Influence of pressure and electrolyte on the phase behavior of water-oil-nonionic surfactant systems

The influence of pressure and the lyotropic electrolyte sodium chloride on the phase behavior of water + oil + nonionic surfactant systems was studied. Various phase transitions were observed visually in mixtures of water + phenylalkanes + n-alkyl polyglycol ethers over a temperature range of 280-365 K and a pressure range of 0.1-100 MPa (incidentally, pressures up to 300 MPa were used). Results show that the three-phase region in which three liquid phases are in equilibrium widens with increasing pressure and temperature. At constant temperature phase behavior of the type 2-3-2 was found with increasing pressure. Furthermore, it is shown in systems which do not have a three-phase region at atmospheric conditions that such a region can be induced by increasing the pressure or by adding sodium chloride.