Enhancing Hardness Tolerance of Anionic Surfactants: Effects of Organic Additives on LABS and AOS Systems Studied by Turbidity and Dynamic Light Scattering

The micellar behavior of LABS or AOS or their mixed system was investigated in hardwater. The effect of the presence of EG, PEG, or alcohols on the hardness tolerance of the LABS has been studied. The surfactant solution initially became turbid in hardwater due to the formation insoluble calcium salt of the surfactant, which gradually disappeared with increased surfactant concentration. The turbidity phase diagram of the LABS in hardwater was developed based on the %T of light by the surfactant solution. A sharp increase in the hardness tolerance of LABS was observed in the presence of EG, PEG, or alcohol. Among the additives used, the maximum hardness tolerance was observed in the presence of PEG-400. The DLS pattern of LABS or AOS solution in hardwater showed single exponential decay along with a stretched decay pattern at higher ppm hardwater. Results showed an initial decrease in the size of the LABS aggregates in hardwater of up to about 400 ppm, followed by a sharp increase thereafter due to the formation of the insoluble calcium salt of the surfactant. However, in the presence of EG or isobutanol, a decrease in size was observed, especially at higher ppm hardwater, indicating improved hardness tolerance.