Interaction Between Anionic Dyes And Cationic Surfactants

The interactions between dyes, Orange II, Alizarin yellow R or Methyl Orange, with nine kinds of cationic surfactants, N-dodecyl-hydroxyl-dimethyl ammonium bromide,N-dodecyl-hydroxyl-dimethyl ammonium bromide , N-tetradecyl-hydroxyl-dimethyl ammonium bromide, N-tetradecyl-dihydroxyl-methyl ammonium bromide , N-cetyl- trimethyl ammonium bromide,N-cetyl-hydroxyethyl-dimethyl ammonium bromide, N-cetyl-dihydroxyethyl-methyl ammonium bromide, N-octadecyl-hydroxyethyl dimethyl ammonium bromide and N-octadecyl- dihydroxyl-methyl ammonium bromide were studied by using UV-Vis spectroscopy and conductivity measurements.UV-Vis absorption spectra and conductivities of various dye-surfactant aqueous solutions were measured. The absorbance of a dye-surfactant solution was obviously lower than that of the corresponding dye aqueous solution without surfactant, and it increases with the increase of the concentration of surfactant. No obvious red shift or blue shift of absorptions in Orange II -surfactant aqueous solutions was found. The shoulder peaks were observed at about 500nm and the shoulders became more obvious with the increase of the carbon chain length of the surfactant. This phenomenon might result from the ion-pairs formed between Orange II and surfactants. There were no obvious shoulders in the UV-Vis spectra of Alizarin-surfactant aqueous solutions, but slightly red shifts were found.The strong interactions between dyes and surfactants were also quantitatively checked and explained with different theoretical models from literature on the basis of the experimental absorbance and conductivity data. The critical micelle concentrations (CMC) of the surfactants at different temperatures were determined by using spectroscopy and conductance methods respectively. The CMC values for a surfactant calculated from the two methods for the three dye-surfactant systems were almost the same, showing that all the three dyes can be used as the indicators of the CMC determination for cationic surfactants.The equilibrium constants and some thermodynamic functions of the interactions between dyes and surfactants were calculated from the experimental absorbance and conductivity data respectively. The interaction constants of dye-surfactant systemschange linearly with temperatures. It was found that the longer hydrophobic chains and more hydroxyethyls the surfactant has and the stronger interaction with dyes it has. As an example, the interaction constant of N-octadecyl-dihydroxyl-methyl ammonium bromide with dye is larger than that of jV-dodecyl-hydroxyl-dimethyl ammonium bromide with dye. However, the interaction constant of A'-cetyltrimethyl ammonium bromide with dye is larger than that of TV-cetyl-hydroxyl-dimethyl ammonium bromide with dye, which can be explained from the steric effects and hydrogen bonding association.From the combination of the electrostatic and hydrophobic interactions and steric effects, it can be concluded that the order from strong to weak interaction between three dyes with the surfactants is 7V-octadecyl-dihydroxyl-methyl ammonium bromide, iV-octadecyl- hydroxyl-dimethyl ammonium bromide, A^-cetyl-dihydroxyl-methyl ammonium bromide, TV-cetyl-trimethyl ammonium bromide, N-cetyl -hydroxyl-dimethyl ammonium bromide,JV-tetradecyl-dihydroxyl-methyl ammonium bromide, jV-dodecyl-dihydroxyl-methyl ammonium bromide, N-tetradecyl-hydroxyl-dimethyl ammonium bromide, and then TV-dodecyl-hydroxyl-dimethyl ammonium bromide.