Effect of biologically active amino acids on the surface activity and micellar properties of industrially important ionic surfactants

The surface tension and fluorescence measurements have been carried out to study the interactions present between anionic surfactant, sodium dodecyl benzene sulfonate (SDBS) and cationic surfactant, dodecyltrimethylammonium bromide (DTAB), in aqueous solution, in presence and absence of additives (glutamine, histidine and methionine) at different composition and temperature. Critical micelle concentrations (CMCs) have been determined using surface tension measurement. In case of SDBS, the CMC value increases with rise in temperature while in case of DTAB, it shows a U-type behavior, meaning thereby, both hydrophobic and hydrophilic dehydration becomes prominent in case of DTAB while only hydrophilic dehydration plays decisive role for the micellization to take place in case of SDBS. From surface tension data, the surface excess concentration at air/water interface (Γmax), minimum area per surfactant molecule (Amin) and the surface pressure at CMC (πCMC) have been evaluated. Thermodynamic parameters of transfer, adsorption and micellization have also been evaluated and discussed in detail. Fluorescence probe study has been carried out to outline the results stated above. The CMC values calculated using pyrene as a fluorescent probe at room temperature resembles well with the micellar values determined using surface tension measurement.