Solubilization of direct dyes in single and mixed surfactant system: A comparative study

Interaction of direct dyes (Direct Orange 26 and Direct Red 9) has been investigated via spectroscopic analysis in single cationic (cetyltrimethylammonium bromide) and cationic-nonionic mixed surfactant media. The solubilization capabilities of surfactants solutions have been assessed in terms of the partition coefficient (K_x) and binding constant (K_b). Critical micelle concentration (CMC) of the surfactant, electrostatic interactions, hydrophobic associations, and polarity of the medium plays important role in the said process. Significant enhancement in the solubility of both dyes was observed on the addition of non-ionic surfactants (Triton X-100 and Tween-20) in the CTAB solution. Solubility was found to be directly related to the extent of mixed micellization. The negative values of the Gibbs energy of binding (ΔG_b) and Gibbs energy of partition (ΔG_p) are the predictors to prove the feasibility and spontaneity of the process. The results, herein, suggest that the use of mixed micellar media for solubilization of direct dyes is advantageous over that of a single surfactant.