Block copolymer structuring in ionic liquids
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Ionic liquid and block copolymer interactions as reflected in the structural characteristics of self-assembled microstructures are yet to be systematically investigated. Fundamental knowledge is required so as to specifically select the right combinations of block copolymers and ionic solvents with respect to their inherent properties and intrinsic structural characteristics and design/compose materials with desired/anticipated properties for large scale applications. Ionic liquids are new highly ordered salts possessing a molecular cation and an inorganic ion. They support the microstructure formation of surfactants and block copolymers via specific molecular interactions that are poorly understood. Block copolymers are composed of a linear arrangement of moieties of different homopolymers and their phase behavior is of considerable interest for pharmaceutical, medical, cosmetic and other type of industries. We investigate the molecular interactions between PEO/PPO block copolymers and ionic liquids as they are reflected in the structural characteristics of the formed PEO/PPO microstructures. We employ ionic liquids of different structural characteristics. Ionic liquids with structure that resembles the one of water as well as ionic liquids with asymmetric cations but with substantial degree of order enable the ordering of block copolymers. We generated the binary phase diagrams of PEO based block copolymer in ionic solvents and we discuss the microstructural characteristics of the different phases. We combine ionic solvents with molecular solvents i.e. water so as to explore their synergistic effects as self-supporting media. Rich structural polymorphism is afforded by the PEO based block copolymer and the phase regions of the three component phase diagrams are discerned. Lastly, the effect of ionic liquids, on the ternary hexagonal crystals is examined microscopically and their location in the microstructure is assigned.