STUDY OF THE ADSORPTION LAYER AT THE GLASS-DYE SOLUTION INTERFACE BY VARIABLE INCIDENCE-ANGLE INTERNAL-REFLECTION SPECTROMETRY

The reflectivity was measured at the interface between the glass subst rate and the Brilliant Blue (BB) or Methylene Blue (MB) aqueous soluti on as a function of the angle of incidence at 632.8 nm from a He-Ne la ser. The relationship between the reflectivity and the angle of incide nce was analyzed by an approximate expression derived from the basic t heory of internal reflection spectroscopy. On the other hand, a plot o f the reflectivity against the effective thickness was used as a ready diagnosis of the dye adsorbed by the glass substrate. From the result s it has been suggested that BB is not adsorbed, whereas MB is. Based on a parameter obtained experimentally, the thickness of the adsorptio n layer was determined to be 0.65+/-0.18 nm. This result suggests that the MB cation is adsorbed parallel to the glass surface to form a mon omolecular layer. Further, it has been revealed from a similar analysi s that the addition of a cationic surfactant with a long alkyl chain i n the MB solution prevents the adsorption of MB by the glass substrate , whereas the addition of an anionic surfactant with a long alkyl chai n promotes adsorption.