Study of the adsorption of organic molecules on clay colloids by means of a fluorescent probe

Abstract

The adsorption and distribution of molecules on a clay surface has been investigated by means of fluorescent probes, containing pyrene as chromophore and trimethyl ammonium head group, with varying chain length.

After adsorption, in aqueous media, these molecules form clusters on the surface, resulting in ground state interactions and an efficient excimer formation. The lack of these intermolecular interactions in organic media suggests that hydrophobic interactions are the driving force for this clustering.

Co-adsorbed detergent molecules influence the distribution of the probe molecules, at least when the chain length of the detergent is the same as the total length of the probe. For each probe, a so-called “critical chain length” exists, for the detergents to be able to destroy the probe clusters.

Excimer formation has proved to be a good tool to gain additional information on the adsorption process. It was found that excimer formation on the interlamellar surface is less efficient then excimer formation on the external surface. Also, redistribution and exchange phenomena of the adsorbed probe molecules have been observed by studying excimer emission.