Effects of metal ions on the micellization of ionic Surfactants

The effect of metal ions (Cu(II), Zn(II), Co(II), Ni(II), La(III), Fe(III)) on the critical micelle concentration (CMC) of ionic surfactants (sodium dodecyl sulfate (SDS) and hexadecyltrimethylammonium bromide (CTAB)) were investigated at 25 +/- 0.1degreesC, mu = 0.1 M (KNO3), using conductivity method in this paper A series of general empirical expressions about the relationship between the CMC values for SDS and CTAB and the concentrations of metal ions have been derived. The results showed that the CMC values for both SDS and CTAB decreased with increasing the concentrations of metal ions. This can be intetpreted by the counterion effect and the entropy driving effect.