Phase behavior of the ternary aqueous mixtures of two polydisperse ethoxylated nonionic surfactants

The phase diagram of the ternary aqueous system composed by two polydisperse ethoxylated surfactants, commercially known as 24-3 and 24-7, with the average molecular formula corresponding to triethylene - and heptaethylene - glycol dodecyl ether, has been developed at 25 °C. The identification of the different lyotropic liquid crystalline (LLC) structures, whose range of stability has been preliminarily determined by visual inspection through cross-polarizers, has been performed using polarized optical microscopy (POM), small angle neutron and X-ray scattering (SANS, SAXS). Data have been analyzed in terms of the combined effects of the different length of poly(oxyethylene) chains of the two surfactants and hydration/dehydration of the polar headgroups, depending on the total surfactant concentration. Peculiar effects of both hydrophobic and hydrophilic chains polydispersity have been highlighted. Our results shed light on the aggregative behavior of surfactant mixtures widely used in homecare detergent formulations.