The Hydrophobic Effect on the Adsorption of Rhodamines in Aqueous Suspensions of Smectites. The Rhodamine 3B/Laponite B System

Electronic absorption and fluorescence spectroscopies are applied to study the adsorption of rhodamine 3B dye on Laponite particles in aqueous suspensions. The adsorption on the clay favors the aggregation of the dye. The monomer and aggregates of rhodamine 3B can be adsorbed on both the external and the internal surfaces of Laponite, and their presence depends on the loading of the dye on the clay and the aging of the samples. The aggregation in the interlamellar space leads to the dimer and the trimer (or higher aggregates) of rhodamine 3B with a head-to-tail geometry. The comparison of the present results with those previously reported for the rhodamine 6G/Laponite system demonstrates the effect of the hydrophobicity on the adsorption of dyes in Laponite which affect not only the tendency of the dye to self-associate but also the geometric structure of the aggregates.