Huanquan Sun

Wormlike Micelles Formed by Sodium Erucate in the Presence of a Tetraalkylammonium Hydrotrope

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.

Interfacial dilational rheology related to enhance oil recovery

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.

Effect of Divalent Cationic Ions on the Adsorption Behavior of Zwitterionic Surfactant at Silica/Solution Interface

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.

“Green” anionic wormlike micelles induced by choline

In such application fields as oilwell stimulation, tertiary oil recovery and drug release, environmental-friendly 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.

Aging mechanism of unsaturated long-chain amidosulfobetaine worm fluids at high temperature

Both fundamental and technological research interests have highlighted in recent years a remarkable growing focus on surfactant wormlike micelles. Nevertheless, long-term thermal stability, as well as the corresponding aging mechanism of viscoelastic worm fluids was rarely examined. We report for the first time the high-temperature aging effect on wormlike micellar solutions formed by an unsaturated C22-tailed amidosulfobetaine surfactant in the absence and presence of a reducer, by means of rheological methods, cryo-TEM observations, IR and 1H NMR measurements. It was found that the aging effect mainly resulted from the degradation of the carbon–carbon double bond in the surfactant tail rather than its amido head group; and the addition of a small amount of reducing agent could effectively improve thermal stability of the worm fluids.

Effect of alkyl chain length on the surface dilational rheological and foam properties of N -acyltaurate amphiphiles

The dynamic dilational properties of sodium 2-(2-(alkylaryloxy)-alkylamido)ethanesulfonates (12+nB-Ts) at the air–water interfaces were investigated by drop shape analysis, and their foam properties were also measured. The influences of time and bulk concentration on surface dilational properties were expounded. The results show that the molecular interaction controls the nature of adsorption film during lower concentration range, and the film behaves elastic in nature. During higher concentration range, the diffusion exchange process controls the dynamic dilational properties and the surface film shows remarkable viscoelasticity. An increase in hydrophobic chain length enhances the molecular interaction at low concentration and speeds up the diffusion exchange process at high concentration, which results in the different variations of modulus at different concentration regions. For 12+nB-Ts, too short a chain probably produces bad film elasticity, whereas too great a length produces too fast liquid drainage. Therefore the optimal length in the branched chain leads to the best foam stability.

Interfacial Dilational Properties of Acidic Model Oil and Chemical Flooding Systems

The interfacial dilational properties of lauric acid model oil and chemical flooding systems have been investigated by means of longitudinal method. The influences of acid on the dilational viscoelasticity of partly hydrolyzed polyacrylamide (HPAM) and anionic surfactants (4,5-diheptyl-2-propylbenzene sulfonate 377 and Gemini surfactant C12COONa-p-C9SO3Na) have been expounded. The results show that lauric acid concentration is an important factor in controlling the dilational properties of mixed-adsorption layer. The addition of small amounts of lauric acid to solutions of anionic surfactant appears to increase the dilational modulus, while the superfluous addition could decrease the dilational modulus mainly due to the weakening of strong interaction among long alkyl chains of surfactant molecules. The polymer plays different roles in influencing the nature of adsorbed layers at different lauric acid concentrations: at low concentration, the addition of polymer perhaps weakens the hydrophobic interactions of lauric acid molecules, which results in decreasing the dilational modulus of adsorbed layer. At high concentration, the addition of the polymer increases the dilational modulus due to hydrophobic interactions between polymer and lauric acid molecules. At the same time, the mixed adsorbed layer shows low frequency due to the slow diffusivity of polymer molecules. The addition of lauric acid to polymer-surfactant system will further increases diffusion-exchange process between the interface and the bulk, which consequently leads to the decrease in dilational modulus.