Mingyong Du

The structure effect on the surface and interfacial properties of zwitterionic sulfobetaine surfactants for enhanced oil recovery

The surface and interfacial properties of five zwitterionic surfactants, including three propyl sulfobetaines CSB (where the carbon atom number of the alkyl chain is 12, 14 and 16, respectively) and two hydroxypropyl sulfobetaine surfactants CHSB (where the carbon atom number of the alkyl chain is 12 and 14, respectively), were studied at both air–water and oil–water interfaces. The surface activity of these surfactants at the air–water interface in aqueous solutions was investigated by the Wilhelmy plate method at 30 °C and ambient pressure. The values of the critical micelle concentration (CMC) and surface tension at CMC (γCMC) were determined from the surface tension measurements. The obtained results indicate that CMC and surface tension strongly depend on the surfactant molecular structure. An increase in the alkyl chain length results in a decrease in the CMC and γCMC values. The presence of a hydroxyl group causes an increase in CMC values and a decrease in γCMC values. The hydroxypropyl sulfobetaine surfactants have better surfacial properties. In addition, the interfacial activity at the oil–water interface among the crude oil–reservoir water–surfactant systems was investigated by use of the spinning drop method under harsh reservoir conditions of high temperature (90 °C) and high salinity (11.52 × 104 ppm, including 7040 ppm Ca2+ and 614 ppm Mg2+). It is interesting that the transient minimum dynamic interfacial tension (DITmin) could be observed in a specific concentration range. The time to reach DITmin is different with different surfactant molecular structures and surfactant concentrations. The hydroxypropyl sulfobetaine surfactant C14HSB shows excellent interfacial properties: it can reduce interfacial tension (IFT) between oil and water to an ultralow level at a very low concentration, and the ultralow IFT phenomenon only occurs in a specific concentration range from 0.03 to 0.10 wt%. In this work, hydroxypropyl sulfobetaine surfactants exhibit remarkable ability and are good candidates for chemical agents to enhance oil recovery in harsh reservoirs.

Formation and rheological properties of wormlike micelles by N-hexadecyl-N-methylpiperidinium bromide and sodium salicylate

The formation and properties of wormlike micelles composed of a surface-active surfactant N-hexadecyl-N-methylpiperidinium bromide (C16MDB) and organic salt sodium salicylate (NaSal) at room temperature were studied. Rheological measurements and cryogenic transmission electron microscopy (cryo-TEM) were conducted to study the rheological properties and microstructures of wormlike micelles. Cryo-TEM image confirms the formation of wormlike micelles in aqueous solution. Rheological results show that wormlike micelles indicate linear viscoelasticity and follow the Maxwell model. The Cole–Cole plots agree well with the typical characteristic of the Maxwell model at low and middle frequencies. The contour length, mesh size, and entanglement length of wormlike micelles are estimated from the rheological measurements. In addition, the temperature effect on the rheological properties of wormlike micelles is also studied. Through comparison, the entanglement length and mesh size of wormlike micelles are nearly unchanged, while the contour length shows a sharp decrease tendency with the increase of temperature, indicating that the change of rheological properties with the temperature is due to the contour length change of wormlike micelles.

Study of micelle formation by fluorocarbon surfactant N-(2-hydroxypropyl)perfluorooctane amide in aqueous solution.

Micelles formed by fluorocarbon surfactant N-(2-hydroxypropyl)perfluorooctane amide in aqueous solution were studied through surface tension, dynamic light scatting (DLS), isothermal titration calorimetry (ITC), and dissipative particle dynamic (DPD) simulations. Through surface tension measurements, the effectiveness of surface tension reduction, the maximum surface excess concentration, and the minimum area occupied per surfactant molecule at the air/water interface were investigated. The critical micelle concentration (cmc) at different temperatures and a series of thermodynamic parameters (ΔG(m)0, ΔH(m)0, ΔS(m)0, ΔG(ads)0, ΔH(m)(A) and ΔC(p(m))0) of micellization were evaluated. The thermodynamic parameters showed that the micelle formation was entropy-driven. The micelle formation was also confirmed by ITC and DLS. In addition, the DPD simulations were conducted to simulate the whole process of micelle formation to make micelle formation better understood.

Thermal and pH dual stimulated wormlike micelle in aqueous N-cetyl-N-methylpyrrolidinium bromide cationic surfactant-aromatic dibasic acid system

Dual-stimulated wormlike micelles regulated by pH and temperature in a surface active ionic liquid system comprising of a cationic surfactant (N-cetyl-N-methylpyrrolidinium bromide (C16MDB)) and an aromatic dibasic acid (pyrocatechol) were investigated. Such a system can be reversibly switched between liquid-like and gel-like states on adjusting the solution pH value. The rheology, light scattering techniques and cryogenic-transmission electron microscopy (cryo-TEM) results show the growth of spherical micelles into long and entangled wormlike micelles was responsible for the changes in flow properties such as high viscosity, shear-thinning behaviour and Maxwell-type dynamic rheology. The nuclear magnetic resonance results reveal the binding capacity of pyrocatechol to C16MDB is proposed as the key factor of the unusual rheological and micellar responses of this pH-stimulated system. In addition, with the increase of temperature, molecular motion of surfactant molecules becomes more active, which endow the property of thermo-stimulated to the surface active ionic liquid system.

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.

Aggregation behavior of long-chain piperidinium ionic liquids in ethylammonium nitrate.

Micelles formed by the long-chain piperidinium ionic liquids (ILs) N-alkyl-N-methylpiperidinium bromide of general formula CnPDB (n = 12, 14, 16) in ethylammonium nitrate (EAN) were investigated through surface tension and dissipative particle dynamics (DPD) simulations. Through surface tension measurements, the critical micelle concentration (cmc), the effectiveness of surface tension reduction (Πcmc), the maximum excess surface concentration (Гmax) and the minimum area occupied per surfactant molecule (Amin) can be obtained. A series of thermodynamic parameters (ΔGm0, ΔHm0 and ΔSm0) of micellization can be calculated and the results showed that the micellization was entropy-driven. In addition, the DPD simulation was performed to simulate the whole aggregation process behavior to better reveal the micelle formation process.

Investigation on the aggregation behavior of photo-responsive system composed of 1-hexadecyl-3-methylimidazolium bromide and 2-methoxycinnamic acid

A novel fluid system composed of 2-methoxycinnamic acid (trans-OMCA) and 1-hexadecyl-3-methylimidazolium bromide (C16mimBr) in an aqueous solution was investigated. The compounds trans-OMCA and C16mimBr in an aqueous solution can self-assemble and form viscoelastic worm-like micelles. The concentrations of trans-OMCA and C16mimBr have a significant influence on the rheological properties of the system. The samples were characterized by rheological measurements. The structural isomerization of trans-to-cis for trans-OMCA occurred after UV light irradiation. The transformation of the system after UV light irradiation was determined by UV-vis absorption spectroscopy, rheological measurement and cryo-TEM observation. Surface tension measurements were carried out to investigate the role of trans-OMCA and UV light in C16mimBr aqueous solution. Critical aggregation concentration (cac), effectiveness of surface tension reduction (Πcac), maximum excess surface concentration (Γmax) and minimum area occupied per surfactant molecule (as) were investigated. Critical packing parameter was introduced to express the mechanism of aggregation behavior transition.

Study of pH-responsive surface active ionic liquids: the formation of spherical and wormlike micelles

A noncovalent bonding method is utilized for forming pH-responsive surface active ionic liquids in mixed N-hexadecyl-N-methylpyrrolidinium bromide-based cationic surfactant (C16MPBr) and potassium phthalic acid (PPA). Rheology, cryogenic-transmission electron microscopy, and dynamic light scattering results revealed that the microstructure transition between spherical micelles and wormlike micelles was the fundamental cause of the pH-sensitive rheological properties. In addition, combined with nuclear magnetic resonance and UV–vis analysis, we found that the structure transition of micelles was attributed to different binding abilities of hydrotropes to C16MPBr as pH varies. It is confirmed that the binding ability of PPA to C16MPBr is strongest. This noncovalent bonding method is not only versatile but also economical for fabricating pH-responsive surface active ionic liquids.