Smart viscoelastic anion polyelectrolyte fluids “crosslinked” by CO2

Abstract

Smart fluids with tunable rheological properties show a wide range of applications in various areas, so they have attracted intense interest. Recently, the viscoelastic fluids with tunable rheological properties, particularly the CO2-triggered smart fluids, have become a popular topic because such reversible change in viscoelasticity conferring them new functions and expanding their applications. Additionally, anioinc polymers can be crosslinked to impart fluids significantly improved rheological properties. Herein, Sodium polyacrylate (NaPAA) and 2,4,6-tris(dimethylaminomethyl)phenol (TAP) are employed to prepare aqueous fluid. The solution properties of the fluid with and without CO2 are examined by steady and dynamical rheology. The effects of NaCl concentration and the ratio of NaPAA/TAP on the rheologies are studied and the interactions between TAP and NaPAA in the absence and presence of CO2 are investigated using pH titration, 1H NMR and cryo-TEM technology. CO2 is able to reversibly change the rheological properties of the fluid via protonating and deprotonating TAP, imparting it smart response. In the absence of NaCl, the introduction of the CO2 reduces the viscosity and elasticity of the fluid as the produced quaternary ammonium salts largely screen the electrostatic repulsions of NaPAA chains. However, in the presence of NaCl, the addition of CO2 greatly enhances the viscoelasticity of the fluid because the protonated TAP strongly interacts with NaPAA forming three-dimensional networks.