Determination of the critical micellar temperature of F127 aqueous solutions at the presence of sodium bromide by cyclic voltammetry

The properties of Pluronic F127 aqueous solutions with the variation of concentration and temperature were studied by cyclic voltammetry at the presence of sodium bromide. By this method, the relationship between the peak currents of electroactive probe, 2, 2, 6, 6-tetramethyl-1-piperidinyloxy (TEMPO), and the viscosity of F127 aqueous solutions within some temperature ranges was discussed, and the diffusion coefficient (D) of TEMPO in F127 aqueous solutions at various concentrations under different temperatures was determined. The critical micellar temperature (CMT) of F127 aqueous solution at various concentrations can be obtained from the curve of the peak current i _p against the square root of reciprocal viscosity (1/η)^1/2 and from the curve of logarithm diffusion coefficient (logD) of TEMPO as a function of reciprocal temperature (1/T). All the results are in good agreement with the results from ¹H NMR measurements. Besides, the thermodynamic parameters such as diffusion activation energy (E _D) and hydrodynamic radius (R _H) can be also obtained from the above two curves. A new method was introduced to determine the CMT of copolymer systems, which is simple, quick, and accurate.