The Salt-Induced Sphere–Rod Transition of Micelles of 1-Tetradecylpyridinium Bromide in Aqueous NaBr Solutions

Static light scattering from aqueous NaBr solutions of 1-tetradecylpyridinium bromide (TPB) has been measured over the range of NaBr concentrations from 0 to 0.50 mol dm−3 at 25 °C, and the micelle molecular weight has been estimated. For 0—0.20 mol dm−3 NaBr, the reduced intensity of scattered light does not show any angular dependence, and the molecular weight of the spherical micelle of TPB slightly increases from 27.6 × 103 to 41.4 × 103 with increasing NaBr concentration. Beyond 0.20 mol dm−3 NaBr, the angular dissymmetry of the reduced scattering intensity and a steep increase in the micelle molecular weight from 41.4 × 103 to 177.8 × 103 are observed. Therefore, TPB has been considered to form rodlike micelles. The linear double logarithmic relationship between molecular weight and ionic strength holds for spherical and rodlike micelles, respectively. From the intersection of these two lines, the threshold NaBr concentration for the sphere-rod trainsition of TPB micelle is estimated to be 0.19 mol dm−3, where the micelle has a molecular weight of 41.3 × 103.