title: Two cloud-point phenomena in tetrabutylammonium perfluorooctanoate aqueous solutions: anomalous temperature-induced phase and structure transitions.
abstract: This paper reported the phase behavior and aggregate structure of tetrabutylammonium perfluorooctanoate (TBPFO), determined by differential scanning calorimeter, electrical conductivity, static/dynamic light scattering, and rheology methods. We found that above a certain concentration the TBPFO solution showed anomalous temperature-dependent phase behavior and structure transitions. Such an ionic surfactant solution exhibits two cloud points. When the temperature was increased, the solution turned from a homogeneous-phase to a liquid-liquid two-phase system, then to another homogeneous-phase, and finally to another liquid-liquid two-phase system. In the first homogeneous-phase region, the aggregates of TBPFO were rodlike micelles and the solution was Newtonian fluid. While in the second homogeneous-phase region, the aggregates of TBPFO were large wormlike micelles, and the solution behaved as pseudoplastic fluid that also exhibited viscoelastic behavior. We thought that the first cloud point might be caused by the "bridge" effect of the tetrabutylammonium counterion between the micelles and the second one by the formation of the micellar network.
authors.affiliation: Institute of Physical Chemistry, Peking University, Beijing 100871, China.
authors.forename: Peng
authors.initials: P
authors.lastname: Yan
authors.forename: Jin
authors.initials: J
authors.lastname: Huang
authors.forename: Run-Chao
authors.initials: RC
authors.lastname: Lu
authors.forename: Chen
authors.initials: C
authors.lastname: Jin
authors.forename: Jin-Xin
authors.initials: JX
authors.lastname: Xiao
authors.forename: Yong-Ming
authors.initials: YM
authors.lastname: Chen
mesh_terms: D002152:Calorimetry, Differential Scanning; D002210:Caprylates / Q000737:chemistry*; D004553:Electric Conductivity; D008027:Light; D015394:Molecular Structure; D000644:Quaternary Ammonium Compounds / Q000737:chemistry*; D012212:Rheology; D012542:Scattering, Radiation; D012996:Solutions; D013696:Temperature; D014867:Water; D005466:Fluorocarbons
chemical_list: D002210:Caprylates; D000644:Quaternary Ammonium Compounds; D012996:Solutions; D014867:Water; C520044:tetrabutylammonium perfluorooctanoate; D005466:Fluorocarbons