Forces between bilayers of cetyltrimethylammonium bromide in micellar solutions

A direct force-measuring technique has been used to study the interaction forces between adsorbed CTAB (cetyltrimethylammonium bromide) bilayers at concentrations well above the CMC (critical micelle concentration). An analysis of these results based on the Poisson-Boltzmann equations leads to the conclusion that CTAB micelles and adsorbed bilayers are about 22(±4)% dissociated. The apparent agreement of bilayer and micellar ion binding parameters raises an important challenge for theories of double-layer interactions. In addition, the double-layer decay lengths observed in these micellar solutions appear to be due entirely to the dissociated bromide and free CTA+ ions, with no apparent contribution from charged micelles.