Ultrasonic and Thermodynamic Analysis of Molecular Interaction in Sodium Dodecyl Sulphate-Urea-Water Ternary Mixtures at Various Temperatures

This study investigates the ternary mixture of sodium dodecyl sulphate (SDDS) with urea in water through ultrasonic and thermodynamic analyses at temperatures of 303, 308, 313, 318, and 323 K. Experimental values were used to calculate derived parameters such as ultrasonic velocity (U), density (ρ), and viscosity (η). These parameters enabled the computation of acoustic properties, including adiabatic compressibility (βs) and intermolecular free length (Lf). The findings indicate that urea exhibits hydrophilic (structure-breaking, SB) behavior with weak interactions at lower temperatures (303-308 K) and hydrophobic (structure-making, SM) behavior with stronger interactions at higher temperatures (313-323 K). The study demonstrates that ultrasonic velocimetry is a powerful and precise method for characterizing interactions between surfactants and biomolecules. The temperature coefficients of ultrasonic velocity (∂U/∂T) and adiabatic compressibility (∂βs/∂T) were found to have positive and negative values, respectively, further confirming the temperature-dependent interaction behavior of urea. Additionally, relaxation time analysis revealed that the maximum relaxation time for the binary solution occurs at 312 K and the minimum at 323 K, whereas for the ternary solution, the maximum relaxation time is also at 312 K and the minimum at 320 K. These results have significant implications in fields such as solution chemistry, biochemistry, biosciences, surface science, surfactant chemistry, industrial chemistry, and both physical and chemical sciences.