Ternary Block Copolymer - Water - "Oil" Systems: Effects of "Oil" Type and Block Size on Phase Behaviour and Structure

Sammanfattning: It has recently been established in our group that amphiphilic block copolymers consisting of a hydrophilic and a hydrophobic part can self-assemble in the presence of selective solvents (“water” and “oil”) into a variety of different solution and lyotropic liquid crystalline microstructures. The effects of the “oil” type, hydrophilic block size and hydrophobic block type on the phase behavior and microstructure of ternary isothermal copolymer - oil - water systems have been addressed in this thesis. A poloxamer poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) triblock copolymer (Pluronic F127: E100P70E100), was investigated in the presence of water and three different “oils” of varying polarity, p-xylene, n-butyl acetate and butan-1-ol. The number and types of phases, as well as the composition range of their stability, were different for each ternary system. The location of the “oils” in the different self-assembled microstructures has been deduced from the characteristic length-scales obtained from small angle X-ray scattering (SAXS) experiments and the constraints imposed by the copolymer total volume fraction and interfacial area: all xylene was found to be present in the core of the oil-in-water microdomains, butanol to be located at the interfacial region between P and E, while butyl acetate to contribute to both the core and the interfacial domains. The influence of the interfacially active butanol on the phase behavior is evident in the formation of extended L2 water-lean solution regions and in the stability of lamellar regions at relatively low copolymer contents. The self-assembly of another poloxamer (Pluronic P123: E20P70E20) in water and butyl acetate or butanol was studied in order to compare with that of E100P70E100. E100P70E100 andE20P70E20 have the same block architecture and P block size, but different E block sizes. The high E (hydrophilic) content of E100P70E100 favors “normal” (oil-in-water) structures: the copolymer-water axis is dominated by structures with spherical interfacial curvature; the presence of significant amounts of oil is required for cylindrical and lamellar structures to form. Both normal and “reverse” (water-in-oil) structures are thermodynamically stable in the E20P70E20 - butyl acetate - water system. The self-assembly properties of newly-synthesized copolymers having the same architecture and molecular weight as the poloxamers but a different hydrophobic block type, poly(n-butylene oxide)= poly(tetrahydrofurane): T, has also been examined. E100T27E100 formed micelles at a lower concentration than E100P70E100; the “molecular” weight of the E100T27E100 micelles did not change with temperature, but their z-weighted radius of gyration did. In a ternary system with butanol and water, E100T27E100 formed just a single one-phase solution region which extended from the water-rich corner to the butanol-rich corner.