Effects of sodium salicylate on the microstructure of a novel zwitterionic gemini surfactant and its rheological responses.

Solutions of a novel zwitterionic gemini surfactant, 1,2-bis[ N-ethyl- N-(sodium 2-hydroxyl-3-sulfopropyl)-dodecyl-ammonium] ethane betaine (DBA), in presence of sodium salicylate (NaSal) can form wormlike micelles and thereby show a viscoelasticity. At low molar ratio of NaSal/DBA, R ≤ 0.3, the systems behaved like a Newton fluid. However, as the R increased, the systems exhibited shear-thinning behavior. The zero-shear viscosity η increased dramatically with increasing R and peaked with R = 0.8 at a value of 18.8 Pa s. This was attributed to the formation of long wormlike micelles (1.6 ∼ 2.9 μm) and network structure confirmed by scanning electron microscopy. Further increase in R beyond 0.8 resulted in a slight decrease in η, which may be caused by the branched micelles formed at high salt concentration. In addition, the tested systems showed a Maxwellian behavior at lower frequencies, but deviated from the Maxwellian mode at higher frequencies. [ABSTRACT FROM AUTHOR]