Saturated C22-tailed cationic surfactant in concentrated brine: Structural evolution of wormlike micelles and rheological properties

Abstract

Saturated C22-tailed ultra-long-chain imparts cationic surfactant stable chemical structure and strong hydrophobic interaction that favors the generation of wormlike micelles in brine. Such viscoelastic wormlike micellar fluid is expected to exhibit excellent salt-resistance and temperature-resistance. In this work, the self-assembled microstructures and microscopic flow properties of docosyl(trimethyl)azanium chloride (DCTAC) NaCl solutions were systematically investigated by means of cryogenic transmission electron microscopy (cryo-TEM), rheo-small angle neutron scattering (rheo-SANS), steady-state and dynamic rheology. It is found that DCTAC forms long, linear or branched, flexible or stiff wormlike micelles depending on NaCl concentration. The increase in salt content simultaneously promotes the growth of worm length and the formation of branches. While the worm chain elongation plays a dominant role in mid-range of NaCl concentrations, the branching formation acts as a leading role in supper high NaCl concentrations, which results in rheological properties experiencing a significant increase followed by a certain decrease upon increasing NaCl content up to ∼ 20 wt%. Moreover, DCTAC shows much better thickening power than corresponding homologue surfactants bearing shorter hydrophobic tail in brine, and DCTAC solution also shows much better temperature-resistance than them. These findings are helpful to understand salt effect on cationic surfactant self-assemble behavior, and the relationship between microstructure and solution macroscopical properties.