Spectroscopic studies of interactions between C.I. Reactive Orange 16 with alkyltrimethylammonium bromide surfactants.

In the present study, the influence of surfactants on spectral properties of an azo dye in aqueous solutions has been investigated by means of UV-vis spectroscopy in submicellar and micellar concentration range. The spectral signature of the polarity of the azo dye C.I. Reactive Orange 16 (RO16) exhibits sensitivity to the polarity of the dye's environment. This dependence of absorption on microenvironment was used to investigate the ion pair complex formed from electrostatic interaction of a series of alkyltrimethylammonium bromide surfactants (CmTAB, m=12, 14, 16 and 18) with the anionic azo dye RO16. It was observed that the aggregation of surfactant and dye takes place at surfactant concentration far below the critical micelle concentration of the individual surfactant. Aggregation is reflected by the appearance of a new absorption band in the spectrum of the dye. Spectral behavior of dye-surfactant solution with varying concentration of surfactant confirms that electrostatic interaction between dye and surfactant occurs up to a certain level. Beyond this concentration, with addition of surfactant, micelles occur and all dye molecules are accommodated into a normal micelle as monomeric molecules. The short-range hydro phobic interactions are very important factors as the long-range electrostatic forces on the dye-surfactant aggregation in aqueous solution. The effect of the length of the alkyl chain of the surfactant on the complex formation between cationic surfactant and reactive dye was that the hydrophobicity of alkyl chains plays an important role in complex formation. Going from less hydrophobic solution to the more hydrophobic micellar environment, the occurrence of complex is found at lower surfactant concentration. Because the CMC values of dye-surfactant solution are decreased with increasing alkyl chain length.