Anionic wormlike micelles, particularly those formed by long-chain carboxylate surfactants, are relatively less documented though their cationic or zwitterionic counterparts are frequently reported. In this study, the wormlike micelles of sodium erucate (NaOEr), a C22-tailed anionic surfactant with a monounsaturated tail, in the presence of a tetraalkylammonium hydrotrope were investigated for the first time. The different effects of two hydrotropes, benzyl trimethyl ammonium bromide (BTAB) and tetramethyl ammonium bromide (TMAB), on the phase behavior and rheological behaviors were compared, and the influences of surfactant concentration and temperature on the rheological properties of NaOEr solutions were also examined. Both organic salts can lower the Krafft temperature of NaOEr solutions and thus improve its water solubility, but BTAB can make T(K) drop more sharply. At a fixed NaOEr concentration, less BTAB is demanded to induce the formation of viscoelastic solution and to obtain the maximum viscosity of NaOEr solution; at a constant salt concentration, with increasing NaOEr content, the NaOEr-BTAB system shows a larger zero-shear viscosity (η(0)), relaxation time, and plateau modulus but lower overlapping concentration than those of the NaOEr-TMAB system. The occurrence of maximum η(0) with increasing salt content for the NaOEr-BTAB system results from the formation of vesicles and L(3) phases, which were verified by cryo-TEM observations. η(0) shows an exponential decrease with increasing temperature; nevertheless it still remains above 10(3) mPa·s even at 90 °C.

Dilational rheology has been proved to be a powerful tool to investigate equilibrium and dynamic properties of adsorption films by recent studies. Interfacial dilational properties play crucial roles in Enhanced oil recovery (EOR) processes, such as the formation of oil bank and the demulsification of crude oil emulsions. Moreover, measurements of the interfacial rheology give important clues about the conformations and molecular interactions of amphiphiles adsorbed at an interface. In this review, the experimental results are summarized on dilational rheology of adsorbed layers containing surfactants and polymers employed in EOR, crude oil components and demulsifiers have been summarized. The relationship between dilational data and emulsion stability has been discussed.

In such application fields as oilwell stimulation, tertiary oil recovery and drug release, environmentalfriendly wormlike micelles are largely preferred. The present work reports a ''green'' wormlike micellar system formed by a bio-based anionic surfactant, sodium erucate (NaOEr), and a biodegradable hydrotrope, choline. The micellar solutions were examined by means of rheology and cryo-TEM observation. Besides possessing lower toxicity, choline exhibits a stronger ability to induce micelle growth than tetramethylammonium, which is commonly used to promote the formation of anionic worms, and the choline-NaOEr system is more thermosensitive with increasing counterion concentration. These notable advantages enable the choline-NaOEr wormlike micellar system to find potential applications in biomedical areas and clean fracturing fluids.

The adsorption behavior of zwitterionic surfactant dodecyl sulfobetaine (DBS) on a silica/solution interface with Ca(2+), Mg(2+) existing in aqueous solution is explored by atomistic molecular simulations. The interaction energy contribution of van der Waals and electrostatic potentials in the surfactants/water/silica system are respectively calculated, from which the electrical interaction can be found to play a decisive role in the adsorption tendency of DBS on the silica surface with or without inorganic ions, despite different mechanisms. The distinct decrease of energy has been found to be derived from electrical interaction when DBS adsorb on the silica surface covered by Ca(2+) or Mg(2+). Therefore, it can be predicted that the cationic ions combined on the negatively charged silica surface in a mineral water medium might decrease the adsorption trend of DBS on the silica surface, which has been experimentally proven by TOC measurement. Structural information of the close interface layer and the distribution of water molecules are analyzed after the complete molecular dynamics simulation using a ternary model. Ca(2+) and Mg(2+) combined on the silica surface can reduce the adsorption amount of DBS by preventing the direct interaction between DBS and surface, and bringing about the orientation reversal of DBS molecules to break the order of adsorption interface layer. Furthermore, changes in the status of the water spreading on the silica surface caused by the complexation of cations are also an important reason in the adsorption reduction.

Polymer flooding (PF) and alkaline/surfactant/polymer (ASP) flooding have been applied throughout the world for more than 20 years.