The Micellar Properties of α,ω-Alkanediammonium Bis(dodecyl sulfate) in Aqueous Solutions

The micellar properties of α,ω-alkanediammonium bis(dodecyl sulfate) with hydrocarbon chain length (n) from 3 to 6 were studied by conductivity, surfactant ion activity, and fluorescence quenching measurements. The critical micelle concentration (CMC) decreases gradually with increasing n in such a way that ln CMC vs. n plot gives a straight line above n = 3. The binding degree of counterion head group to the micelle remains virtually constant of 0.95 regardless of n studied. The estimated value of −0.36 kT for the transfer free energy per methylene group of counterion from aqueous to micellar environments suggests that the hydrocarbon part of the counterion participates in the weak hydrophobic interaction with micellar core. Although the micelle aggregation number is always larger than those of bivalent metal dodecyl sulfates, it tends to decrease as n increases.