Xuepeng Wu

Investigation of Novel Triple-Responsive Wormlike Micelles

Smart wormlike micelles with stimuli-tunable rheological properties may be useful in a variety of applications, such as in molecular devices and sensors. The formation of triplestimuli-responsive systems so far has been a challenging and important issue. In this work, a novel triplestimuli (photo-, pH-, and thermoresponsive) wormlike micelle is constructed with N-cetyl-N-methylmorpholinium bromide and trans-cinnamic acid (CA). The corresponding multiresponsive behaviors of wormlike micellar system were revealed using cryogenic transmission electron microscopy, a rheometer, and 1H NMR. The rheological properties of wormlike micellar system under different temperatures, pH conditions, and UV irradiation times are measured. As confirmed by 1H NMR, chemical structure of a CA molecule can be altered by the multiple stimulation from an exotic environment. We expect it to be a good model for triple-responsive wormlike micelles, which is helpful to understand the mechanism of triple-responsiveness and widen their applications.

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.

Design and Study of a Novel Thermal-Resistant and Shear-Stable Amphoteric Polyacrylamide in High-Salinity Solution

Water-soluble polymers are widely used in oilfields. The rheological behaviors of these polymers in high-salinity solution are very important for stimulation of high-salinity reservoirs. In this work, a novel thermal-resistant and shear-stable amphoteric polyacrylamide (PASD), prepared from acrylamide (AM), sodium styrene sulfonate (SSS), and acryloxyethyl trimethylammonium chloride (DAC) monomers, was prepared by free-radical polymerization in high-salinity solution. The amphoteric polyacrylamide was characterized by Fourier transform infrared (FTIR) spectroscopy, nuclear magnetic resonance spectroscopy (1H NMR), elemental analysis, thermogravimetric analysis (TG), and scanning electron microscopy (SEM). The amphoteric polyacrylamide exhibited excellent salinity tolerance. The slow increase in apparent viscosity of the polymer with increase in salinity was interesting. The amphoteric polyacrylamide showed perfect temperature resistance in high-salinity solution. The viscosity retention reached 38.9% at 120 °C and was restored to 87.8% of its initial viscosity when temperature was decreased to room temperature. The retention ratio of apparent viscosity reached 49.7% at 170 s−1 and could still retain it at 25.8% at 1000 s−1. All these results demonstrated that PASD had excellent thermal-resistance and shear-stability in high-salinity solution. We expect that this work could provide a new strategy to design polymers with excellent salinity-tolerance, thermal-resistance, and shear-stability performances.

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.

Developing New Recyclable and pH-Sensitive Amphiphile for Heavy Oil Emulsion and Demulsification: A Molecular Dynamics Study

We report a long-chain N-alkyl-N, N-dihydroxyethylammonium salt (ADHA) that can be reversibly transformed into charged surfactants by decreasing pH, thereby stabilizing(or destabilizing) water/oil emulsions. As the conventional oil reserves in the world continue to decline, the immense deposits of heavy crude oil attract much attention. A growing number of heavy oil reservoirs are being proven and developed. However, heavy oil’s recovery and pipeline transport pose new challenges due to its high viscosity. The emulsion of heavy oil by surfactant floods is able to lower the viscosity but consequently leads to oil–water separation problem. Therefore, the application of this technique will benefit from an efficient, rapid method of demulsification at specially desired stage, which raises stringent requirements to the surfactants. The increase of the pH reverses the reaction, deprotonates the surfactants into uncharged tert-ammonia (ADHA), and destabilizes the emulsion. In addition, the introduction of two hydroxyls in the head groups reduces the lipophilic of the ADHA. Hence, it is inclined to flocculate in water when the base is added and it is simple to realize the recycle of the surfactant. MD simulations are used to study the mechanisms of this novel surfactant. Demulsification was studied in a beaker; the emulsion separates into two layers within 3 min, revealing the ADHA’s function as a demulsifier. Aiming for deeper insights into the mechanisms of the transformation of ADHA, using MD simulation tools, we studied the behavior and properties of ADHA at the oil–water interface. Computational results suggest cohesive bindings with experimental outcomes and also give qualitative and quantitative explanations at molecular level. In summaries, these emulsion–demulsification processes suggest that the switchable surfactants are potentially useful for heavy oil production and pipeline transports.

Study on Synthesis and Properties of Gemini Surfactant Used as Viscoelastic Surfactant (VES)

As one kind of the new surfactants with novel structure, higher surface activity, lower critical micelle concentration, and lower Krafft point, the quaternary ammonium gemini surfactants have a promising application prospect in viscoelastic surfactant (VES). In this paper, one kind of viscoelastic cationic gemini surfactant was synthesized through using N,N-dimethyl-1, 3-propane diamine, octadecanoic acid, and 1,4-dibromobutane. The molecular structure of the surfactant was characterized by 1H NMR, the self-assembly structure was observed by atomic force microscopy, and the viscoelasticity behavior was measured through rheological measurements. The study shows that the gemini surfactant can form self-assembled structures in single system, and the molecular self-assembly driven by the non-covalent interactions can provide the foundation for building well-defined structures in the nanometer or micrometer length scale. In addition, stable viscoelastic behavior was observed in the surfactant system, with strong binding energy and electrostatic interactions. This work can reveal the interaction mechanism between the molecules and the synergistic interactions of various non-covalent forces at molecular level, which is significant to study the viscoelastic surfactant used in clean fracturing fluid.

Novel investigation based on cationic modified starch with residual anionic polymer for enhanced oil recovery

ABSTRACT Cationic modified starch polymer (CMSP) is a newly developed green chemical agent designed to reutilize the residual anionic polymer found in reservoirs for enhanced oil recovery (EOR). In this study, a series of experiments were conducted to investigate the phase behavior of the residual anionic polymer, CMSP solution, and the flocculation generated from the mixture in plugging capacity and capability of enhancing oil recovery in heterogeneous reservoirs. The experiment results show that the phase behavior of the residual anionic polymer and CMSP solution could be divided into two parts: rapid flocculation reaction and dispersion reaction. The main mechanisms of the rapid flocculation reaction were charge neutralization and bridging. Based on the above results, an optimal amount of CMSP was chosen for plugging capacity, stability, and EOR study. Plugging tests in both parallel cores and EOR in three-layer heterogeneous square cores illustrate that the injected CMSP slug after polymer flooding can effectively block the high-permeability zone and initiate the remaining oil in middle- to low-permeability zones. The investigation results prove that the CMSP solution, injected after polymer flooding, reduces the pollution of produced fluid and further improves oil recovery. GRAPHICAL ABSTRACT