The N-allyl substituted effect on wormlike micelles and salt tolerance of a C 22 -tailed cationic surfactant.

Wormlike micelles (WLMs) have been observed in a wide variety of cationic surfactants. Here we developed WLMs based on an N-allyl substituted cationic surfactant with an unsaturated C22 -tail, N-erucamidopropyl-N,N-dimethyl-N-allyl-ammonium bromide (EDAA), and compared them with UC22 AMPM at the same concentration. The viscoelasticity, aggregate microstructure and salt tolerance of EDAA solutions were investigated by rheology, surface tension and Cryo-TEM measurements. It was found that EDAA exhibited a higher viscosity and a high salt tolerance. Upon increasing the concentration of NaCl, the viscosity of wormlike micelles in the solutions continuously increased and reached ∼1.10 × 106 mP s at 200 mM. On further increasing the NaCl concentration to 2000 mM, the viscosity remained at ∼106 mP s without any reduction. But the viscosity of UC22 AMPM solutions showed a drastic change with the increase of NaCl concentration. This drastic variation in rheological behavior is attributed to the presence of the N-allyl substituent. Besides, the EDAA also shows some advantages such as low overlapping concentration(∼2.2 mM) and stable viscosity over the whole pH range.