Aggregation behavior of pluronic triblock copolymer in 1-butyl-3-methylimidazolium type ionic liquids

Three amphiphilic poly(oxyethylene)-poly(oxypropylene)-poly(oxyethylene) ethers triblock copolymers, denoted Pluronic L61 (PEO3PPO30PEO3), Pluronic L64 (PEO13PPO30PEO13), and Pluronic F68 (PEO79PPO30PEO79) were shown to aggregate and form micelles in ionic liquids (ILs) 1-butyl-3-methylimidazolium tetrafluoroborate (bmimBF4) and 1-butyl-3-methylimidazolium hexafluorophosphate (bmimPF6). The surface tension measurements revealed that the dissolution of the copolymers in ILs depressed the surface tension in a manner analogous to aqueous solutions. The cmcs of three triblock copolymers increase following the order of L61, L64, F68, suggesting that micellar formation was driven by solvatophobic effect. cmc and gamma cmc decrease with increasing temperature because hydrogen bonds between ILs and hydrophilic group of copolymers decrease and accordingly enhance the solvatophobic interaction. Micellar droplets of irregular shape with average size of 50 nm were observed. The thermodynamic parameters DeltaGm0, DeltaHm0, DeltaSm0 of the micellization of block copolymers in bmimBF4 and bmimPF6 were also calculated. It was revealed that the micellization is a process of entropy driving, which was further confirmed by isothermal titration calorimetry (ITC) measurements.