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.

Clouding behaviour in surfactant systems

“…Tetrabutylammonium perfluorooctanoate (TBPFO), an ionic surfactant, exhibits two cloud points [29]. When the temperature was increased, the solution turned from a homogeneous phase to a liquidliquid two-phase system, then to another homogeneous phase, and finally to another liquid-liquid two-phase system.…”

“…TBPFO being an anionic fluorinated surfactant exhibits the lower consolute behaviour above its CMC, at 2.3 mM, at 25°C. However, the novelty of this surfactant is the manifestation of two cloud points [29] in aqueous solution beyond a certain critical concentration at approximately 15 mM, like some nonionic surfactant [51]. With the rise in temperature TBPFO solution turned from a transparent homogeneous phase to a liquid-liquid two-phase, then to another homogeneous phase, and finally to another liquid-liquid two phase.…”

Energetics of anionic surfactant-additive systems at the cloud point

“…The role of oscillations in the critical concentration and of micellar growth as mechanisms for the clouding phenomenon is still a controversial issue [12,13]. It is well established that the addition of ionic surfactants increases the cloud points of their nonionic counterparts [14,15] and this increase depends on composition of the mixed micelles. Valaulikar and Manohar [16] have demon strated that the increase in cloud point can be described in terms of the surface charge per micelle, which is responsible for electrostatic repulsion between the micelles.…”

The Clouding Phenomenon for Anionic Sodium Dodecyl Sulfate + Quaternary Bromides in Polar Nonaqueous‐Water‐Mixed Solvents

“…However, aqueous solutions of some ionic surfactants did exhibit the CP behavior in the presence of quaternary bromides having R C C 4 H 9 . The mechanism of the behavior is still an unexplained and challenging task in surfactant research [16][17][18].…”