Sodium Alkyl Ether Sulfonates (SAES): Dual Anionic-Nonionic Behavior in Synthetic Brine Having High Salinity and Hardness

Due to the presence of non-sulfonated residual alkyl ether (AE), sodium alkyl ether sulfonate (SAES) may exhibit clear point-cloud point solubilization behavior in brine. Accordingly, the effect of temperature on the compatibility of iC17EOxS (x = 7 and 10), nC₁₇EO10S, along with their analogous nonionic surfactants iC₁₇EOxH (x = 7 and 10) and nC17EO10, in addition to iC9EO14 in brine has been investigated. Depending on their molecular structures, these surfactants exhibited concentration-dependent clear point and cloud point solubilization behavior. The cloud point was associated with the AE component whereas the clear point was attributed to the sulfonated one. Interestingly, an increase in the cloud point of the nonionic component with respect to the corresponding nonionic AE (100 % active) was observed. Adding iC9EO14 (100 % active) to iC17EO7S (x_an = 0.0-0.362) resulted in a significant decrease in the clear point of iC17EO7S from above 100°C to below 22°C with a concomitant increase in iC17EO7/iC9EO14 mixture cloud point from 68°C. (x_an = 0) to 72°C (x_an = 0.325). This relatively modest increase by 4°C was attributed to the interrelationship of different competitive mechanisms, namely an increase in mixed micelle charge with increasing x_an, the dehydration of OE groups via ion (SO₃^-)-dipole (O → CH₂) interactions, and possible shielding of SO₃^- groups by iC9EO14 nearby extended EO groups. To the best of our knowledge, this is the first instance where dual anionic-nonionic solubilization behavior of SAES in brine characterized by high salinity and hardness is being reported.