Influence of Halide Ions and Temperature on the Thermophysical Properties of Aqueous Zwitterionic Surfactant Solution

Abstract: The current study investigates the thermophysical properties, including density, dynamic viscosity, and kinematic viscosity, of a zwitterionic surfactant, namely 3-(N,N–dimethylmyristylammonio)propane sulfonate (DMPS), in aqueous solutions both with and without electrolytes (specifically halide ions), within the temperature range of 293 to 333 K with 5 K gap. For the pure zwitterionic surfactant, a decreasing trend was observed in dynamic viscosity, density, and kinematic viscosity with rising temperature. However, in the presence of halide ions (salt), an increase in their concentration led to rising values of thermophysical properties. Nonetheless, akin to the pure surfactant, a declining trend was noted with rising temperature with electrolytes (halide ions). The efficacy of halide ions followed order: F^– ˂ Cl^– ˂ Br^–. Additionally, the activation energy of the surfactant (DMPS) was assessed both with and without halide ions (electrolytes). Analysis through Fourier-transform infrared spectroscopy (FTIR) and proton nuclear magnetic resonance spectroscopy (¹H NMR) confirmed physical interactions between the surfactant DMPS and halide ions in the solutions. No evidence of chemical reactions or complex formations was observed during this interaction.