Experiments, molecular dynamics simulations, and quantum chemistry calculations on the effect of gemini surfactants' headgroup on the oil-water interfacial tension.

The effect of the Gemini surfactant headgroup on the oil-water interfacial tension has yet to be systematically revealed. In this work, anionic Gemini surfactants with different hydrophilic headgroups (carboxylic, sulfuric, and sulfonic) were designed and synthesized. The oil-water interfacial tension was tested. The essential parameters for evaluating the interface characteristics, including the oil-water interfacial layer thickness, the coordination number, and the diffusion coefficient, were calculated employing molecular dynamics simulation. The surface electrostatic potential explained the quantitative mechanism of the hydrophobicity and lipophilicity of three types of Gemini surfactants through quantum chemical calculations. The oil-water interfacial tension difference of the Gemini surfactants was revealed at the electronic level. This paper will provide theoretical guidance for designing Gemini surfactants with a high-efficiency performance to enhance oil recovery.

Rheological characterizations and molecular dynamics simulations of self-assembly in an anionic/cationic surfactant mixture.

The formation of self-assemblies in mixed amino acid-based anionic N-hexadecanoylglutamic acid (HGA) and cationic benzyldimethyl hexadecylammonium chloride (HDBAC) surfactants in aqueous solutions has been characterized. With rheological analysis, the viscoelastic properties of the mixed system are found to be completely dependent on the concentration of HDBAC. Molecular dynamics simulation results suggest that the morphology of self-assembly can be regulated from spherical micelles to wormlike micelles by the addition of HDBAC. The aromatic group of HDBAC adsorption provides a "charge-neutral" function to the micelle corona; the repulsive interactions within the head group of HGA are progressively screened and closely packed. In addition, the dynamic processes and formation mechanisms of self-assembly were analyzed in detail with molecular simulation techniques.

Performance Evaluation and Mechanism Study of Seawater-Based Circulatory Fracturing Fluid Based on pH-Regulated WormLike Micelles.

In this article, a novel salt-resistant pH-sensitive surfactant N-carboxystearamido methanesulfonic acid (MSA) was designed and synthesized. The rheological properties of the MSA/CTAB mixed system prepared using seawater were evaluated, and the variation laws of the related rheological parameters were discussed. The relevant fracturing technical parameters of the MSA/CTAB mixed system were comprehensively evaluated. The wormlike micelles formed by the non-covalent binding of MSA and CTAB molecules can resist the electrostatic effect of inorganic salts in the seawater. Meanwhile, the MSA/CTAB mixed system has an excellent pH response and revealed that the change from wormlike micelles to spherical micelles leads to the decrease of the apparent viscosity and the transition from Maxwell fluid to Newton-type fluid. Furthermore, the MSA/CTAB mixed system has excellent cyclic fracturing performance, which can meet the dual requirements of fracturing fluid cost and performance of offshore oilfield, and has a good application prospect.

Study of the formation and solution properties of worm-like micelles formed using both N-hexadecyl-N-methylpiperidinium bromide-based cationic surfactant and anionic surfactant.

The viscoelastic properties of worm-like micelles formed by mixing the cationic surfactant N-hexadecyl-N-methylpiperidinium bromide (C16MDB) with the anionic surfactant sodium laurate (SL) in aqueous solutions were investigated using rheological measurements. The effects of sodium laurate and temperature on the worm-like micelles and the mechanism of the observed shear thinning phenomenon and pseudoplastic behavior were systematically investigated. Additionally, cryogenic transmission electron microscopy images further ascertained existence of entangled worm-like micelles.

Formation of worm-like micelles in mixed N-hexadecyl-N-methylpyrrolidinium bromide-based cationic surfactant and anionic surfactant systems.

Through the descriptive and rheological characterization of worm-like micelles formed by N-hexadecyl-N-methylpyrrolidinium bromide and sodium laurate, the formation and properties of the worm-like micelles were affected by the concentrations of sodium laurate and temperature. Additionally, cryogenic transmission electron microscopy images further validated the formation of worm-like micelles.