Methodology for the investigation of surfactant dissolution in water

Concentrated aqueous solutions of surfactants pastes are widely used in industrial productions. The dissolution phenomena of these fluids in water is difficult to optimize, given the thermodynamic complexity of the system, that adds further resistance to the mass transport efficiency. One of the most common anionic surfactants is Sodium Lauryl Ether Sulphate (SLE3S). Depending on the SLE3S-water composition, surfactant nano-molecules can assume different morphologies, such as micellar phases (<30%wt of SLE3S), hexagonal liquid crystals (>30%wt), cubic structures (~60%wt), or lamellar liquid crystals (>60%wt), which are characterized by nanoscale ordered structures. Different phases show strongly different rheological behaviour. All phases are non-Newtonian, with a shear-thinning viscosity as function of imposed shear rate. A novel methodology is here proposed to investigate the dynamic evolution of the phase changes during surfactant dissolution using Time-lapse microscopy. Samples are observed trough crossed polarizers. Differences in nano-morphology, due to molecules rearrangement during phase changes, can be easily monitored by measuring light intensity profiles.