Thermodynamics and Mechanism of the Block Copolymer Micelle Shuttle between Water and an Ionic Liquid

The micelle shuttle, whereby amphiphilic poly((1,2-butadiene)-b- ethylene oxide) (PB-PEO) block copolymer micelles reversibly transfer between water and a hydrophobic ionic liquid upon a temperature stimulus, is of interest in delivery, reaction and separations in synthesis and biphasic catalysis involving ionic liquids. A solvophobic dye-labeled short PB homopolymer is loaded into the PB-PEO micelles and quantitatively shuttled between the two fluids. The micelle distribution in the biphasic system has a favorably strong temperature dependence as revealed by quantitative fluorescence analysis, which is further used to extract the standard Gibbs free energy change ($\Delta$G$^{\circ}$), enthalpy change ($\Delta$H$^{\circ}$) and entropy change ($\Delta$S$^{\circ}$) of the transfer. The slow yet spontaneous micelle shuttle is explored under quiescent conditions to understand the transfer kinetics. A detailed mechanism for the transfer is proposed.