Viscosity, speed of sound (u), and density (ρ) have been measured in aqueous glycyl glycine solution over a temperature range from 293.15 to 313.15 K with a 5 K interlude to evaluate the volumetric and compressibility properties of bio-surfactants, namely sodium cholate (NaC; 1-20 mmol∙kg-1) and sodium deoxycholate (NaDC; 1-10 mmol∙kg-1). Density and viscosity findings provide information on both solute-solute and solute-solvent types of interactions. Many other metrics, such as apparent molar adiabatic compression (κS,φ), isentropic compressibility (κS), and apparent molar volume (Vφ), have been calculated from speed of sound and density measurements, utilising experimental data. The results show that the zwitterionic end group in the glycyl glycine strongly interacts with NaDC and NaC, promoting its micellization. Since the addition of glycyl glycine causes the bio-surfactant molecules to lose their hydrophobic hydration, the observed concentration-dependent changes in apparent molar volume and apparent molar adiabatic compression are likely attributable to changes in water-water interactions. Viscous relaxation time (τ) increases significantly with a rise in bio-surfactant concentration and decreases with increasing temperature, which may be because of structural relaxation processes resulting from molecular rearrangement. All of the estimated parameters have been analysed for their trends with regard to the different patterns of intermolecular interaction present in an aqueous glycyl glycine solution and bio-surfactant system.
Keywords: apparent molar adiabatic compression; apparent molar volume; bio-surfactants; glycyl glycine; intermolecular interactions; isentropic compressibility.