Effect of ionic liquid on diffusion in P123 gel: fluorescence correlation spectroscopy

Abstract

The effect of two room-temperature ionic liquids (RTILs) on the diffusion of three fluorescent dyes in the gel phase of a triblock copolymer, (PEO)₂₀-(PPO)₇₀-(PEO)₂₀ [Pluronic P123; poly ethylene oxide (PEO), poly propylene oxide (PPO)], was studied by using fluorescence correlation spectroscopy (FCS). We used three dyes, 4-(dicyanomethylene)-2-methyl-6-(4-dimethylaminostyryl)-4H-pyran (DCM), coumarin 480 (C480), and coumarin 343 (C343). By field-emission scanning electron microscopy (FESEM), it was observed that the macroscopic structure of the P123 gel remained unaffected upon addition of RTIL. In the absence of RTIL, the diffusion coefficient (D_t) of the hydrophobic dye DCM (1 μm²s^-1 at the core) is smaller than that of the other two hydrophilic dyes (7μm²s^-1 for C480 and C343). On addition of RTIL, the D_t values of all of the dyes increase, indicating a decrease in local viscosity (η_eff). The η_eff of the core of the RTIL-P123 gel estimated from the D_t of DCM is lower than that of both the P123 gel (at the core η =90 cP) and RTIL (η =110 cP). It is shown that the RTIL affects the structure of the gel by modifying the size of the micellar aggregates and by penetrating the core.