The Micellar Parameters of [alpha],[omega]-Alkanediammonium Bis(decyl sulfate) Solutions and Their Mixtures

Conductometric and fluorescence probe investigations were carried in order to elucidate the micellar parameters of α,ω-alkanediammonium bis(decyl sulfate) with carbon-chain lengths (n) from 4 to 8 and their mixtures. In single surfactant systems, an increase in n was accompanied by a regular decrease in the critical micelle concentration (cmc) and a rapid increase in the micelle aggregation number (m), while the binding degree of the counter ion head group remained virtually constant at 0.90. The transfer free energy per methylene group of the counter ion from aqueous to micellar environments varied with increasing n from -0.35 kT to -0.68 kT. This fact suggests that the hydrocarbon chain of the counter ion, even with n = 4, can participate in the weak hydrophobic interaction with the micellar interior. In mixed solutions of n = 4 and 6, and n = 4 and 8, the cmc vs. y (mole fraction of n = 4) curves can be well interpreted in terms of the ideal mixing model. In both systems, the value of m gradually increases with increasing y. The fluorescence probe experiments indicate that the local environment around the solubilized pyrene in the mixed micelle resembles one another, regardless of y.