Pluronic based neutral-ionic binary micellar surfactant systems for solubilizing the cationic methylene blue dye

Abstract

The interaction of cationic methylene blue (MB) dye with binary micellar systems of non-ionic Pluronic®L-81 containing anionic sodium dodecyl sulfate (SDS) or cationic cetyl trimethyl ammonium bromide (CTAB) surfactants were probed through conductivity, uv-visible, FTIR, DLS, and zeta potential measurements with an objective to identify better solubilizing system at room temperature. The CMC of both SDS and CTAB was lowered in MB+L-81+SDS or CTAB systems. The absorption spectrum of MB showed a slight blue-shift with enhanced intensity upon increasing the concentration of anionic SDS and cationic CTAB, reflecting the strong electrostatic interaction and formation of micelles due to the solubilization of MB by L-81+SDS/CTAB systems. The higher negative value of ΔGm for L-81+SDS (-24.18 kJ/mol) than L-81+CTAB, (-17.07 kJ/mol) indicated better stability of MB in SDS system than CTAB. This could be attributed to the electrostatic attraction between dissimilarly charged MB (cationic) and SDS (anionic) in the ternary (MB+L-81+SDS) system and repulsive steric interaction between positively charged MB and CTAB. This was confirmed from micellar size analysis using dynamic light scattering (DLS) measurements and binding constant values. The estimated CMC values were comparable with the literature data. Hence, based on these results we propose that L-81+SDS binary system can be applied as a potential medium for removal of MB from the industrial effluents.