Spectrophotometric and conductometric studies on the interaction of surfactant with polyelectrolyte in the presence of dye in aqueous medium

Abstract

The concentration of methyl red (MR) dye has a significant influence on how the CTAB + NaPSS complex (CTAPSS) aggregates and sticks together. However, the effect of MR dye on CTAPSS has not yet been thoroughly investigated. The major goal of this work is to use conductometry and UV–Vis. techniques to investigate the influence of MR on the interactions between a cationic surfactant, cetyltrimethylammonium bromide (CTAB) and an anionic polyelectrolyte, sodium polystyrene sulfonate (NaPSS) in aqueous environments. By observing changes in the dye's spectra and the breaking points of conductometric curves, it is obvious that MR causes the development of surfactant aggregates. Critical aggregation concentration (CAC), apparent critical micelle concentration (CMC*), ionization degree (α), binding constant, and various other important thermodynamic parameters were determined by conductivity techniques at 298.15 ± 0.2 K. The CAC and CMC* values dropped on raising the concentration of CTAB with MR in the CTAB + NaPSS + MR system, which is caused by the substantial electrostatic interactions between CTAB/NaPSS and MR. With anionic MR, aggregation and micellization become easier, as seen by hypsochromic shift and reduction in the absorption band's intensity. With increasing CTAB concentrations, the absorption spectra of MR were observed between 430 and 440 nm for the basic form steadily dropped to 414–421 nm. The Benesi-Hildebrand equation was used to calculate the binding constants from the absorption spectra of MR. The CMC of CTAB in water was determined to be 0.00091 molL-1 but the CMC* of CTAB for the CTAB + NaPSS system was determined to be 0.001438 molL-1 and CMC* for the CTAB + NaPSS + MR system was observed to be 0.001328 molL-1 by conductivity and 0.001310 molL-1 by UV–Vis. spectroscopy at 298.15 ± 0.2 K. Also, it is observed that CMC* obtained by spectroscopy is slightly lower (0.001310 mol L-1) than those obtained from conductometry (0.001328 mol L-1) since the spectrum is extremely sensitive for molecular interactions and their properties.