title: The Formation of pH-Sensitive Wormlike Micelles in Ionic Liquids Driven by the Binding Ability of Anthranilic Acid.
abstract: Wormlike micelles are typically formed by mixing cationic and anionic surfactants because of attractive interactions in oppositely charged head-groups. The structural transitions of wormlike micelles triggered by pH in ionic liquids composed of N-alkyl-N-methylpyrrolidinium bromide-based ILs (ionic liquids) and anthranilic acid were investigated. These structures were found responsible for the variations in flow properties identified by rheology and dynamic light scattering, and account for the structures observed with cryogenic transmission electron microscopy (Cryo-TEM). High-viscosity, shear-thinning behavior, and Maxwell-type dynamic rheology shown by the system at certain pH values suggested that spherical micelles grow into entangled wormlike micelles. Light scattering profiles also supported the notion of pH-sensitive microstructural transitions in the solution. Cryo-TEM images confirmed the presence of spherical micelles in the low-viscosity sample and entangled wormlike micelles in the peak viscosity sample. Nuclear magnetic resonance spectroscopy analysis revealed that the pH sensitivity of ionic liquid systems originated from the pH-dependent binding ability of anthranilic acid to the cationic headgroup of ionic liquids.
authors.affiliation: School of Energy Resources, China University of Geosciences, Beijing 100083, China. youqing@cugb.edu.cn.
authors.forename: Qing
authors.initials: Q
authors.lastname: You
authors.affiliation: School of Energy Resources, China University of Geosciences, Beijing 100083, China. zgsydxzy@163.com.
authors.forename: Yan
authors.initials: Y
authors.lastname: Zhang
authors.affiliation: School of Energy Resources, China University of Geosciences, Beijing 100083, China. agewanghuan@163.com.
authors.forename: Huan
authors.initials: H
authors.lastname: Wang
authors.affiliation: School of Energy Resources, China University of Geosciences, Beijing 100083, China. fanhongfu@126.com.
authors.forename: Hongfu
authors.initials: H
authors.lastname: Fan
authors.affiliation: School of Energy Resources, China University of Geosciences, Beijing 100083, China. guojp@cugb.edu.cn.
authors.forename: Jianping
authors.initials: J
authors.lastname: Guo
authors.affiliation: Sinopec Shengli Oilfield Research Institute of Petroleum Engineering, Dongying 257000, China. liming521.slyt@sinopec.com.
authors.forename: Ming
authors.initials: M
authors.lastname: Li
mesh_terms: D006863:Hydrogen-Ion Concentration; D052578:Ionic Liquids / Q000737:chemistry*; D008823:Micelles; D012212:Rheology; D062367:ortho-Aminobenzoates / Q000737:chemistry*
chemical_list: D052578:Ionic Liquids; D008823:Micelles; D062367:ortho-Aminobenzoates; C031385:anthranilic acid
keywords: formation mechanism; morphological variation; pH-sensitive; rheology; wormlike micelles