Influence of the chemical structure of dyes and surfactants on their interactions in binary and ternary mixture

Abstract

The influence of the structures of both dye and surfactant on the strength of the intermolecular forces operating between dye anions and surfactant cations in the presence of nonionic surfactants has been studied using potentiometry. Two anionic azo dyes, C.I. Acid Orange 7 (AO7) and C.I. Acid Red 88 (AR88), two cationic surfactants, n-dodecyltrimethylammonium bromide (DTA) and n-hexadecyltrimethylammonium bromide (CTA) and two nonionic surfactants, 4-(1,1,3,3-tetramethylbutyl)phenyl polyoxyethylene(10)-ol, Triton X-100 (TX100), and polyoxyethylene(23)lauryl ether, Brij 35 (BR35), were used. From potentiometric measurements, the equilibrium constants, K 1 and κ 1, and the standard free energy change, Δ G 1 o , for the first association step of dye–surfactant and surfactant–surfactant complex formation in binary and ternary mixtures were calculated. The results show that the strength of dye–surfactant interactions, as well as the stability of the complex formed, increases with increasing hydrophobicity of surfactant and dye. The influence of the hydrophobicity of the anionic dye and cationic surfactant on their interactions is decreased in the solution of nonionic surfactant. At the same time, the presence of structural elements of the nonionic surfactants, which promotes an increase in the attractive forces between the cationic and nonionic surfactants, decreases the strength of the interactions between the cationic surfactant and the anionic dye.