Rheology study of wormlike micellar solution formed by 1-hexadecyl-3-methylimidazolium tetrafluoroborate ionic liquids in present of sodium salicylate.

The micellar solution of a surface active ionic liquid, 1-hexadecyl-3-methylimidazolium tetrafluoroborate (C₁₆mimBF₄), with the presence of organic salt sodium salicylate (NaSal) was investigated by rheological measurements and ¹HNMR. According to steady-shear viscosity curves, with the increase of NaSal concentration, the zero-shear viscosity η₀ firstly showed an increase which meant the gradual formation of wormlike micelles in solutions (the most optimal concentration of NaSal was 4.5 mM), then η₀ decreased to the previous value which indicated the wormlike micelles were destroyed. And the results of ¹HNMR were further verified the structure transformation. The C₁₆mimBF₄/NaSal solution showed special viscoelastic property with the increase of NaSal concentration. When the linear wormlike micelles formed, the mixture solutions had viscosity (G′<G″). When the branched wormlike micelles formed, the elastic property was prominent (G′>G″). In the frequency sweep rheological measurements, the curves of G′ and G″ showed two intersections, which indicates the structure of long wormlike micelles is weak and may be cut into short ones at higher shear frequency. [ABSTRACT FROM AUTHOR]