Surface Adsorption in a Surfactant/Clay Mineral Solution

Abstract

The complexes formed in aqueous mixture suspensions of the synthetic clay mineral Laponite and cetyltrimethylammonium bromide (CTAB) have been investigated by small-angle neutron scattering (SANS). All suspensions were prepared with a constant initial concentration of Laponite, but the amount of CTAB was varied. The SANS intensity patterns verify that suspended Laponite in dilute suspension is in the form of disks of diameter ∼30nm and thickness ∼1 nm. SANS indicates that this disk morphology, with the same diameter but with a thickness of about 4 nm, is retained for the suspended complexes, even if the CTAB in the aqueous medium is in considerable excess. SANS and chemical analysis show that a complex must adsorb CTAB to an amount corresponding to at least two multiples of the clay's cation exchange capacity to be dispersed. The amount of CTAB adsorbed as a function of CTAB in the precursor solution is discussed. We also report the effect the presence of clay on CTAB micelle formation as a function of CTAB concentration.