Studies on anionic dye Eosin Y in mixed anionic micellar medium

Abstract

Dye-Surfactant interactions in aqueous solution are important in industrial processes. Generally, dyes associate strongly with oppositely charged surfactants. But, similarly charged dye-surfactants are not preferred anticipating repulsion. To gain insight into the nature and extent of interaction between anionic dye Eosin Yellow (EY) and mixed anionic micellar system, this study was undertaken. Mixed micellar system comprised of anionic, Sodium dodecyl sulfate (SDS) and nonionic Pluronic L-35 (L-35). The characterizations employed were FTIR Spectroscopy, Conductivity, UV visible spectroscopy, Fluorescence spectroscopy and SEM studies. A red shift with enhancement of intensity was observed both in UV-absorption and emission spectra of EY when interacted with SDS + L-35 mixed micellar system. From the conductance measurements, the counter ion binding constant β was calculated. Subsequently, various thermodynamic parameters viz., ΔGm, ΔHm and ΔSm were evaluated using β. The Gibbs free energy of micellization, ΔGm was observed to be −4.56 kJ mol−1, −13.34 kJ mol−1 and −18.55 kJ mol−1 for SDS, SDS + L-35 and SDS + L-35 + EY respectively. The negative values of ΔGm are indicating the spontaneous binding occurring between EY and SDS + L-35. The SEM images revealed enlargement of grain size of the mixed micelle after encapsulation of EY. To the best of our knowledge this is the first report of anionic dye EY with an anionic mixed micellar system.