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

Theself-assembly behaviors of fluorinated polyhedral oligomeric silsesquioxane(FPOSS)-based giant surfactants, consisting of an FPOSS cage and apolystyrene-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 atthe end of the PS block or the junction point between the PS and PEOblocks, resulting in topological isomer pairs with almost identicalchemical compositions but different architectures. Phase separationbetween the FPOSS head and the block copolymer tail creates a spatiallyconfined environment for the PS-b-PEO component,which are uniformly end- or junction-point-immobilized on the FPOSSlayer, providing a unique model system to study phase behaviors andchain conformation of tethered diblock copolymer in the condensedstate. The polymer tails are highly stretched because the cross-sectionalarea of FPOSS head is smaller than that of the unperturbed block copolymertail, which facilitates further phase separation between the low molecularweight PS and PEO blocks and leads to the formation of hierarchicallamellar structures among three mutually immiscible components. [ABSTRACT FROM AUTHOR]