Dye–Surfactant Interaction in Submicellar Concentration Range

Interactions of cationic dyes, viz., phenosafranine (PSF), safranine O (SFO) and safranine T (SFT) with anionic surfactants, viz., sodium dodecyl sulfate (SDS) and sodium octyl sulfate (SOS) in submicellar concentration ranges have been investigated spectroscopically. The interaction has been shown to be an induced protonation of the dye in the dye–surfactant ion pair. Even though the opposite charges on the dye and the surfactant are the primary requirements for the ion pair formation, it is the hydrophobicity of the surfactant as well as of the dye which induces the protonation. The spectroscopic and thermodynamic parameters show that the orders of effectiveness of the dyes and the surfactants for the interaction are, SFO > SFT > PSF and SDS >> SOS.