CO₂-Switchable Viscoelastic Fluids Based on a Pseudogemini Surfactant

Abstract

Recent research has highlighted a growing focus on stimuli-responsive surfactant wormlike micelles (WLMs), particularly those with switchability. Here we report CO2-switchable WLMs based on the commercial anionic surfactant sodium dodecyl sulfate (SDS) and N,N,N',N'-tetramethyl-1,3-propanediamine (TMPDA) mixed in a mole ratio of 2:1. When CO2 is bubbled into an aqueous mixture of these reactants, the TMPDA molecules are protonated to form quaternary ammonium species, two of which in the same protonated TMPDA molecule "bridge" two SDS molecules by noncovalent electrostatic attraction, behaving like a pseudogemini surfactant and forming viscoelastic WLMs as verified by cryo-TEM. Upon removal of CO2, the quaternized spacers are deprotonated back to tertiary amines, dissociating the pseudogeminis back to conventional SDS molecules that form low-viscosity spherical micelles. Such a reversible sphere-to-worm transition could be repeated several cycles without a loss of response to CO2.

CO2-responsive anionic wormlike micelles based on natural erucic acid

“…When the carbon dioxide bubbling time is further extended longer than 10 s, the moduli of the solutions are too low to determine. From these findings shown above, one can deduce that carbon dioxide functions as a thinner to diminish wormlike micelles in the current system rather than a thickening-inducer as observed in SDS-TMPDA, 36 ODPTA, 37 UC22AMPM 38 or C18SNa-DMAE 39 systems reported previously.…”

“…20 Hence, in the present system the viscoelastic fluid cannot be recovered by depleting carbon dioxide with nitrogen, a common way used in other wormlike micellar systems. [36][37][38][39] As displayed in Figure 5, the pH of the 100 mM erucic acid is as low as 4·38 and the dispersion appear opaque. When adjusting the pH of the solution to 11·16 by introducing NaOH at 60°C, the solution transforms into transparent as aforementioned; bubbling carbon dioxide to saturation leads the solution pH to 6·63, and it appears turbid as that of the 100 mM original erucic acid solution; nevertheless, even bubbling nitrogen at 85°C to displace carbon dioxide can only get the pH back to 9·22 (9·72 at 100°C) at which the solution is less viscous though the turbidity is decreased.…”

“…Compared with carbon dioxide-responsive SDS-TMPDA 36 and C18SNa-DMAE systems 39 that were formed by introducing a carbon dioxide-sensitive hydrotrope into surfactant solutions, the wormlike micelles reported here is formed by only utilizing the C 22 -tailed fatty acid itself, without investing any hydrotropes. Such one-component system is of great importance in some applications such as tertiary oil recovery where the wormlike micellar system free of hydrotropes can effectively prevent the 'chromatographic fractionation' from multicomponent displacing fluids.…”

“…[36][37][38] We developed for the first time the carbon dioxide-switchable wormlike micelles, based on the mixture of commercial anionic surfactant sodium dodecyl sulfate (SDS) and N,N,N′,N′-tetramethyl-1,3-propanediamine (TMPDA) with a molar ratio of 2:1. 36 When carbon dioxide is bubbled into the aqueous mixture solution, TMPDA is protonated into quaternary ammonium species, which can 'bridge' two SDS molecules by non-covalent electrostatic attraction, behaving like a 'pseudo' gemini surfactant and forming viscoelastic wormlike micelles. On removing carbon dioxide by nitrogen, the quaternized spacers are deprotonated back into tertiary amines, breaking the 'pseudo' geminis up back to conventional SDS molecules that form lowviscosity spherical micelles.…”

Responsive self-assemblies based on fatty acids

“…Surfactants are going away from the WLMs which result into a transition from WLMs to spherical micelles or free monomers. Usually, a common way to deplete carbon dioxide is to inject nitrogen by bubbling in order to reversibly switch the systems [40,41]. However in this system, bubbling nitrogen cannot make a reversible process since the increase of pH is not high enough to reinitiate the formation of WLMs.…”