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 s tudy the adsorption of rhodamine 3B dye on Laponite particles in aqueo us suspensions. The adsorption on the clay favors the aggregation of t he dye. The monomer and aggregates of rhodamine 3B can be adsorbed on both the external and the internal surfaces of Laponite, and their pre sence depends on the loading of the dye on the clay and the aging of t he samples. The aggregation in the interlamellar space leads to the di mer and the trimer (or higher aggregates) of rhodamine 3B with a head- to-tail geometry. The comparison of the present results with those pre viously reported for the rhodamine 6G/Laponite system demonstrates the effect of the hydrophobicity on the adsorption of dyes in Laponite wh ich affect not only the tendency of the dye to self-associate but also the geometric structure of the aggregates.