SPECTROSCOPIC DETERMINATION OF REFRACTIVE-INDEX AND DIELECTRIC-CONSTANT AT INTERFACES, USING PHOTOPHYSICAL PROBE MOLECULES

In this study a UV-vis spectroscopic technique is presented for the determination of the refractive index and dielectric constant in restricted regions. Both the classical Bayliss model and a modified Bekarek model were employed to calculate the refractive index and dielectric constant of the media (e.g. polymer, silica gel, and zeolite). The studies show that the refractive index (n) of these media are approximately 1.58 (polystyrene), approximately 1.33 (silica gel), and approximately 1.45 (zeolite X), which are identical to the values reported in the literature. Increasing pretreatment temperature of silica gel is shown to decrease the refractive index, which indicates that the probe molecule is exposed to a less polar or dehydrated environment. The refractive index in a zeolite is shown to increase in the presence of coadsorbed water. On colloidal clay surfaces, increasing the concentration of a long chain alkylpyridinium surfactant around the adsorbed probe molecule is shown to decrease the refractive index in agreement with the picture that the environment of the probe becomes more hydrophobic as an aliphatic surfactant layer builds up on the surface. The data agree with earlier luminescence probing studies in this system. The studies presented amplify and extend earlier luminescence probing studies in heterogenous media, and present a method of measuring additional physical parameters to describe complex systems.