micelle structures, presumably because of phase separation between μ-EOF and EO during the film-casting process.