Phase Behavior of Double Zwitterionic Block Copolymers in Water: Morphology Transition through Concentration Dependent Selectivity of Water Partitioning |
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Authors: | Yuji Higaki Masaya Takahashi Takumi Masuda |
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Institution: | 1. Department of Integrated Science and Technology, Faculty of Science and Technology, Oita University, 700 Dannoharu, Oita, 870-1192 Japan;2. Graduate School of Engineering, Oita University, 700 Dannoharu, Oita, 870-1192 Japan |
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Abstract: | Phase behavior of double zwitterionic diblock copolymers composed of a poly(carboxybetaine methacrylate) (PCB2) and a poly(sulfobetaine methacrylate) (PSB4) (PCB2n-b-PSB4m) has been mapped out in aqueous solutions. Phase diagrams are constructed with polymer concentration, ϕ, ranging from 0.08 to 0.80 and PSB4 volume fraction in the PCB2n-b-PSB4ms, fPSB4, ranging from 0.23 to 0.93 at 25 °C. PCB2n-b-PSB4m aqueous solutions show symmetric phase diagram above ϕ = 0.55, indicating that water is nearly neutral with respect to PCB2 and PSB4. The morphology transforms from columnar with PCB2 cylinders to lamellar to columnar with PSB4 cylinders with decreasing ϕ, and the phase boundaries exhibit a negative slope below ϕ = 0.45. The morphology transition is rationalized in terms of interfacial curvature modulation through the volume expansion of the PCB2 phase due to the selective water partitioning. The lyotropic mesophase of double hydrophilic block copolymers is a unique molecular compartment for hydrophilic molecules with low interfacial tension. |
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Keywords: | block copolymers microphase separation small-angle x-ray scattering water zwitterionic polymers |
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