Photoacoustic study of Rh B dye on silica particles : Electronic spectra and determination for depth of distribution limit.

Abstract

The photoacoustic spectra (PA spectra) of Rhodamine B dye adsorbed on silica particles (Rh B/ SiO2) have been measured in the wavelength region of 300-700nm. The spectral shape resembles the absorption spectrum of Rh B aqueous dilute solution although less than 9nm shifts of maxima to the high energy side are observed in the PA spectra. This similarity suggests that Rh B molecules on silica particles are as highly dispersed as those in the solution. The reasons for a slight difference in band shape are considered between the PA spectrum and the diffuse reflection spectrum of Rh B/ SiO2. When the modulation frequency of light for excitation is increased some unknown species being adsorbed very near to the surface of silica particles are detected in the PA spectra in the wavelength region of 600-700nm. The ratio of the PA signal height at the maximum of Rh B (λ=545nm) to that at the surfactant's band above (λ=700nm) is plotted vs. the thermal diffusion length. This analysis indicates that Rh B dye molecules are distributed within the depth of 64μm from the surface of silica particles.