Rheological properties of the gels of biological surfactant sodium deoxycholate/amino acids/halide salts systems

Rheological properties of biological surfactant sodium deoxycholate (NaDC) in the presence of two amino acids (l-Lys and l-Arg) and two halide salts (NaCl and NaBr) have been investigated systematically at 20 °C and pH = 6.864. The gel-to-sol transition behavior induced by the addition of amino acids can be observed. It is found that the viscoelasticity of the hydrogels of 50 mmol L−1 NaDC decreased when l-Lysine (l-Lys) or l-Arginine (l-Arg) was added in the system. However, the addition of halide salts NaCl or NaBr in the above system resulted in an opposite trend. In view of these phenomena, a conclusion was given that l-Lys and l-Arg amino acids can destroy the network structure of the hydrogels while NaCl and NaBr can strengthen it. Moreover, it is found that the viscoelasticity of the l-Lys-containing hydrogel is higher than that of l-Arg-containing hydrogel at the same condition, on the other hand, the viscoelasticity of NaCl-containing hydrogel is higher than that of NaBr-containing hydrogel at the same concentration, indicating that NaCl performs better in strengthening the network structure of the hydrogels than NaBr. Furthermore, thixotropic experiments have also been done and revealed that the NaDC hydrogels prepared in this work possessed excellent thixotropic properties, which have potential applications in the field of as smart materials for drug controlled release materials.