Chain Overcrowding Induced Phase Separation and Hierarchical Structure Formation in Fluorinated Polyhedral Oligomeric Silsesquioxane (FPOSS)-Based Giant Surfactants

The self-assembly behaviors of fluorinated polyhedral oligomeric silsesquioxane (FPOSS)-based giant surfactants, consisting of an FPOSS cage and a polystyrene-block-poly­(ethylene oxide) (PS-b-PEO) diblock copolymer tail, are studied in the bulk. The tethering point of the FPOSS cage on the PS-b-PEO diblock copolymer chain can be controlled precisely either at the end of the PS block or the junction point between the PS and PEO blocks, resulting in topological isomer pairs with almost identical chemical compositions but different architectures. Phase separation between the FPOSS head and the block copolymer tail creates a spatially confined environment for the PS-b-PEO component, which are uniformly end- or junction-point-immobilized on the FPOSS layer, providing a unique model system to study phase behaviors and chain conformation of tethered diblock copolymer in the condensed state. The polymer tails are highly stretched because the cross-sectional area of FPOSS head is smaller than that of the unperturbed block copolymer tail, which facilitates further phase separation between the low molecular weight PS and PEO blocks and leads to the formation of hierarchical lamellar structures among three mutually immiscible components.