Conductometric, tensiometric and spectroscopic studies on the interaction of congo red with dodecyltrimethylammonium bromide: Effects of electrolyte and non-electrolyte

To investigate the interactions between congo red (CR) dye and dodecyltrimethylammonium bromide (DTAB) surfactant in aqueous, electrolytic (MgCl2) and non-electrolytic (urea) solutions, conductometric, tensiometric and spectroscopic methods were used. Conductivity and surface tension measurements were performed to evaluate the critical micelle concentration (cmc) values of the cationic surfactant, DTAB. The change in Gibb's energy (Delta G0m), enthalpy (Delta H0m), and entropy (Delta S0m) of micellization were also calculated. The cmc value of DTAB was found to drop in the presence of CR dye and a further decrease was noticed in the presence of MgCl2, while the values augmented when urea was present. Due to the interruption of the structured water molecules encasing the hydrophobic groups of the DTAB, the cmc values augmented with an increase in temperature. The presence of MgCl2 led to a greater degree of ionization (alpha) of DTAB micelles. For all of the systems under study, the values of Delta G0mand Delta H0m were found to be negative. The -T Delta S0m values, which were noted to be higher than Delta H0m values suggest that the gain in entropy possibly be the prime factor that governs the process of micellization. Many of the CR dye molecules were drawn into DTAB micelles as their concentrations in the system were amplified, as evidenced by the absorbance values in UV-Vis spectroscopic studies.