SIZE OF SPHERICAL MICELLES OF DODECYLPYRIDINIUM BROMIDE IN AQUEOUS NABR SOLUTIONS

Static light scattering from aqueous NaBr solutions of dedecylpyridinium bromide (DPB) has been measured over the range of NaBr concentrations from 0 to 6.00 M. The reduced scattering intensity does not show any angular dependence. At a given NaBr concentration, the reduced intensity increases with increasing micelle concentration. At a given DPB concentration, it is higher at higher NaBr concentrations if the NaBr concentration is lower than 0.50 M, but it decreases when the NaBr concentration increases further. The Debye plots give micelle molecular weights from 15 100 in water to 23 200 in 0.30-6.00 M NaBr, corresponding to micelle aggregation numbers from 46.0 to 70.7, respectively. Spherical micelles are stable over the whole range of NaBr concentrations. The micelle size increases with increasing NaBr concentration from 0 to 0.30 M, but it remains unaltered from 0.30 to 6.00 M NaBr. The linear double logarithmic plot between molecular weight and ionic strength consists of two parts, crossing at 0.30 M NaBr. The micelle charge is estimated as 26.7 from the slope of the line between 0 and 0.30 M. The degree of ionization is high and is 0.580 in water and 0.378 above 0.30 M NaBr. From 0 to 3.00 M NaBr the second virial coefficient is positive, but beyond 3.00 M it is slightly negative.