FLUORESCENCE STUDIES OF SOLUTE MICROENVIRONMENT IN COMPOSITE CLAY SURFACTANT FILMS

Microenvironnental polarity and viscosity in ordered composite films made from dialkyldimethylammonium surfactants and clay were studied by using the fluorescent probes pyrene and 1,3-di(1-pyrenyl)propane (DPP). A decrease in monomer fluorescence and an increase in excimer peaks as temperature increases through the phase transition region allowed estimation of phase transition temperatures (T-c). The viscosity and polarity of probe microenvironments decreased with time of soaking the films in water, although X-ray diffraction indicated no changes in interlayer spacing. After 5 days of soaking, viscosities and polarities achieved values similar to those in the methylene chain regions of phospholipid vesicles. Results suggest that probes in freshly prepared films reside close to surfactant head groups but move toward the interior of surfactant bilayers when soaked in water for long periods. Viscosities found in these well-soaked films may be characteristic of microenvironments of nonpolar reactants when composite films are used for catalysis.