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The surface active ionic liquids (SAILs) have been widely employed in various aspects of the petroleum industry, and the mixed surfactant systems exhibited greater interfacial activity in enhanced oil recovery (EOR). To systematically explore the effects of the molecular structure and the intermolecular interaction on the interfacial activity of the mixed SAIL/surfactant systems, the interfacial properties of various SAIL/surfactant mixtures containing typical cationic SAILs (N-dodecyl-N-methylpyrrolidinium bromide (L12), 1-dodecyl-3-methylimidazolium bromide (M12), or 1-hexadecyl-3-methylpyrrolidinium bromide (L16)) and anionic surfactants (sodium dodecyl sulfate (SDS) or sodium dodecyl benzene sulfonate (SDBS)) with different molar ratios were investigated. The temperature and salt tolerances of various SAIL/surfactant systems were also investigated. A series of core flooding experiments were carried out to verify the advantages of the mixed SAIL/surfactant systems. It was found that both M12/SDS and L12/SDS mixtures could greatly decrease the IFT to about 10−2 mN/m at the SAIL/surfactant molar ratio of 1:2, whereas the moderate interfacial activity of other systems might be attributed to the poor matching degree of molecular structures and weak intermolecular interaction between SAIL and surfactant. The mixed systems showed superior oil displacement efficiency than single component systems, and the oil recovery was further improved with additional polymer and sodium chloride. The present study demonstrated the mixed SAIL/surfactant systems are efficient and promising chemical flooding agents for EOR application in harsh conditions. [ABSTRACT FROM AUTHOR]

[Display omitted] • A novel ammonium-derived dihydroxyl ionic liquid (DHIL) was synthesized. • The steric hindrance of enlarged headgroups impeded the tight alignment of ILs. • Both dihydroxyl and long alkyl chains highly improved the corrosion inhibition efficiency. • The inhibition mechanism was explained via a combination of experiments and molecular dynamics simulation. A novel ammonium-derived dihydroxyl ionic liquid ([C 16 DPOA]Br) and a control ionic liquid ([C 16 DPA]Br) are synthesized to reveal the effect of dihydroxyl and head groups on their inhibition property via the weight-loss method, surface analysis, electrochemical measurements, and adsorption isotherm studies. [C 16 DPOA]Br exhibits the optimal inhibition ability (93.47 %) for mild steel in 1 M HCl in contrast to [C 16 DPA]Br (88.03 %) and the traditional cationic surfactant CTAB (92.34 %). Based on the experimental results, it can be inferred that the short alkyl chain (propyl) impedes the tight alignment of [C 16 DPA]Br on the metal surface and the interactions between hydroxyl and iron atoms enable [C 16 DPOA]Br to overcome the negative effects of the short alkyl chain on the inhibition property. Finally, molecular electrostatic potential (MEP) distribution and molecular dynamics (MD) simulation verify the reactive sites and adsorption capacity of corrosion inhibitors from the microscopic scale, which further confirms the proposed mechanism. This study focuses on the significance of dihydroxyl and head groups on the inhibition property and provides unique insights into the development of efficient ionic liquid corrosion inhibitors. [ABSTRACT FROM AUTHOR]

[Display omitted] • Two novel PBILs with hydrophobic long alkyl chains were synthesized. • PBILs could effectively inhibit the corrosion of MS in 1 M HCl solution at only 10 μM. • The protection performance of 10 μM PBILs was better than that of 500 μM traditional IL. • MD simulation showed that the π-π stacking strengthen the adsorption film intensity. The ionic liquids (ILs) are regarded as the ideal candidate for the novel and high-efficiency corrosion inhibitors. While the cost problem caused by relatively large dosage limited the wide employments of conventional ILs. In the current study, we synthesized two novel phosphorus-based ionic liquids (PBILs) with different alkyl chain length (dodecyltriphenylphosphonium bromide (C 12 TPB) and cetyltriphenylphosphonium bromide (C 16 TPB)), and evaluated their anticorrosion efficiencies for mild steel (MS) in 1 M HCl aqueous solution by weight loss measurement, scanning electron microscope, X-ray photoelectron spectroscopy and electrochemical test. The results revealed that PBILs performed excellently (inhibition efficiencies > 93 %) at a very low concentration of 10 μM, which was much greater than those for traditional imidazole and pyridine ionic liquids at 500 μM. It was demonstrated that PBILs could adsorb on the metal surface to form the protective film, which should be mixed corrosion inhibitors with cathodic advantage. Then the adsorption study and molecular dynamics simulation confirmed that their special molecular structure highly promoted the intensity of the adsorption film mainly caused by the chemical adsorption. This study provided a novel approach for the structural design and development of high-performance IL corrosion inhibitors. [ABSTRACT FROM AUTHOR]

A typical anionic surface active ionic liquid (SAIL), 1-butyl-3-methyl-imidazolium dioctylsulfosuccinate (BMOT), was introduced to chemical enhanced oil recovery. The ability of BMOT to reduce the interfacial tension (IFT) of water/crude oil was evaluated for its potential application in surfactant flooding. Compared with the traditional anionic surfactant AOT and another anionic SAIL 1-butyl-3-methylimidazolium dodecyl sulfate used in the control experiments, the effects of intramolecular electrostatic attraction and size match were employed to interpret the high interfacial activity of BMOT. The effects of salt and temperature on the water/crude oil IFT further verified the proposed mechanisms. Moreover, BMOT exhibited a satisfactory displacement performance to greatly improve the crude oil recovery (12.5% of the initial oil in place) in core flooding tests. [ABSTRACT FROM AUTHOR]

Ionic liquids (ILs) are incredibly efficient additives to solve wellbore instability resulting from shale hydration. The influence of the molecular structure of ILs on their inhibition performance has been investigated intensively, and hydroxyl is regarded as the significant group to improve their inhibition performances. In this study, three novel dihydroxyl ionic liquids (DHILs) including [C 4 DIPA]Br, [C 8 DIPA]Br, and [C 12 DIPA]Br were successfully synthesized. Then their thixotropy and inhibition properties were evaluated via three-interval thixotropy tests (3ITTs), hot-rolling recovery tests, immersion tests, and linear swelling tests. [C 12 DIPA]Br exhibited the optimal inhibition ability at a low concentration (0.5 wt%) and was more effective than the conventional inhibitor KCl (2 wt%). Various techniques were used to analyze the inhibition mechanism of DHILs including contact angle measurements, zeta potential, X-ray diffraction, and Flourier transform infrared spectroscopy. The results demonstrated that the synergistic effects of hydrogen bonding, electrostatic interaction, and hydrophobic shield should be responsible for the excellent inhibition performance and great thermal stability of [C 12 DIPA]Br. Finally, the proposed mechanism was supported by the control experiments using other three ILs inhibitors and molecular dynamics simulation. Our work provided unique perspectives on developing rationally designed and efficient ILs inhibitors. [Display omitted] • Three novel dihydroxyl ionic liquids (DHILs) were synthesized. • DHILs facilitated the cementation of clay dispersion to enhance its thixotropy. • Both dihydroxyl and long alkyl chains highly improved the inhibition performance. • The proposed inhibition mechanism was verified via molecular dynamics simulation. [ABSTRACT FROM AUTHOR]

Ionic liquids (ILs) have been introduced as novel high-performance shale inhibitors. The inhibition performance and mechanism of the cation groups in ILs have been widely investigated, whereas the effects of the anionic groups in ILs on the inhibitory capacity have rarely been reported. In this work, a series of fatty acid-based ionic liquids (FAILs) with different anionic groups, methyltrioctylammonium octanoate ([N 8881 ][C 8:0 ]), methyltrioctylammonium laurate ([N 8881 ][C 12:0 ]), and methyltrioctylammonium palmitate ([N 8881 ][C 16:0 ]), were synthesized to evaluate their inhibition ability via the sodium bentonite (Na-Bent) immersion test, the linear swelling test, and the shale hot-rolling recovery test. Compared with the traditional inhibitor KCl (2 wt%), FAIL [N 8881 ][C 8:0 ] showed greater inhibition performance at a much lower concentration (0.1 wt%). The inhibition mechanism of FAILs was further analysed by Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), zeta potential measurements, and contact angle measurements. It was speculated that the best inhibition ability and thermal stability of [N 8881 ][C 8:0 ] should be attributed to the intensive interaction and the size-matching effect between cationic and anionic groups. The present study provided novel insight into the research and development of high-efficiency shale inhibitors. [Display omitted] • FAILs exhibit great shale inhibition performances and thermal stability. • FAILs inhibit the clay swelling by electrostatic adsorption and hydrophobic shield. • The multiple cation/anion interaction in FAILs generate intensive adsorption layer. • The anionic group with optimal size-matching effect enhances the inhibition property. [ABSTRACT FROM AUTHOR]

Ionic liquids are regarded as the promising and efficient additives to use in various aspects of petroleum industry, especially in chemical EOR. In this investigation, three novel fatty acid ionic liquids (FAILs), methyltrioctylammonium octanoate ([N 8881 ][C 8:0 ]), methyltrioctylammonium laurate ([N 8881 ][C 12:0 ]) and methyltrioctylammonium palmitate ([N 8881 ][C 16:0 ]), were selected and evaluated for their performances in terms of surface/interfacial activity, temperature and salt resistances. The three FAILs could cause remarkable reduction of surface tension to ~30mN/m in their aqueous solutions, and the [N 8881 ][C 8:0 ] with the shortest anionic alkane chain exhibited the greatest surface activity among three FAILs. Then the size-match effect and intermolecular interaction were employed to explain the abnormal variations, which were confirmed by the control experiments using mixed surfactants and the molecular dynamics simulation. It was found that the binding energy in [N 8881 ][C 8:0 ] (−28.961 kcal/mol) was larger than that in [N 8881 ][C 16:0 ] (−22.942 kcal/mol), which should be responsible for their different surface activity. Moreover, the crude oil/water interfacial tension (IFT) could be decreased to the much level (4.9 ×10−3 mN/m and 1.7 × 10−2 mN/m) even at high-temperature conditions (80 °C) and at high-salinity conditions (100,000 mg/L), indicating the FAILs might be the ideal candidate for the EOR used surfactants with great temperature and salt tolerances. Meanwhile, the variations of IFT results further verified our proposed mechanism. [Display omitted] • FAILs exhibited the abnormal variation of surface/interfacial activity. • Both size-match and intermolecular interaction decide interfacial activity of FAILs. • Molecular simulation provides visual insight to the interfacial arrangement of FAILs. • FAILs possesses remarkable IFT reduction ability to ultralow level. • Great salt/temperature resistances of FAILs imply the promising application in EOR. [ABSTRACT FROM AUTHOR]

Graphene sheets can be effectively dispersed by a novel ionic liquid-based polyether, poly(1-glycidyl-3-methylimidazolium chloride) (PGMIC), in aqueous solution. The reduction of graphene oxide to graphene is confirmed by UV-Vis and Raman spectrum in aqueous solution of PGMIC. TEM image showed that the stable and uniform dispersion of graphene sheets were obtained. Both the TGA and AFM analysis indicated that the graphene sheet was covered by PGMIC. FTIR spectra demonstrated that n-π, cation-π interactions and electrostatic repulsions played important roles in the dispersion of graphene sheets. [ABSTRACT FROM AUTHOR]

It is an urgent subject to search high-performance shale inhibitors used in water-based drilling fluids for drilling safety. In the present work, two imidazolium-based ionic liquids (ILs), 1-hexyl −3-methylimidazolium bromide (BMH) and its corresponding gemini type, 1,2-bis(3-hexylimidazolium-1-yl) ethane bromide (HMH), were introduced as promising shale inhibitors. The inhibition performances were assessed and compared with the conventional inhibitors potassium chloride and polyether diamine (PDA) via the inhibition evaluation tests including sodium bentonite (Na-bent) pellets immersing tests, linear swelling tests and shale hot-rolling recovery tests. Both ILs inhibitors, especially HMH, shown terrific inhibition performance with lower dosages and maintained high-performance at temperature up to 160 °C. The inhibition mechanism was analyzed by FTIR, X-ray diffraction (XRD), Zeta potential tests, particle size distribution measurement, contact angle measurement and surface tension measurement. The results demonstrated both BMH and HMH effectively inhibit the shale hydration and swelling. HMH, with two positively charged headgroups and two hydrophobic tails, was better than BMH in entering the interlayer space of clay, reducing Zeta potential, forming hydrophobic shield and reducing the surface tension, which was responsible for its superior inhibition performance. • A gemini ionic liquid HMH was innovatively introduced as shale inhibitor. • HMH with two electropositive headgroups enhanced the electrostatic interaction. • HMH with two hydrophobic tails strengthened the hydrophobic shield on clay surface. • HMH showed higher surface activity to reduce surface tension. • HMH presented superior inhibition performance than the traditional ionic liquid BMH. [ABSTRACT FROM AUTHOR]

Ionic liquid-type gemini surfactants have the advantages of both a gemini surfactant and a surface active ionic liquid and have been widely applied in multiple fields. A series of ionic liquid-type gemini imidazolium surfactants with a four-methylene spacer group (CnD, n = 8, 10, 12) was introduced for chemical enhanced oil recovery. The CnD had great effects on the interfacial tension (IFT) between water and a model oil (toluene and n-decane, v:v = 1:1), which appears to be closely related to the hydrocarbon chain length. Interestingly, the addition of NaCl caused abnormal variations in the IFT values. Based on the phase behaviour of the surfactants in solution, we proposed a mechanism to explain the relationship between the salt effects and the surfactant concentration, which was verified by measuring the IFT values between the surfactant solutions and a homologous series of alkanes with different alkane carbon numbers. The temperature effects were also evaluated to further explore the effects of the CnD molecular structures on the IFT. [ABSTRACT FROM AUTHOR]

In this investigation, a novel anionic- halogen-free ionic liquid (IL), 1-butyl-3-methylimidazolium dodecyl sulfate ([C 4 mim][C 12 SO 4 ]), was synthesized and examined for possible application in the chemical enhanced oil recovery (EOR) processes. In this way, the effects of [C 4 mim][C 12 SO 4 ] and NaCl concentrations, temperature and model oil type (aliphatic and aromatic hydrocarbons) on interfacial tensions (IFTs) between [C 4 mim][C 12 SO 4 ] solutions and model oils were systematically investigated. It is surprisingly revealed that the novel SAIL [C 4 mim][C 12 SO 4 ] is highly effective in reducing the IFT of aromatic hydrocarbon/water system, and ultra-low IFT can be achieved in the presence of salinity at higher temperature. Moreover, the interaction energies between [C 4 mim][C 12 SO 4 ] and different model oil molecules were calculated using molecular mechanics, which could further interpret the reasons of ultra-low IFT. [ABSTRACT FROM AUTHOR]

Gold nanorods have been recognized as a good candidate for developing novel nanomaterials due to their exceptional optical properties. However, their assemblies, especially with the assisted ionic liquid, have not been well characterized. In this paper, we report the self-assembly of gold nanorods using thiol-functionalized ionic liquid (1-methyl-3-(2′-mercaptoacetoxyethyl) imidazolium bromine) (TFIL). We found that gold nanorods can self-assemble via two different ways: From end-to-end to side-by-side with the increase of TFIL concentration. The shift of the absorption peak in UV–vis spectrum indicates the change of the assembly fashion. We propose that the π–π stacking interactions between the imidazole rings of TFIL molecules play the most important role in regulating the assembly process. The energy calculation further demonstrated that the face–face stacked orientation was the most stable geometry at high TFIL concentration, which supports the proposed mechanism. These gold nanorod assemblies were shown to yield the large SERS enhancements for Rhodamine 6G. [ABSTRACT FROM AUTHOR]