Abstract:

The silylation of thin-film glass sheets with hexamethyl disilazane results in hydrophobic glass surfaces with water contact angles larger than 90°. The adsorption behavior of Rhodamine 6G (R6G) and methylene blue (MB) molecules on the hydrophobic glass from the individual aqueous solutions were investigated by time-resolved optical waveguide spectroscopy and the experimental data were compared with those obtained using hydrophilic glass. The adsorption and desorption rate constants as well as the adsorption free energy for R6G adsorption on the silylated glass were determined by fitting the experimental data with the Langmuir isotherm model. Glass silylation leads to an increased adsorption rate constant, a decreased desorption rate constant, and an enhanced adsorption free energy as compared to those obtained for R6G adsorption on hydrophilic glass. The comparisons indicate that R6G and MB molecules prefer to adsorb onto hydrophobic glass over hydrophilic glass from aqueous solution. Moreover, it was observed that glass silylation can effectively prevent the aggregation of dye molecules at the water/glass interface.

Key words: Surface adsorption, Silylation treatment, Time-resolved optical waveguide spectroscopy, Dye molecule, Adsorption kinetics