Phase Behaviors of Multi-tailed B_(2)AB_(2)-Type Regio-isomeric Giant Surfactants at the Columnar-Spherical Boundary

We report herein the precision synthesis and phase behaviors of multi-tailed B_(2)AB_(2)-type regio-isomeric giant surfactants consisting of a hydrophilic polyhedral oligomeric silsesquioxane(POSS)head tethered with four hydrophobic polystyrene(PS)tails.The synthesis was accomplished through two sequential"click"reactions to give a series of regio-isomeric giant surfactants S2DS2(where S is short for PS tails and D for hydroxyl-functionalized POSS)in para-,meta-,and ortho-configurations.Their phase structures and phase be-haviors at the columnar-spherical boundary were investigated with a single PS tail molecular weight of 1.4 kDa.Specifically,the para-and meta-isomers show hexagonally packed cylinders phases with slightly different order-disorder transition temperatures(~120℃ and~130℃)and the ortho-isomer exhibits an order-order transition from a kinetically favored,metastable dodecagonal quasi-crystal phase to a thermodynamically stable sigma phase at~120℃,as well as a further transition into the disordered state at~140℃.The phase diagram was constructed and their differences were rationalized based on the calculated interfacial area per molecule.This work demonstrates that tiny structural disparity could not only lead to unconventional phase formation in single-component macro-molecules,but also render dynamic and rich phase behaviors in these macromolecular assemblies.