Ionic Liquid Induced Transition from Wormlike to Rod or Spherical Micelles in Mixed Nonionic Surfactant Systems

The structural changes of wormlike micelles composed of Tween 80 and Brij 30 in the presence of a common ionic liquid 1-butyl-3-methylimidazolium tetralluoroborate (bmimBF(4)) were studied. Upon addition of bmimBF4, the viscosities of the wormlike micelle systems decrease, or in other words, more Brij 30 is needed to attain a similar viscosity value. The changes of the storage/loss modulus and the relaxation time also show that the viscoelastic properties of the wormlike micelles decrease with increasing bmimBF4 concentration. We believe that these results are attributed to a wormlike-rod/spherical micellar transition in the wormlike micelle solution, which is further confirmed by freeze-fracture transmission electron microscopy (FF-TEM) images. Additionally, the location of bmimBF4 in mixed micelles was also studied to explain the structure transition in the above systems.