Equilibrium between phases in water–protein–surfactant systems

Phase diagrams relative to the systems water–lysozime–lithium perfluorononanoate (H2O–LYS–LiPFN), water–bovine serum albumin–sodium taurodeoxycholate (H2O–BSA–NaTDC), and water–gelatin–Quillaja bark Saponin (H2O–GEL–QBS) have been drawn, at 25 °C. Solutions, gels, multiphase systems and solid particles dispersed in gel have been observed. In all cases the presence of protein–surfactant based gels has been observed. Ionic strength and, to a less extent, pH of the solvent medium reduce the width of the gel phase and are responsible for modifications in the equilibrium solution-disperse solid. Optical microscopy, surface tension, optical turbidity, ionic conductivity, emf, NMR, volumetric and viscosity data have been used to characterise the solution and the multiphase regions occurring in the aforementioned systems. Proper combination of the above findings allows drawing some preliminary hypotheses on the mechanisms responsible for the stability of protein–surfactant based gels.