title: CO2-induced smart viscoelastic fluids based on mixtures of sodium erucate and triethylamine.
abstract: Simple "green" triggers such as CO2 for switching viscoelastic surfactant solutions between an "on" and "off" state without compromising their inherent properties have been a key focus of research in smart soft matter over the past decade. Here we report a CO2-induced anionic wormlike micellar fluid by introducing triethylamine (TEA) into natural anionic surfactant sodium erucate (NaOEr) at a molar ratio (CNaOEr:CTEA) of 3:10. When CO2 is bubbled, pH of the solution decreases from 12.3 to 10.0, and TEA is protonated into a quaternary ammonium salt, which facilitates the growth of micelles as a hydrotrope by screening electrostatic repulsion between the anionic headgroups in NaOEr molecules, resulting in the formation of wormlike micelles and viscoelasticity buildup; upon removal of CO2, the quaternized TEA is deprotonated back into a non-ionic tertiary amine, thus electrostatic repulsion strengthens and the viscoelastic fluid converting it back to the initial low viscosity spherical micellar solution. Such a reversible sphere-to-worm transition could be repeated several cycles without any loss of response to CO2 in the pH range of 12.3-10.0, but when further bubbling excess CO2 to pH<9.50, the solution transforms into a cloudy dispersion with low viscosity due to the de-neutralization of NaOEr, and this process is irreversible. This study offers a facile way to fabricate smart viscoelastic fluids by incorporating a low-molecular weight CO2-sensitive hydrotrope with conventional long-chain surfactants.
authors.affiliation: Chengdu Institute of Organic Chemistry, Chinese Academy of Sciences, Chengdu 610041, People's Republic of China.
authors.forename: Yongmin
authors.initials: Y
authors.lastname: Zhang
authors.affiliation: Chengdu Institute of Organic Chemistry, Chinese Academy of Sciences, Chengdu 610041, People's Republic of China; Polymer Research Institute, State Key Laboratory of Polymer Materials Engineering, Sichuan University, Chengdu 610065, People's Republic of China. Electronic address: yjfeng@scu.edu.cn.
authors.forename: Yujun
authors.initials: Y
authors.lastname: Feng
keywords: Anionic natural surfactant; CO(2)-trigger; Viscoelastic surfactant fluids; Wormlike micelles