Nitroxide-Mediated Polymerization-Induced Self-Assembly of Block Copolymers at the Surface of Silica Particles: Toward New Hybrid Morphologies

摘要

Silica/polymer latexes with concentric core-shell-corona, half-capped, snowman-like vesicular, tadpole- and centipede-like morphologies have been produced by nitroxide-mediated polymerization-induced self-assembly (PISA) performed in the presence of aqueous suspensions of colloidal silica. A hydrosoluble brush-like PEO-based macroalkoxyamine (P[(poly(ethylene oxide) methyl ether methacrylate)(12)-co-styrene]-SG1, M-n = 11 700 g mol(-1) and M-w/M-n = 1.11) was first adsorbed onto the surface of submicronic silica particles. The obtained suspension was then used in the emulsion polymerization of n-butyl methacrylate with 8 mol % of styrene. This led to the formation of amphiphilic block copolymers (BCPs) that self-assembled in situ at the silica surface into well-defined hybrid nano-objects of various morphologies, in agreement with the principles of polymerization-induced micellization. The influence of the pH was more specifically investigated, using silica particles of different size ranging from 30 to 230 nm. This parameter was shown to have a significant effect on particle morphology. Indeed, while multipod-like particles were obtained below pH 6 regardless of the silica particle size, polymerizations conducted at higher pH values led to unconventional morphologies that have never been reported before. Silica-armored fibers and/or vesicles were obtained for the smallest silica particles (D-n = 30 nm) whereas larger silica beads (D-n = 230 nm) predominantly led to core-shell particles. More interestingly, the use of an intermediate silica particle size (D-n, = 136 nm) led to a complex mixture of kinetically trapped copolymer morphologies. For the first time, cryo-electron tomography (cryo-ET) of the sample provided direct observation of the 3D structures and furthermore gave insights into the self-assembly process as intermediate morphologies were also captured.