Adsorption Of Rhodamine 6G Research Articles

Characterization of Polystyrene Latex Surfaces by the Adsorption of Rhodamine 6G

The adsorption of the fluorescent dye rhodamine 6G (R6G) onto polystyrene (PS) latex was investigated as a potential tool for characterizing the surface of PS latex, in particular the density of negative surface charges and their distribution on the surface. The method exploited previous observations that R6G forms nonfluorescent dimers in concentrated solutions and that when R6G is adsorbed to surfaces, R6G dimerization is enhanced. This work examined the influence of ionic strength and particle concentration for variations in R6G adsorption. R6G adsorption was found to be charge-driven in the most dilute regime, and hydrophobically driven in the concentrated regime, with the crossover occurring near the neutralization of negative surface charge by the positive R6G. For negatively charged particles, adsorbed dyes were nearly completely quenched on the surface near the point of charge neutralization, where the dispersions were also unstable. At higher R6G surface loadings, the surface fluorescence was recovered and the dispersions restabilized. No surface quenching could be resolved on cationic latex due to weaker dye adsorption.

Characterization of Rhodamine 6G Adsorbed onto Hectorite by Electronic Spectroscopy

The adsorption of rhodamine 6G onto hectorite is investigated by UV-Vis absorption and fluorescence spectroscopies. The monomer of rhodamine 6G is reported to be adsorbed onto both the external and the internal surfaces, the external adsorption being predominant immediately after the sample preparation. The metachromatic effect observed in the adsorption spectra is attributed to dye aggregation at both the internal and the external surfaces. The experimental results also suggest a tendency of the monomeric form of rhodamine 6G to be adsorbed onto the internal surface after increasing the stirring time, mainly at high clay concentrations in the aqueous suspensions.

Adsorption of Rhodamine 6G onto Polystyrene Latex Particles with Sulfate Groups at the Surface

The adsorption behavior of a fluorescent dye, rhodamine 6G (R6G), onto three anionic polystyrene latex samples of different charge densities has been investigated as a function of the pH and the ionic strength of the aqueous medium. The data fit well to a simple Langmuir binding isotherm, but not to a cooperative binding model. The results show that at low dye concentration adsorption depends mostly on electrostatic interactions, whereas at high concentration hydrophobic interactions prevail.

Spectroscopic Study of the Adsorption of Rhodamine 6G on Laponite B for Low Loadings

AbstractThe adsorption of Rhodamine 6G in aqueous suspension on Laponite B was investigated by electronic absorption and emission spectroscopies. Fluorescence spectra suggest that the monomer is adsorbed at two different surfaces, the external and the internal. A monomer is intercalated in the interlamellar space at low loading of dye (<3% CEC), whereas the monomeric state of the dye seems to be at the solid-aqueous interface in suspensions with high loading (>12% CEC). The metachromatic effect observed in the absorption spectra, for the loading interval between 1% and 15% CEC of Laponite B, is attributed to the dimerization of the dye, which seems, from X-ray diffraction measurements, to be formed at the clay interlayer. The formation constant and the absorption spectrum of the aggregate were obtained and the dimer was structurally characterized by applying the Exciton Theory. The observed fluorescence quenching for loadings lower than 15% CEC is attributed to energy transfer from monomer to the dimer, which obeys the Perrin model.

On the Monomeric and Dimeric States of Rhodamine 6G Adsorbed on Laponite B Surfaces

The adsorption of rhodamine 6G on laponite B is investigated by electronic absorption and emission spectra for loadings higher than 15% of laponite cation exchange capacity (CEC). The experimental results suggest the formation of an externally adsorbed dimer. The spectroscopic and structural characteristics of this aggregate are compared to those of the interlamellar adsorbed dimer previously reported for loadings lower than 15% CEC. A model is proposed to explain the existence of the different adsorbed species, whose relative importance depends on the relative dye/clay concentration.