Direct measurement of depletion and structural forces in a micellar system

Abstract

The force as a function of separation is measured between two mica surfaces coated with adsorbed bilayers of cetyltrimethylammonium bromide (CTAB) and immersed in aqueous ionic micellar solutions of CTAB. At low separations double-layer forces are observed and arise soley from the dissociated counterions and free ${\mathrm{CTA}}^{+}$. At large separations, the repulsion is reduced and a secondary minimum in the interaction potential deepens when the micellar concentration is increased. Finally, at higher concentrations, structural effects superimpose an oscillatory force profile at further separations.