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Keywords:

  • diffusion coefficients;
  • dyes/pigments;
  • fluorescence correlation spectroscopy;
  • gels;
  • ionic liquids

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 (Dt) of the hydrophobic dye DCM (1 μm2 s−1 at the core) is smaller than that of the other two hydrophilic dyes (7 μm2 s−1 for C480 and C343). On addition of RTIL, the Dt values of all of the dyes increase, indicating a decrease in local viscosity (ηeff). The ηeff of the core of the RTIL–P123 gel estimated from the Dt 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.