Reversible surface activity and self-assembly behavior and transformation of amphiphilic ionic liquids in water induced by a pillar[5]arene-based host-guest interaction

In this paper, we aimed to develop a reversible and effective method to control the surface activity and self-assembled morphology of amphiphilic imidazolium-type ionic liquids (G) in water. For this purpose, a series of pillar[5]arene/imidazolium supramolecular complexes were designed and prepared. Before the formation of the host-guest complex, the surface activity of G7 worked well, and foams could be generated easily. However, after the addition of water-soluble pillar[5]arene (WP5), the rigid WP5 platform caused steric hindrance that prevented the hydrophobic chains on G7 from getting close to each other, inducing the change in surface activity. On the other hand, because paraquat (PQ) has a larger association constant with WP5 than G7, the surface activity of the solution can be recovered after the addition of PQ. TEM confirmed that self-assembled morphologies of this reversible system transformed from nanoparticles to nanosheets then to nanoparticles. It is anticipated that this supramolecular method for controlling the surface activity of amphiphiles in a reversible way may find application in fields where fast foaming and defoaming are needed. (C) 2018 Elsevier Inc. All rights reserved.