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[Display omitted] • Synthesis of phosphorus free organic molybdenum additive. • Phosphorus free organic molybdenum additive greatly reduces wear volume. • The organic molybdenum additive has excellent anti-friction and anti-wear. • The lubrication mechanism of organic molybdenum additive was discussed. A phosphorus-free triazine-based organic molybdenum compound (DCDM) was designed and synthesized by using the click chemistry approach, and its friction-reducing and anti-wear properties were evaluated in PAO10 base oil. The results indicated that DCDM exhibited excellent tribological performance, with a reduction of approximately 35% in friction coefficient and about 46% in wear scar diameter, due to the synergy effect between Mo and S. Surface analysis by EDS and XPS revealed the formation of MoO 3 , Fe 2 (SO 4) 3 , FeS, and MoS 2 in the friction film. And it was furhter confirmed that the presence of MoS 2 in the friction film contributed most significantly to the enhancement of the friction-reducing and anti-wear properties of the developed triazine-based organic molybdenum compound in PAO10 base oil. [ABSTRACT FROM AUTHOR]

• A significant dispersion of the charging current characteristics of nanofluids with magnetic nanoparticles is observed. • At lower electric field intensities, the increasing fullerene concentration of the hybrid nanofluids reduces the charging currents up to a charging time of 200 s. • Magnetic nanofluid shows the highest values of conductivity currents. • At higher electric field intensities in the low-frequency spectrum, the relaxation peaks decrease when the concentration of fullerene in hybrid nanofluids increases. • Compared to lower electric field intensities, at the value of 333.3 kV/m, several polarization processes are captured in the entire frequency spectrum. Improving the dielectric properties of insulating liquids belongs to the modern motivation to optimize the operation of high-voltage devices. Hybrid nanofluids can provide the mentioned improvement, and thus, it is necessary to reveal their hidden potential. This study investigates hybrid nanofluids with different concentrations of magnetite and fullerene nanoparticles, a separate fullerene and magnetic nanofluid, and a base carrier fluid based on gas-to-liquid technology. The investigated samples are subjected to dielectric relaxation spectroscopy analysis at three applied electric field intensities in the time, distribution, and frequency domain. The lack of information about the studied parameters of the mentioned nanofluids is another reason for our experimental measurements. A significant dispersion of the charging current characteristics of nanofluids with magnetic nanoparticles is observed. At lower electric field intensities, the increasing fullerene concentration of the hybrid nanofluids reduces the charging currents up to a charging time of 200 s. Magnetic nanofluid shows the highest values of conductivity currents. Experiments show that the suspension of fullerene in the base oil causes a higher charging current and a more pronounced relaxation response than pure base oil. Significant relaxation information in the low-frequency band is detected from the distribution spectra. At higher electric field intensities in the low-frequency spectrum, the relaxation peaks decrease when the concentration of fullerene in hybrid nanofluids increases. The distribution area shows the effect of higher polarizability of magnetite nanoparticles. Compared to lower electric field intensities, at the value of 333.3 kV/m, several polarization processes are captured in the entire frequency spectrum. The frequency-dependent complex permittivity confirms the findings from the time and distribution domains. Comparing the distribution domain with the frequency domain shows higher sensitivity and accuracy in capturing relaxation processes in the distribution domain. [ABSTRACT FROM AUTHOR]

[Display omitted] • Boundaryand elastohydrodynamic lubrication models with additives under sinusoidal load were studied by NEMD. • The additive's solidification degree reflects the interlacing strength, thus relative motion less occurs in the BL regime. • The liquefaction degree and the velocity difference of base oil and additive regions, affect friction in the EHL regime. The evolution of lubricating oil containing additives under dynamic conditions is very significant, since its oil film structure, velocity distribution, and adsorption characteristic have an obvious impact on friction and wear. In this work, a boundary lubrication (BL) and elastohydrodynamic lubrication (EHL) models under sinusoidal load were carried out by nonequilibrium molecular dynamics (NEMD), using iron oxide as the substrate, hexadecane, and stearic acid molecules as lubricants. It was discovered that the friction in the BL regime is positively correlated with the degree of additive's solidification. The greater the solidification degree of additive layers, the less the interlacing between them, making the relative motion between them easier and reducing compression oscillation within them, thus diminishing friction in the BL regime. The degree of liquefaction of base oil and additive regions, as well as the velocity difference within their interlacing zones, are connected to the friction force in the EHL regime. At high frequencies as well as large amplitudes, the oil film has a very high degree of liquefaction, which facilitates internal shear in it, and there is essentially no relative motion between the base oil and additives, resulting in low friction. [ABSTRACT FROM AUTHOR]

[Display omitted] • High-performance lubricants: Polyisobutylenes (PIBs) and polybutenes (PBs) meet extreme industrial conditions. • The innovative Boehmite-supported ionic liquids (B-ILs) enhance Raffinate-1 polymerization. • Improved process since B-ILs reduce AlCl 3 usage, boosting safety and cutting costs. • Characterization success including FTIR, TGA, SEM, and XRD confirm ILs synthesis and stability. • PBs show high kinematic viscosity and VI, effective across temperatures. Lubricants, composed of a base oil and various additives, reduce friction and abrasion between moving surfaces. High-performance lubricants, especially in the automotive and space industries, have driven advancements in synthetic oils like polyalphaolefins (PAOs), known for their high viscosity index and stability. Low molecular weight polyisobutylenes (PIBs) are used in multiple applications, including as viscosity improvers. PIBs are produced via cationic polymerization of isobutylene using Lewis acid initiators and co-initiators, often conducted at low temperatures with harmful substances like BF 3. Efforts are being made to develop more eco-friendly processes, such as using AlCl 3 and ionic liquids (ILs). In this research, boehmite-supported dendritic ILs (Gen1 and Gen2) were synthesized and tested as co-initiators in Raffinate-1 polymerization. The ILs improved the stability of the catalytic system, allowing for reduced AlCl 3 usage, and produced PIBs with desirable molecular weight and viscosity characteristics. Density Functional Theory calculations unveiled the importance of the interaction of AlCl 3 with the ionic liquids. [ABSTRACT FROM AUTHOR]

[Display omitted] • TBPB and TOPB ILs as demulsifiers are used in breaking water in crude oil emulsions. • Four models for the prediction of demulsification efficiencies are created by RSM. • Temperature, pH, water content, concentration, and settling time are optimized. • TBPB and TOPB show acceptable results for light and medium oil emulsion separation. • Crude oil emulsions are completely broken by TOPB at the optimal conditions. In the present study, the performance of two ionic liquids namely Tetrabutylphosphonium bromide (TBPB) and Tetraoctylphosphonium bromide (TOPB) as the demulsifying compounds are investigated in the demulsification operation of water in light and medium crude oil emulsions for the first time. The response surface methodology (RSM) is employed to evaluate the impact of temperature, pH, water content, demulsifier concentration, and settling time on the demulsification efficiencies of studied demulsifiers. In order to design the requisite experiments and optimize the effective factors on the water removal efficiency, the central composite design (CCD) is applied. To determine the optimal conditions of input parameters, four exact models are created by utilizing the responses of 184 experiments to predict the demulsification efficiencies of two demulsifiers for two types of crude oils based on statistical tests of different models using the analysis of variance (ANOVA). High R2 coefficient values imply that the developed models could reproduce the experimental results of the studied demulsifiers appropriately. At the optimal conditions, the water in light and medium crude oil emulsions are completely broken in the samples containing TOPB. Moreover, TBPB agent presents high and acceptable demulsification efficiencies for both types of crude oils at the optimal values of process parameters i.e. 98.078% and 96.025% for light and medium crude oil emulsions, respectively. The superior demulsification performance of TOPB with respect to TBPB can be ascribed to the longer alkyl chain length of TOPB. [ABSTRACT FROM AUTHOR]

• This comprehensive review paper explores the evolution of dielectric fluids for transformers, emphasizing environmentally friendly alternatives and advancements in nanofluids. The adoption of ester-based dielectric liquids, both synthetic and natural, is examined, highlighting their fire safety, biodegradability, and environmental sustainability. • Studying how nanofluids age is crucial to understand how well they perform in real and extended operating situations for transformers. Yet, because of stability concerns, the ageing process used for regular insulating oils can't be applied to nanofluids. • Enhancing the heat and electricity features of the liquid can bring about significant transformations in the design of transformers. Additionally, the mismatch between nanofluids and the current transformer materials necessitates the exploration of new materials for the secure and effective functioning of transformers. Investigating the necessary design adjustments for transformers filled with nanofluids represents another area that requires thorough examination. • In contrast to using just one kind of tiny particle and a basic fluid, nanofluids that involve multiple particles and a blend of base fluids employ various types of nanoparticles mixed in different proportions with the base oil. Each type of particle has the potential to boost various properties, both in the nanoparticles themselves and in the base oil. The contribution of this article is to update the reader on the latest developments of transformer insulating oils in ensuring the reliability of power systems. Commencing with the prevalent use of mineral oil (MO), our exploration extends to alternative solutions, including esters. The scrutiny of esters involves a particular emphasis on natural variants highlighting their potential as eco-friendly substitutes for conventional insulating oils. A significant aspect of this work entails the incorporation of different nanoparticles (NPs) into vegetable insulating oils, forming nanofluids, which emerge as a promising avenue for enhancing insulating properties. The paper systematically categorizes nanoparticles based on conductivity and thoroughly examines nanofluid synthesis methods. Stability assessment techniques, encompassing sedimentation capturing, zeta potential analysis, and spectral analysis, are discussed alongside strategies for stability enhancement, including surfactant addition, surface modification, ultrasonic agitation, and pH control. Environmental considerations, covering biodegradability, recyclability, and fire protection, are scrutinized for both mineral and vegetable oils. [ABSTRACT FROM AUTHOR]

[Display omitted] • A new dimercaptobenzothiadiazole consists of four and five sulfur atoms. • Excellent EP and AW performance of dimercaptobenzothiadiazole additives. • The dimercaptobenzothiadiazole additives are non-corrosive and ashless. • Sulfonitrided tribofilm serve as an excellent boundary lubrication layer and surface protection. Lubricant additives are essential to protect mechanical devices. Although sulfur (S)-based dialkylpentasulfide (RC2540) exhibits acceptable extreme pressure (EP) performance, a high amount of S causes severe corrosion and poorer anti-wear (AW) performance. Herein, dimercaptobenzothiadiazole-based additives (DMTDs) consist of four and five S atoms, namely 2-(benzyldisulfanyl)-5-(benzylsulfanyl)-1,3,4-thiadiazole (4SBZ), 2-(octyldisulfanyl)-5-(octylsulfanyl)-1,3,4-thiadiazole (4SC8), 2,5-bis(benzyldisulfanyl)-1,3,4-thiadiazole (5SBZ), and 2,5-bis(octyldisulfanyl)-1,3,4-thiadiazole (5SC8) were synthesized. The synthesized DMTDs are non-corrosive (Grade 1a-1b) compared to RC2540 (Grade 4c). The 10 wt% 5SBZ demonstrated exceptional EP and AW performance than RC2540. The 10 wt% 5SBZ has improved weld load and reduced wear scar area by 5.0 folds and 94.1% compared to naphthenic base oil. The exceptional tribological properties of 5SBZ are attributed to the strong non-covalent interaction between the benzene ring and metal surfaces, high S content, and synergistic effect between S and N. Alternatively, the DMTDs exhibit better AW performance compared to RC2540. The XPS depth profiling demonstrated the formation of sulfonitrided tribofilm after lubrication with synthesized DMTDs. This tribofilm contributed to an excellent boundary lubrication layer for wear protection. The lubrication mechanism was discussed and proposed. This work provides promising DMTDs as EP and AW additives for industrial applications. [ABSTRACT FROM AUTHOR]

• RSM predicts MoS 2 -hBN nanolubricant viscosity across temperature and shear rates, validated with experimental tests. • Optimal conditions yield 12.87 mPa·s viscosity with 0.05 wt% MoS 2 -hBN, 100 °C, and 200 s−1 shear rate. • MoS 2 -hBN nanolubricant enhances oxidation stability, reduces friction, and minimizes wear, improving engine performance. • MoS 2 -hBN nanolubricant exhibits enhanced thermal stability, tribological properties, and heat transfer efficiency. • Potential for high-temperature applications, enhancing durability in diverse industrial contexts. This study utilizes Design of Experiment (DOE) to optimize the viscosity of MoS 2 -hBN nanolubricants, synthesized using a microwave synthesis platform that significantly reduces synthesis time and energy consumption compared to other methods. The investigation focuses on viscosity and aging characteristics, aiming to understand the relationship between nanolubricant viscosity and key factors: nanoparticle concentration, temperature, and shear rate. The study shows that the optimal concentration of MoS 2 -hBN nanoparticles is 0.05 wt%. At this concentration, when subjected to a shear rate of 200 (1/s) and a temperature of 100°C, the highest viscosity recorded is 12.87 mPa·s. In contrast, at 40°C and a shear rate of 50 (1/s), the lowest viscosity measured is 113.42 mPa·s. Experimental validation confirms the accuracy of the model predictions. The study also examines MoS 2 -hBN nanolubricant aging behavior under constant high-temperature conditions (100 °C for 120 h), providing insights into its thermal stability, tribological performance, oxidation resistance, and thermal conductivity properties. Compared to SAE20W40 base oil, the nanolubricant reduces friction and wear, forming a protective boundary film to mitigate surface damage. It exhibits enhanced oxidation stability, acting as a free radical scavenger, and improved thermal conductivity due to increased heat transfer efficiency facilitated by nanoparticles. These findings highlight the potential of MoS 2 -hBN nanolubricant for high-temperature applications, contributing to enhanced engine performance and durability. [ABSTRACT FROM AUTHOR]

• An environmentally friendly and inexpensive chitosan + geopolymers-oil shale composite was proposed. • Characterized by different methods have shown an interaction between chitosan and geopolymers. • The composite demonstrated good performance for the management of U(VI) wastewater. • A theoretical study was studied to know the adsorption mechanism. This study introduces an innovative geopolymer composite (Ch@GPol), synthesized from oil shale and chitosan (Ch), tailored to improve Uranium (VI) adsorption. Experimental and theoretical methods were applied to explore the distinct characteristics and potential applications of the composite. Various techniques were employed, including X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infrared (FT-IR) spectroscopy, and thermogravimetric analysis (TGA). The interaction between chitosan and the geopolymer was scrutinized through FTIR and XRD analyses, revealing substantial alterations in the composite structure. Adsorption experiments highlighted the exceptional U(VI) removal performance of the composite from aqueous solutions. Comparative to materials in the literature, the Ch@GPol exhibited a notably high adsorption capacity of 0.236 mol kg−1. The maximum adsorption capacity was observed at the natural pH of the uranium(VI) solution. showcasing the composite's versatility. Textural analyses of the Ch@GPol, encompassing surface area and pore size distribution, revealed enhanced porosity and favorable adsorption characteristics. The determination of the point of zero charge (pHPZC) provided insights into surface charge distribution, emphasizing the composite's applicability across a broad pH range. Kinetic studies demonstrated rapid adsorption kinetics, with the pseudo-second-order model best describing the adsorption process. Density Functional Theory (DFT) analysis offered structural insights into the interaction between the composite and Uranium (VI), confirming robust binding capabilities. [ABSTRACT FROM AUTHOR]

• Sesame oil was used as a natural substance for the synthesis of a new anionic surfactant. • Thermal stability and characterization of the surfactant were shown by TGA, FTIR, and 1H NMR analysis. • The crude oil–water IFT was achieved to a low value by the surfactant and the rock wettability was shifted to water-wet. • The surfactant was able to generate a stable foam and emulsion. • A 16.18% increase in oil recovery was achieved by optimal fluid flooding. This study is centered on creating an anionic surfactant using edible sesame oil for enhanced oil recovery (EOR) objects. The surfactant was synthesized under esterification and sulfonation processes. Characterization analyses were performed to describe the surfactant and evaluate its temperature stability. Related experiments were conducted to investigate phase behavior, surface activity, and EOR implications of the surfactant. A chemical flooding experiment was carried out. This involved injecting the surfactant along with the appropriate levels of salinity and alkalinity, into a carbonate plug. Additionally, the ability of the surfactant to generate and maintain foam and emulsion was examined. The surface tension values were reduced from 64 to 33.07 mN/m, and the interfacial tension (IFT) values dropped from 21 to 0.81 mN/m. Through these experiments, the critical micelle concentration (CMC) of the surfactant was determined to be 800 ppm. Upon reaching the CMC, the IFT further decreased to 0.38 and 0.14 mN/m at optimal salinity and alkalinity levels respectively. The previously hydrophobic carbonate surface underwent significant improvement in wettability, transitioning to hydrophilic behavior. This shift was evident as the contact angle decreased from 130.2° to 58.8° within a brief 60-minute equilibration period, representing a suitable wettability state for EOR. The surfactant exhibited an emulsion and foam stability period lasting 35 days. Additionally, its ability to function effectively in the presence of sodium chloride (NaCl) ions was verified with compatibility demonstrated at salinity levels below 100000 ppm. Ultimately, the flooding outcomes displayed a notable 16.18 % enhancement in oil recovery when employing the optimum fluid. [ABSTRACT FROM AUTHOR]

[Display omitted] • The addition of CaCO 3 and CeF 3 NPs to the base oil results in small decreases in the surface tension. • Friction coefficients for all the nanolubricants are smaller than the obtained for PAO8 base oil. • Produced wear for nanolubricants is lower than for the PAO8 with a maximum improvement of 28 % in WSD (0.15 wt% CaCO 3). • Surface repairing, tribofilm formation and ball bearing could be suggested as tribological mechanisms. The rise of the electric vehicles as a more sustainable transport alternative makes it necessary to study new transmission fluids that adapt to their needs and improve their efficiency. The thermophysical properties (contact angle, surface tension and rheology) and tribological properties (friction and wear) of potential PAO8 transmission nanofluids using CaCO 3 and CeF 3 nanoparticles as additives are evaluated at mass concentrations of 0.05, 0.10, 0.15 and 0.20 wt%. Low contact angle and surface tension values are obtained, indicating good wettability. When the nanoparticles are used as PAO8 additives, small reductions in surface tension are achieved, but no differences in contact angle are observed. All nanolubricants and base oil exhibit Newtonian behavior. Concerning the tribological behavior, reductions in the friction coefficient are achieved for both types of nanoparticles, with the largest reductions comparing to PAO8 base oil being 13 % and 10 % for nanolubricants containing 0.05 wt% CaCO 3 and 0.10 wt% CeF 3 nanoparticles (NPs), respectively. In terms of antiwear performance, maximum reductions are obtained for the CaCO 3 nanolubricant of 28 % (0.15 wt%), 41 % (0.10 wt%) and 59 % (0.15 wt%) and for the CeF 3 nanolubricant of 19 % (0.20 wt%), 53 % (0.10 wt%) and 58 % (0.20 wt%) for the parameters of diameter, depth, and area of the worn track, respectively. Through Raman microscopy, the tribological mechanisms of tribofilm formation, repairing, and rolling can be proposed. A discontinuous tribofilm formed by the CaCO 3 and CeF 3 nanoparticles reduces the contact area between the two surfaces protecting them. [ABSTRACT FROM AUTHOR]

[Display omitted] • The presence of calcite mineral in dolomites was found to increase the wettability alteration. • Carbonate rock containing dolomite showed the maximum decrease in contact angle for MgCl 2 low salinity brines. • Carbonate rock containing calcite showed the maximum decrease in contact angle for CaSO 4 low salinity brines. • The type of mineral composition and brine affected the extent of wettability alteration in carbonate rocks. While many low salinity studies have been conducted on chalks, calcite minerals and sandstone rocks, few research articles have explored the same for applications in dolomite rocks. To explore the effect of mineralogy, a comparative study on the wettability alteration in the presence of low salinity brines for 2 carbonate rocks of varying composition was studied. The contact-angle experiments were performed for two carbonate samples. One carbonate sample was composed of ∼100 % dolomite mineral whereas the other carbonate rock sample was composed of both dolomite and calcite mineral (5 % calcite and 95 % dolomite). The ionic solutions were composed of NaCl, MgCl 2 , CaCl 2 and CaSO 4 single salt solutions of concentration (500 ppm to 5000 ppm). The contact angle reduction was observed in the following order CaSO 4 > MgCl 2 > CaCl 2 > NaCl for the carbonate sample containing calcite and dolomite minerals and the maximum reduction in contact angle for the carbonate sample containing dolomite and calcite minerals was observed for CaSO 4 brines was 26.13 % for 1000 ppm concentration. The contact angle reduction observed for the carbonate sample containing dolomite mineral was found to be in the following order MgCl 2 > CaCl 2 > CaSO 4 > NaCl and the maximum reduction in contact angle was observed for MgCl 2 brines was 24.58 % for 3000 ppm concentration. The wettability alteration observed in the carbonate sample containing dolomite mineral was less as compared to the carbonate sample containing calcite and dolomite mineral. In the presence of MgCl 2 brines, the pH of the brines dominates the mineral dissolution, thereby improving or reducing the extent of wettability alteration. However, the complete wettability reversal has not been observed in this study. An increase in temperature (from 70 to 90 °C) was found to be favourable for wettability alteration while the presence of calcites, along with dolomites has the potential to further improve oil recovery. [ABSTRACT FROM AUTHOR]

[Display omitted] • Ti 3 C 2 T z used as an additive to enhance fluidic properties and tribological performance. • Non-Einstein viscosity drop was observed for Ti 3 C 2 T z MXene-based nanofluids. • The addition of Ti 3 C 2 T z improved thermal conductivity by 16 % and 23 % in silicone and PAO oils, respectively. Nanoparticle additives are known to enhance a range of fluidic properties, including thermal conductivity, heat capacity, and viscosity. Ti 3 C 2 T z nanosheets exhibit high thermal conductivity, electrical conductivity, and mechanical strength, making them promising candidates as lubricant additives. In this work, we evaluate the performance of Ti 3 C 2 T z as an additive to enhance the heat transfer, rheological properties, and tribological performance of silicone and Polyalphaolefin (PAO) oils. The acid-etched Ti 3 C 2 T z nanosheets were synthesized and characterized by SEM, XRD, and XPS to confirm etching. The nanofluids were produced by dispersing the Ti 3 C 2 T z nanosheets in silicone and PAO oils at different loadings. Experimental results showed that adding Ti 3 C 2 T z improved thermal conductivity by 16 % and 23 % in silicone and PAO oils, respectively. The rheological data revealed that adding Ti 3 C 2 T z nanosheets reduced the viscosity by 12.3 % (at 0.09 wt%) and 18.1 % (0.04 wt%) in silicone and PAO oil, respectively. This non-Einstein viscosity reduction can be attributed to the disruption of intermolecular bonding of base oil molecule. The addition of Ti 3 C 2 T z reduced the friction by 23 % (0.09 wt%) and 65 % (0.04 wt%) in silicone and PAO oils, respectively. The improved properties and reduced fluidic drag in viscosity and friction lead to potential applications in (electrical) vehicles that will be helpful in attaining improved fuel economy. [ABSTRACT FROM AUTHOR]

[Display omitted] • Imidazolium-based ionic liquids (ILs) were encapsulated in methacrylate polymer microcapsules. • Polymer-encapsulated ILs were dispersed in non-polar oils at concentration that exceeds their solubility limit. • Polymer-encapsulated ILs led to a reduction of friction in steel/steel sliding contacts. • Encapsulated imidazolium-based IL does not tribochemically react at steel surfaces. While ionic liquids (ILs) have attracted much attention as potential next-generation lubricant additives, their implementation in oil formulations has been hindered by their limited solubility in hydrocarbon fluids and corrosivity. Here, we encapsulate an oil-insoluble IL that has been studied in lubrication science, namely 1-hexyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide ([HMIM][TFSI]), within poly(ethylene glycol dimethacrylate-buytl methacrylate copolymer) (poly(EGDM-c-BMA)) microshells using a mini-emulsion polymerization process. The synthesized poly(EGDM-c-BMA)-encapsulated [HMIM][TFSI] microparticles are shown to be dispersible in a non-polar, synthetic oil (i.e. , poly-α-olefin). Tribological experiments indicated that the microcapsules act as an additive reservoir that reduces friction by releasing the encapsulated IL at the sliding interface following the mechanical rupture of the polymer shell. X-ray photoelectron spectroscopy (XPS) measurements provided evidence that [HMIM][TFSI] does not tribochemically react on steel surfaces to create a reaction layer, thus suggesting that this IL reduces friction by generating a solid-like, layered structure upon nanoconfinement at sliding asperities, as proposed by previous nanoscale studies. The results of this work do not only provide new insights into the lubrication mechanism of ILs when used as additives in base oils in general, but also establish a new, broadly-applicable framework based on polymer encapsulation for utilizing ILs or other compounds with limited solubility as additives for oil formulations. [ABSTRACT FROM AUTHOR]

[Display omitted] • Poly(tannic acid) functionalized onion-like carbon nanoparticles (P(TA-TAEA)@OLC) were prepared successfully. • The as-prepared DDP@OLC nanospheres exhibit excellent friction reduction and anti-wear abilities as base oil additive. • The good tribological performance is attributable to the formation of carbon protective film from OLC nanoparticles. Spheroidal onion-like carbon (OLC) nanoparticles exhibit heliocentric graphitic layers are known to possess excellent lubricating properties. Herein, tannic acid (TA) was assembled in-situ onto the onion-like carbon material with Tris (2-aminoethyl) amine (TAEA) to form poly(tannic acid)-functionalized onion-like carbon nanoparticles (P(TA-TAEA)@OLC) via Schiff-base reaction and/or Michael addition. Subsequently, the commercial lubricating additive dialkyl dithiophosphate (DDP) was introduced via Michael addition to bond with the poly(tannic acid) of P(TA-TAEA)@OLC nanoparticles in Tris aqueous solution, to obtain DDP-functionalized onion-like carbon (DDP@OLC) nanoparticles. The as-obtained DDP@OLC nanospheres in the role of lubricating additives demonstrated remarkable friction reduction and wear resistance. With addition of 1 wt % DDP@OLC nanoparticles, the coefficient of friction reduced from 0.17 to 0.10, while the corresponding wear volume loss decreased by 96 %, and the loading capacity reached 600 N from 100 N. The outstanding tribological performance of these as-obtained nanoparticles can be attributable to the formation of a graphitic layer exfoliated from OLC nanoparticles under a high load, and the protective film derived from tribochemical reactions via N, P and S elements of DDP@OLC. Meanwhile, the DDP@OLC nanoparticles can also act as spacers and ball bearings between sliding surfaces, facilitating the enhancement of anti-wear and friction reduction properties. [ABSTRACT FROM AUTHOR]

[Display omitted] • The solubility parameter profiles were used to characterize the interfacial regions. • Solubility parameter differences allow for predicting the affinity by the interface. • The affinity by the interface is controlled by electrostatic and vdW contributions. Crude oils are formed of asphaltenes that are species soluble in certain solvents such as toluene. The distribution of asphaltene models and their mixtures in water/n–heptane and water/toluene systems were explored with MD simulations. A1 and A2 asphaltene models were used for the exploration of the affinity of these compounds by the water/oil interfaces. For this, a novel concept called solubility parameter profiles was used to characterize the polarity of the regions present in water/n–heptane and water/toluene systems. Molecules of asphaltene models, n–heptane, and toluene were described with the GROMOS53A6 force field and CHELPG atomic charges, and water molecules with the SPC model. The prediction of the affinity of A1 and A2 asphaltene models at interfaces was determined using the total solubility parameter differences calculated between these species and solvent molecules. Calculated solubility parameters show a good correlation with experimental values. Total solubility parameter differences equal to Δ δ total = 3.76 MPa 0.5 and Δ δ total = 0.36 MPa 0.5 at the water/n–heptane interface suggest that asphaltene models have a good affinity by the water/n–heptane interface in comparison with the water/toluene interface whose values were Δ δ total = 5.82 MPa 0.5 and Δ δ total = 9.94 MPa 0.5 for A1 and A2 asphaltene models, respectively. It was demonstrated that the affinity of asphaltenes by a specific region of the immiscible system is controlled by the electrostatic and dispersive contributions associated with the solubility parameter profiles. [ABSTRACT FROM AUTHOR]

[Display omitted] • Oleic acid coated TiO 2 nanoparticles were synthetized. • PAO8 + 0.35 wt% TiO 2 -OA nanolubricant was the optimal nanolubricant. • Maximum friction and wear reductions of 30 and 73% were obtained, respectively. • Tribofilm, mending and polishing mechanisms occur due to nanoadditives. This work presents the antifriction and antiwear properties of TiO 2 nanoparticles coated with oleic acid, TiO 2 -OA, as additives of a low viscosity polyalphaolefin base oil, PAO8. To find the optimal concentration of nanoadditives that minimize friction and wear, four PAO8 based nanodispersions were formulated: PAO8 + 0.10 wt% TiO 2 -OA, PAO8 + 0.25 wt% TiO 2 -OA, PAO8 + 0.35 wt% TiO 2 -OA and PAO8 + 0.50 wt% TiO 2 -OA. Tribological experiments were performed under pure sliding and rolling-sliding conditions at 120 °C, with the four formulated nanolubricants and with PAO8 base oil. All the nanolubricants showed lower friction coefficients than that obtained with the PAO8 base oil, reaching maximum reductions for the 0.35 wt% TiO 2 -OA nanolubricant, for both types of test conditions. The tribological specimens tested under pure sliding conditions with the nanolubricants showed fewer wear than those tested with PAO8, finding the highest wear decreases also with the PAO8 + 0.35 wt% TiO 2 -OA nanolubricant, being 26 %, 65 % and 73 %, in wear track width, depth and area, in that order. Through Raman microscopy and roughness study of the worn samples, it can be inferred that tribofilm, mending and polishing mechanisms occur. Moreover, the thermal conductivity of the optimal nanolubricant (0.35 wt%) was measured at 20, 30, 40 and 50 °C. [ABSTRACT FROM AUTHOR]

• A new IL surfactant is introduced for EOR purposes. • The proposed IL surfactant can tolerate harsh conditions of salinity. • 50,000 ppm is an optimal salinity for the synthesized IL surfactant. • The oil–water IFT is reduced by 95.9% at CMC. • Both IFT reduction and wettability alteration occur upon addition of the surfactant. This study is intended to synthesize and assess a new pyridinium-based Ionic Liquid (IL) surfactant, 1-octadecyl-pyridinium bromide, in terms of crude oil–water Interfacial Tension (IFT) reduction and wettability alteration. The synthesized IL surfactant is firstly characterized through proton Nuclear Magnetic Resonance (1H NMR). Then, the pendant-drop and sessile drop techniques are employed to study crude oil–water IFT and the wettability of carbonate rocks. Based on the IFT results, the synthesized IL has a Critical Micelle Concentration (CMC) of 200 ppm, at which crude oil–water IFT reduces by 95.9 %, from an initial value of 23.7 mN/m to 0.97 mN/m. Increasing the salinity up to 100,000 ppm could not make the synthesized IL less effective than that of free from salinity, as the magnitude of IFT is obtained to be 0.938 mN/m at CMC. Based on the wettability investigation phase, the synthesized IL changes the wettability of carbonate slices from oil-wet to intermediate-wet (140.47°–90.97°). It is also observed that the synthesized IL can tolerate harsh salinity conditions as no appreciable change in the contact angle is noticed after increasing the salinity even up to 150,000 ppm (84.54° at CMC). It should be noted that an optimal salinity of 50,000 ppm is found based on the results of IFT and contact angle measurements. The introduced surfactant is expected to exhibit a significant positive impact on the oil recovery factor while implementing chemical flooding. [ABSTRACT FROM AUTHOR]

[Display omitted] • Four Mn 3 O 4 -G nanolubricants were formulated. • The best friction and wear behaviors were for the 0.075 wt% Mn 3 O 4 -G nanolubricant. • Maximum friction and wear reductions of 4 and 64% were obtained, respectively. • Rolling and tribofilm mechanisms occur due to nanoadditives. This research reports the antifriction and antiwear properties of Mn 3 O 4 -Graphene nanocomposites (Mn 3 O 4 -G) as additives of a paraffinic base oil commonly used in the formulation of electric vehicles transmission oils, G-III base oil. Four G-III base oil nanodispersions have been designed, G-III base oil + 0.025 wt% Mn 3 O 4 -G, G-III base oil + 0.050 wt% Mn 3 O 4 -G, G-III base oil + 0.075 wt% Mn 3 O 4 -G and G-III base oil + 0.100 wt% Mn 3 O 4 -G, to know the optimal concentration of nanoadditive. Tribological experiments were carried out with these nanolubricants and with neat G-III base oil at pure sliding conditions under a working load of 9.43 N. All tested nanolubricants led to similar friction coefficients in comparison to that obtained using G-III base oil. Tribological specimens tested with formulated nanolubricants revealed less wear than that obtained with G-III base oil, obtaining the greatest wear reduction using the G-III base oil + 0.075 wt% Mn 3 O 4 -G nanolubricant, with reductions of 25, 50 and 64% in wear scar diameter, maximum depth and transversal area, respectively. Moreover, by means of confocal Raman microscopy and roughness evaluation of worn tribological specimens, it was concluded that synergetic effect, tribofilm formation and rolling mechanisms happen. [ABSTRACT FROM AUTHOR]

[Display omitted] • Beeswax and Pluronic F127 hydrogel based lavender oil (LO) formulations have been explored as wound healing ointments. • Rheological and spreading studies show that these ointments are suitable for topical applications. • SANS and SAXS studies suggest that solubilized LO remain trapped in the self-assembled structures formed by these systems. • The confined LO fails to exhibit antimicrobial properties but do show wound healing ability from pluronic hydrogel bases. • The studies show that choice of ointment base is important for LO to exhibit antimicrobial and wound healing properties. Since ancient time, Lavender oil (LO) is being used in aromatherapy as antimicrobial, anxiolytic, analgesic and anti-inflammatory agents. More recently it has been observed that its topical application heals various kinds of wounds by expediting epithelialization and neovascularization processes. Its wound healing characteristics with different delivery systems are however, scarcely reported. The aim of the present study was to evaluate how its healing abilities are manifested when it is applied in the form of beeswax-oil and pluronic F127 hydrogel based ointments. The ointments were prepared by solubilizing or dispersing LO in pluronic F127 hydrogel, beeswax-olive oil, and beeswax-coconut oil based bases. Small angle neutron scattering (SANS) and small angle X-ray scattering (SAXS) studies suggest that the prepared ointments are composed of LO solubilized beeswax-oil and F127-water based self- assembled structures. The rheological and spreading properties of the ointments are found to be suitable for topical applications. The ointments do not exhibit any noticeable antimicrobial actions on gram positive and gram negative bacteria presumably due to entrapment of LO within the self-assembled structures formed in them. Studies on efficacies of the ointments on full thickness mice wounds show that healing ability of LO is manifested only from F127 hydrogel in the form of faster epithelialization and neovascularization at the wound site. Such selective manifestation of wound healing efficacies of LO suggests that choice of ointment base is important for effective harnessing of its wound healing abilities. [ABSTRACT FROM AUTHOR]

• Two new families of protic ionic liquids were synthesized, characterized, and studied as additives to a non-polar oil. • The presence of any protic ionic liquid in the non-polar oil reduced friction and wear of steel disk. • The improved lubrication performance is attributed to an oxygen-rich tribolayer on steel surfaces. Advanced additives are crucial to improve the tribological performance of the base lubricants. A series of protic ionic liquids (PILs) derived from linear alkyl-benzenesulfonic acids with different alkyl chain length, and alkanol amines with different basicity were easily synthesized in the laboratory. The molecular structures of the PILs were established through proton magnetic resonance and Fourier transform infrared spectroscopy. Their thermal behavior was evaluated by differential scanning calorimetry and thermogravimetric analysis. The sliding wear and frictional performance of the PILs used as additives to mineral oil were studied by using a reciprocating ball-on-flat tribometer in a steel-steel contact. The solubility and stability of the PILs were also examined and related to their frictional behaviors. The worn steel surfaces were characterized by a non-contact profilometer, scanning electron microscope, energy-dispersive X-ray spectroscope and Raman microscope. The results showed that all PILs improved the lubricity of mineral oil with the concentration of only 1 wt%. The friction-reducing and anti-wear capacities of these PILs as additives were analyzed and discussed from their structures (different cations associated with anion moieties in different alkyl chain length) and the formed tribo-films. [ABSTRACT FROM AUTHOR]

• Interaction between diamino sulfonate and quasi-one component polyoxyethylenated sulfate. • Dependence of micellization behavior for quasi-binary surfactant mixture. • Effect of the composition of mixed micelle. • Mechanism on synergistic effect in quasi-binary mixture. • Thermodynamics of micellization. In order to obtain some information about the mixture of amphoteric surfactants with other surfactants derived from natural products in the presence of additives, the micellization behavior was investigated in the quasi-binary mixture of an amphoteric amino sulfonate, sodium 3-(N -dodecyl ethylenediamino)-2-hydroxypropyl sulfonate (abbr., DAS), and an anionic fatty alcohol polyoxyethylenated sulfate (CPOS) based on coconut oil in water-glycerol solution. Both the conductometric and the tensiometric techniques were performed to measure the process of micellization. On the basis of regular solution theory, the Rubingh's model, the Rodenas' model and the Clint's model were used to calculate the aggregation parameters and thermodynamic parameters. The Rubingh's treatment can effectively obtain the synergistic interaction between two surfactants in the entire range of composition. The Rodenas' treatment, whereas, fails to give the synergistic effect in these solutions enriched in certain surfactant. The synergistic effect in the DAS/CPOS mixture and the nonideal mixing show the dependence on the composition in the mixture. These effects including electrostatic repulsion, steric hindrance, hydrogen bonding, etc., can rationally account for the variation of interaction behavior with the compositions in mixtures. Thermodynamic data also prove these micellization behaviors and indicate that the entropy plays an overwhelming role on the spontaneous micellization. The release of mixing heat is beneficial to the spontaneity. The obtained results will make for the knowledge of the molecular behavior in the quasi-binary mixtures and further the design of surfactant formulations. [ABSTRACT FROM AUTHOR]

• Density scaling of molecular dynamics. • Inflection points in isotherms of viscosity. • Intersections of thermal volume expansivity dependences. • Density and viscosity properties of industrial fluids. In this paper, we have performed thorough analyses of volumetric and viscosity data for six oils. The volumetric data has been inspected by using two different equations of state, drawing a special attention to the intersection of the isothermal pressure dependences of the thermal volume expansivity, which were earlier reported for various materials in the liquid state. Each fluid is unique with respect to the other oils' relative composition, with those being either a pure liquid (Sebacate), or mineral oil with a proprietary blend of branched paraffins, napthalenes and aromatic molecules (Normafluid) or are undisclosed composition of mineral oil (MIN-H01 and MIN-H02) or are composed of fatty acid methyl esters (soybean biodiesel and rapeseed biodiesel). We have confirmed that the intersection points evaluated for different isotherms constitute a nonlinear curve for a given tested oil, and not any single point or straight line. Consequently, we have determined the temperature–pressure areas important from the application viewpoint, within which the thermal volume expansivity behaves differently, either increasing or decreasing with increasing temperature at a constant pressure. In the viscosity analysis, the parametrizations of the temperature–pressure dependences of specific volume based on the equations of state enabled to employ the density scaling idea in its simplest form of a power law of density γ /temperature, where γ related to an effective intermolecular potential is independent of thermodynamic conditions to a good approximation, which was successfully validated by various materials mainly in the supercooled liquid state, but also in the normal liquid and liquid crystal states in some cases. We have found that the scaling law giving prediction benefits relied on a linkage between macroscopic measurement quantities and effective molecular interactions is obeyed by the viscosity data of examined oils. Then, based on the prediction capabilities of the density scaling criterion, we have successfully explored the inflection points observed in some isothermal pressure dependences of viscosity measured for the oils in the temperature–pressure ranges that differ from those earlier reported for other materials. This intriguing finding observed in case of the experimental data for only some examined oils yields not only cognitive benefits, but it is also expected to exert an effect for instance on mechanical properties of the materials. Thus, our comparative discussion about the intersection and inflection curves provide a useful contribution to the further investigations of these thermodynamic and dynamic issues and other physicochemical properties of oils, which require gaining a better insight. [ABSTRACT FROM AUTHOR]

[Display omitted] • Ashless and non-corrosive organic disulfides derivatives. • Excellent anti-wear and extreme pressure performances. • Organic disulfides suitable to replace MCCP and ZDDP as EP additives. • FeS and FeSO 4 give effective protective film from organic disulfides. • The adsorption of π bond on the metal surface induce more sulfur molecules. Medium chain chlorinated paraffin (MCCP) and zinc dialkyl dithiophosphate (ZDDP) are widely used as extreme pressure (EP) additives in metalworking fluids (MWFs). Currently, sulfur-based EP additives are found to be more environmentally friendly and biodegradable. Although naphthenic base oil (NBO) is suitable to be used in MWFs due to its low pour point and better emulsified ability, there is a lack of study on the sulfur additives in this type of oil. In this study, two organo disulfides compounds namely dibenzyl disulfide (DBDS) and dioctyl disulfide (DODS) have been synthesized as EP additives. These DBDS and DODS demonstrate an excellent EP performance, non-corrosive, ashless, and good anti-wear (AW) properties in NBO. The DBDS shows 1961 N (EP value) and 6 mm2 (AW scar area) in NBO, which is superior to DODS, MCCP and ZDDP. This is due to the formation of sulfur-based tribofilm on the interface that acts as a protective sulfur layer thus, enhancing the property of EP. [ABSTRACT FROM AUTHOR]

[Display omitted] • Ferrite-based nanolubricants were studied tribologically using two tribo-pair contacts: steel-steel and silicon nitride-steel. • Ferrite-based nanoadditives enhanced the wetting behaviour of TOTM base oil. • The silicon nitride-steel and the steel-steel contacts showed the best anti-friction and anti-wear behaviour, respectively. • Tribofilm formation and repairing mechanisms produced by the nanoadditives were found to promote tribological improvement. In the present work, lubrication properties (friction and wear) of a synthetic ester oil, tris(2-ethylhexyl) trimellitate (TOTM) containing ferrite nanoparticles coated with oleic acid (F 3 O 4 -OA) were investigated for two different material pairs: steel ball-steel disc and silicon nitride ball-steel disc. Thus, four TOTM nanolubricants were formulated: TOTM + 0.010 wt% Fe 3 O 4 -OA, TOTM + 0.015 wt% Fe 3 O 4 -OA, TOTM + 0.020 wt% Fe 3 O 4 -OA and TOTM + 0.025 wt% Fe 3 O 4 -OA showing all of them a moderate time stability due to the oleic acid coating. Wettability behaviour of the ferrite-based nanolubricants on steel surface was analysed, revealing that the addition of Fe 3 O 4 -OA nanoparticles in TOTM decreases the contact angle between the steel surface and TOTM lubricant surface. Friction sliding tests were performed with the neat TOTM and with the formulated nanolubricants under a 20 N of load. All nanolubricants showed lower coefficients of friction than those reached with TOTM base oil for both material pairs. Worn area was significantly reduced for all Fe 3 O 4 -OA concentrations in the steel-steel contact and for the highest concentrations in the silicon nitride-steel contact. Specifically, the largest achieved reductions were for the TOTM + 0.010 wt% F 3 O 4 -OA nanolubricant: 43% reduction in friction (silicon nitride-steel) and reductions of 17% in wear track width, 42% in wear track deep and 36% in area (steel-steel). In addition, roughness analysis and Raman microscopy of the tested discs showed that tribofilm formation and surface repairing mechanisms occur. [ABSTRACT FROM AUTHOR]

• The investigation of viscosity and rheological properties of emulsions and nanoemulsions has been carried out. • The effect of the volumetric content and type of base oil on properties of the emulsion has been studied. • The influence of the type and concentration of the emulsifier on the properties of emulsions is considered. • The effect of ultrasonic treatment on the properties of emulsions has been studied. This study presents a systematic investigation of viscosity and rheological properties of several dozen emulsions and nanoemulsions. The concentration by volume of the oil in emulsions varied from 20% to 80%. Low-viscosity mineral oils were used for emulsion formation and an aqueous solution of calcium chloride was used as the second medium. The volumetric concentration of emulsifiers varied from 1.5% to 4.5%. Three types of mineral oil, as well as various emulsifiers, are considered. The effect of the volumetric content and base oil type, the emulsifier type and concentration and the ultrasonic treatment duration on colloidal stability, rheological properties and droplet size of the resulting emulsion has been studied. It is shown that emulsions are considered to be non-Newtonian fluids with apparent elastic properties at oil concentration less than 35 vol%. All other things being equal, the average droplet size in the emulsion increases with an increase in the base oil viscosity. The use of ultrasonic treatment makes it possible to reduce the average droplet size in the emulsion by 4.5 times and to reduce its viscosity by 1.5 times. [ABSTRACT FROM AUTHOR]

[Display omitted] • Eight nanolubricants based on two different pristine graphene nanoplatelets were tribologically studied. • Graphene nanoplatelets with larger lateral size showed better stability in the base oil. • 0.055 wt% nanolubricant concentration revealed the highest friction and wear reduction for GnP40 and for GnP7, respectively. • Tribofilm formation and surface repairing lubrication mechanisms due to nanoadditives were detected on the worn steel disks. This research is based on the investigation of the tribological properties of a biodegradable polymeric ester lubricant (BIOE) additivated with two different pristine graphene nanoplatelets (GnPs), named as GnP7 and GnP40. These GnPs have lateral sizes of 7 and 40 μm, and thickness of 3 and 10 nm, respectively. Four different nanoadditive loadings: 0.015, 0.035, 0.055 and 0.075 wt% have been used. Stability of nanolubricants has been investigated using the visual control and the refractive index evolution during time, revealing a slightly better stability for the nanolubricants formulated with the largest lateral size graphene nanoplatelets (GnP40). The influence of the thickness and lateral size of these carbon-based nanoadditives on the antifriction and antiwear capabilities of BIOE is analysed. For this purpose, rotational friction tests were taken with the eight nanolubricants under a 20 N working load and 340 m sliding distance. All nanolubricants showed friction coefficients and worn area lower than those previously reported for the unadditivated BIOE. As regards friction, the ideal loading for both GnPs was 0.055 wt% GnP, being the best anti-friction behaviour obtained using GnP40 as additive (up to 26% reduction), whereas the 0.055 wt% GnP7/BIOE nanolubricant leads to the best anti-wear capability with wear reductions up to 56%. Finally, from Raman microscopy and roughness assessments on the worn surfaces, it can be determined that the good tribological performance of nanolubricants is owing to the protective film formation and surface repairing mechanism. [ABSTRACT FROM AUTHOR]

. [Display omitted] • The study investigated oxidation stability of herbals oils in Bio-lubricants/fuels. • The experimental studies has shown Holy basil oil (HBO) as better anti-oxidant. • Use of DFT analysis to probe HAT and SET mechanisms in anti-oxidants. • Spectroscopy studies to identify the fuctional groups after oxidation test. • Rosmarinic acid in HBO exhibited both HAT and SET mechanisms simultaneously. Vegetable oils have been showing promising results as raw materials for the formulation of bio-fuels and lubricants, but they possess poor oxidative stability. This study aims to investigate the effect of various herbal oils on the oxidative stability of vegetable oils. The present study used Karanja oil as a base oil with herbal oils such as Ginger, Turmeric, Holy Basil, Clove, Tinospora Cordifolia and Black Pepper oil. The experimental study optimised the concentration of herbal oils in Karanja oil. The viscosity increments and FTIR results of all the optimum combinations after 120 h of the hot oil oxidation test were evaluated. A detailed quantum chemical calculation was done using density functional theory to understand the oxidation mechanism. The quantum chemical descriptors of major anti-oxidative components were evaluated. Out of all the additives, 2% of holy basil oil in Karanja oil has shown better oxidative stability. The quantum chemical studies justified the experimental data. [ABSTRACT FROM AUTHOR]

[Display omitted] • Deep eutectic solvents (DESs) of aminoguanidinium salt and fatty acid are addressed. • Higher mole ratio of fatty acid in DESs decreased viscosity and thermal stability. • DESs as additive to lube oil improved the lubrication by reducing friction and wear. • Surface analysis of worn scars revealed the formation of DESs-based thin film. Halogen-free, environmentally-friendly, and economically viable lubricant additives, which can furnish excellent miscibility with mineral lube base oils and enhance the tribological properties, are gaining increasing interest for the formulation of new generation lubricants. Herein, aminoguanidine salt-based deep eutectic solvents (DESs) having variable mole ratios of fatty acid (as a hydrogen bond donor; HBD) are synthesized through a single-step facile approach. The detailed chemical characterizations based on FTIR and NMR (1H and 13C) confirmed the synthesis of DESs via a hydrogen-bonding network. A linear correlation between the shear stress and shear rate implied Newtonian fluidic behaviour of these DESs. An increasing mole ratio of octanoic acid decreased the viscosity and thermal stability of resultant DESs. The long alkyl chain of HBD furnished good compatibility of these DESs with SN 150 mineral lube base oil. The DESs as additives to SN 150 mineral lube oil improved the viscosity index by 12% and enhanced the tribological properties for steel tribopair by decreasing the wear volume (94%) and coefficient of friction (30%). The detailed analyses of worn scars revealed the formation of DESs-derived tribochemical thin film. The low shear strength of DESs-derived lubricious and protective thin film between steel tribopair facilitated the sliding and avoided the direct contact between the steel tribopair, consequently, significant enhancement of tribological properties. [ABSTRACT FROM AUTHOR]

• Bio-degradable vegetable-based oils are 3rd generation insulating fluids in order to replace conventional mineral oil. • Dispersion of TiO 2 and ZnO results in enhancement of dielectric properties of vegetable oil based oil-blends. • Detailed statistical analysis of Weibull data regarding the failure probabilities confirms the experimental results. • TiO 2 and ZnO dispersed vegetable oils can be used as insulating fluids to improve the rating of transformers. Mineral oil being the most extensively used oil in transformers still has some associated drawbacks like non-biodegradability and low fire point. Bio-degradable, non-toxic and fire-resistant vegetable-based ester oils are considered as second-generation insulating fluids. These oils are continuously being tested in order to replace the conventional mineral oil for insulation purposes. The dielectric properties of these vegetable oils are further improved by adding various types of nanomaterials. This paper focuses on preparing a mixture of natural ester oil and mineral oil blend as a base fluid and studying the dielectric behavior of this fluid after being dispersed with TiO 2 and ZnO nanoparticles. Results indicated that dispersion of both nanomaterials resulted in an overall enhancement in the dielectric properties of nanofluids. The breakdown voltage of TiO 2 dispersed nanofluid is reported to be about 30% greater than pure mineral oil, 24% greater than pure ester oil, and 17% greater than the oil-blend. Likewise, the breakdown voltage of ZnO dispersed nanofluid is observed to be around 28% greater than pure mineral oil, 19% greater than pure ester oil, and 16% greater than the oil-blend. Moreover, in terms of cooling, TiO 2 dispersed oil-blend shows better performance as a coolant. Thus, both types of nanofluids can be used as insulating oils in the transformer depending upon the requirements expected to be met by the transformers. [ABSTRACT FROM AUTHOR]

[Display omitted] • A series of poly(ionic liquid)s brushes grafted carbon dots (CDs-PILs-X) were synthesized from the same batch of CDs-NH 2. • The anion species (X-) of CDs-PILs-X greatly influenced their tribological performance as additives of polyethylene glycol. • The CDs-PILs-OL with oleate (OL) exhibited the best tribological performance among the CDs-PILs-X. • The anions of OL- could form the densest absorbing anion layers on the contact asperities of steel/steel friction pair. • The OL- induced the CDs-PILs-OL to form the most compact boundary lubrication films on the rubbing surfaces. The tribological performance of poly(ionic liquid)s brushes capped carbon dots (CDs-PILs-X) as the additives of polyethylene glycol (PEG200) were well tailored by transforming the anion species (X-), where the X- were hexafluorophosphate (PF 6 -), bis(trifluorosulfonyl) imide (NTf 2 -), bis(salicylato) borate (BScB-) and oleate (OL-), respectively. Despite all of the CDs-PILs-X as additives of PEG200 exhibited excellent friction reduction and wear resistance properties, their tribological performance followed the order of CDs-PILs-OL > CDs-PILs-BScB > CDs-PILs-NTf 2 > CDs-PILs-PF 6. Typically, at a concentration of 2 wt%, the CDs-PILs-OL, CDs-PILs-BScB, CDs-PILs-NTf 2 and CDs-PILs-PF 6 made the average friction coefficient and wear volume of PEG200 reduce by 58.6 and 85.4%, 45.5 and 76.3%, 33.3 and 75.7%, and 28.6 and 72.6%, respectively, confirming the distinct influences of anion species on the tribological performance of CDs-PILs-X. The CDs-PILs-OL exhibited the best friction reduction and wear resistance performance because the anions of OL- with the lowest steric hindrance could form the densest absorbing layers and hence the most compact boundary lubrication films on the rubbing surfaces. The anions of PF 6 - and NTf 2 - might decompose to release corrosive substances (such as HF) during the friction process, largely weakening the lubrication functions of CDs-PILs-NTf 2 and CDs-PILs-PF 6. The CDs-PILs-OL can be a kind of promising lubricant additives for PEG200 because of their impressive performance, long service life, low cost and environmental friendliness. [ABSTRACT FROM AUTHOR]

• Dispersants interact differently with the ionic liquid additive P 66614 Dec. • Their behavior at a range of concentrations and temperatures were investigated. • Spectroscopic techniques showed P 66614 Dec to be fully encapsulated at 40 mol% PIBSA. • The IL/dispersants form reverse micelles and show a range of interactions. • The micelles are small, stable and monodisperse and reduce friction and wear. Fully formulated oils are used in the lubricant industry to enhance the effectiveness and efficiency in tribological contacts. Ionic liquids are currently being investigated as promising new additives and were formulated always with various additives to improve existing functionality of a base oil. However the interactions of ionic liquids with other additives have yet to be explored fully. In this work we have used 1H NMR, IR , DLS and UV–vis techniques to study the interaction of the phosphonium based ionic liquid trihexyl(tetradecyl)phosphonium decanoate (P 66614 Dec) with the dispersant additives polyisobutylene succinic anhydride (PIBSA) and polyisobutylene succinimide (PIBSI) at a range of concentrations and temperatures. The effect of these ILs/dispersant interactions on steel tribo-surfaces was also assessed. The dispersant additive PIBSA and PIBSI was not only able to improve the miscibility of the P 66614 Dec, further investigation showed that the ILs ion interaction was higher in the presence of PIBSA than PIBSI. This is proposed to be due to the differences in the dispersant head groups, with that of PIBSA resulting in more non-covalent interactions with P 66614 Dec, resulting in the formation of a self-assembled dispersant shell over the IL, where the size of the nanoaggregates is smaller than the larger neat ILs aggregates. The tribology testing showed that the ILs/dispersant additives were able to reduce friction and wear as compared to the base oil but there was marginal difference in friction and wear response between PIBSA and PIBSI. The results of this study shows that the use of different dispersants is a viable method for understanding the additive interactions and how this improves the understanding about the ionic liquid associations and improved shelf-life in base oil. [ABSTRACT FROM AUTHOR]

[Display omitted] • rGO and rGO@ODA were synthesized and characterized. • Hybrid nanolubricants present the best temporal stability due to the IL addition. • 34% maximum reductions in friction and wear are reached with hybrid nanolubricants. • Antifriction and anti-wear synergies are found between hybrid additives of BIOE. In the present work, antifriction and antiwear synergies of two functionalized graphene oxides (reduced graphene oxide, rGO, and reduced graphene oxide modified with octadecylamine, rGO@ODA) with a phosphonium ionic liquid (IL) as additives of a biodegradable ester base oil, BIOE, were investigated. For this aim, four BIOE nanodispersions were formulated: two nanodispersions without IL and two others with IL (hybrid nanolubricants), being the nanodispersions: BIOE + 0.05 wt% rGO, BIOE + 0.05 wt% rGO@ODA, BIOE + 1 wt% IL + 0.05 wt% rGO and BIOE + 1 wt% IL + 0.05 wt% rGO@ODA, and all of them showing good temporal stability (at least 3 weeks), especially those containing the ionic liquid. Tribological tests, under pure sliding conditions, were made with the aforementioned nanolubricants and with neat BIOE under a 20 N working load. All hybrid and non-hybrid nanolubricants resulted in lower friction coefficients compared to BIOE oil, with the largest friction reduction of 34% achieved by the 1 wt% IL + 0.05 wt% rGO nanolubricant. Discs lubricated with the prepared nanolubricants showed less wear than discs lubricated with BIOE, achieving the highest reduction (34%) in wear track width also for the 1 wt% IL + 0.05 wt% rGO nanolubricant. In addition, through confocal Raman microscopy, as well as roughness analysis of tested discs, it can be concluded that surface repairing, synergistic effect and tribofilm formation mechanisms occur. [ABSTRACT FROM AUTHOR]

• Nonequilibrium Molecular Dynamics simulation of a shear flow emphasizing the effect of the molecule branches. • Investigation of polyalphaolefin base oil wall sliding confined between iron surfaces. • Effect of temperature on the polyalphaolefin-iron lubrication system. In this paper, the slip length of branched hydrocarbon molecules, i.e., polyalphaolefin oils, under shear in a gap between iron surfaces were investigated utilizing large-scale Molecular Dynamics (MD) simulation. The results showed the expected singularity for the slip length with variation gap height. For large gap height, h → ∞ , the slip length approaches a constant asymptote λ → λ ∞. This study indicated that as the number of branches of the liquid molecule raise, the slip length λ → λ ∞ as well as viscosity increases. For given apparent shear rate, the friction force increased with increasing temperature due to the reduction of wall slip. MD Simulations demonstrate that the slip length of the polyalphaolefin-iron system increase by decreasing the liquid temperature, indicating an Arrhenius process. [ABSTRACT FROM AUTHOR]

[Display omitted] • Three phosphonium ILs separately combined with graphene nanoplatelets as hybrid additives in PAO 32 were investigated. • Hybrid additives improve the tribological performance of PAO 32 and of single additives. • 0.05 wt% GnPs and 1 wt% IL addition to PAO32 led to friction and wear reductions up to 36% and 27%, respectively. • Hybrid lubricants containing [P 6,6,6,14 ]+ led to the best combined capabilities. • Raman microscopy revealed protective tribofilms on the wear tracks composed by ILs and/or GnPs. Tribological performance of three ionic liquids (ILs), trihexyltetradecylphosphonium bis(2-ethylhexyl)phosphate (IL1), tributylethylphosphonium diethylphosphate (IL2) and trihexyltetradecylphosphonium bis(2,4,4-trimethylpentyl)phosphinate (IL3) combined with graphene nanoplatelets (GnP) as hybrid additives for a polyalphaolefin (PAO 32) base oil was studied. For this purpose, several dispersions were prepared by mixing, stirring, and then sonicating according to the following combinations: PAO 32 + (a wt%) IL + (b wt%) GnP, where a and b represent the concentration of the additives added to the PAO 32 base oil. In this study a is 0 or 1 and b is 0.05 or 0.1. Three PAO 32 + 1 wt% IL mixtures were also prepared. Thermophysical properties and stability against sedimentation of the dispersions were studied by means of a rotational viscometer and visual observation, respectively. Furthermore, friction and wear behaviors were analyzed using a ball-on-disk configuration tribometer operating in rotational mode and both a 3D optical profiler and a scanning electronic microscope, respectively. Confocal Raman microscopy was used to identify compounds in the tribofilms formed on the wear tracks. The hybrid combinations of PAO 32/ILs/GnP improved the friction reduction of the corresponding binary PAO 32/GnP nanolubricants and PAO 32/IL mixtures. Interestingly, the hybrid dispersions with low concentrations of GnP (with 0.05 wt% GnP) are more effective than those of 0.1 wt% GnP. Results also show that the addition of both 0.05 wt% graphene nanoplatelets and 1 wt% IL led to friction reductions up to 36% and wear reductions up to 27%, compared with the capabilities of neat PAO 32. IL1 and IL3, containing the trihexyltetradecylphosphonium cation, generate the hybrid lubricants with the best combined properties (stability, viscosity and tribological properties) of all the lubricants tested. [ABSTRACT FROM AUTHOR]

[Display omitted] • TMPTO viscosity at 150 MPa is around seven times higher than that at 0.1 MPa. • The pressure-viscosity coefficient for TMPTO is close to those of pentaerythritol esters. • Central film thickness increases when the entrainment speed grows. • TMPTO Stribeck curves were obtained for elastohydrodynamic and mixed lubrication. • The lowest friction coefficient is obtained adding 0.25 wt% of graphene nanoplatelets. Lubricant properties of trimethylolpropane trioleate synthetic base oil (TMPTO) were experimentally determined under different temperatures, pressures and rolling-sliding conditions. With the aim to obtain the viscosity-pressure coefficient, density and viscosity measurements were performed up to 150 MPa with a falling-body viscometer and a vibrating tube densimeter, respectively. Film thickness and friction properties were determined with a ball-on-disc apparatus from temperatures of 303.15 to 353.15 K, from slide-roll ratios from 5 to 50% at 50 N (applied load). Finally, it has also been evaluated if the use of nanoparticles as additives could involve changes on film thickness and Stribeck curves of TMPTO base oil. For this aim, hexagonal-boron nitride nanoparticles (h -BN) and graphene nanoplatelets (GnPs) were used at mass concentrations of 0.25, 0.5 and 1.0 wt%. The viscosity of TMPTO increases from 15 mPa s (at 10 MPa and 353.15 K) to 525 mPa s (at 150 MPa and 303.15 K). The Stribeck curves for TMPTO are placed between elastohydrodynamic and mixed lubrication. All nanolubricants show very similar Stribeck curves, being the lowest friction coefficient obtained for 0.25 wt% of GnP. It has been found that for most of the experimental conditions the addition of the GnP promotes an increase of the film thickness. [ABSTRACT FROM AUTHOR]

[Display omitted] • Tribological properties of ILs as additives and DES are reviewed. • Ionic liquids may outperform the commercial additives in lubricant oils. • Deep eutectic solvents have been successfully tested as lubricants. • Adsorption of ILs on the sliding surfaces was determinant for their performance. The growing concern with environmental issues and the rapid development of new engines accentuated the need for more efficient and green lubricants. Ionic liquids (ILs) have emerged as promising alternatives to the conventional lubricants due to their interesting properties. However, the manufacturing costs of ILs are usually high, making their application as neat lubricants impracticable. A viable solution to overcome this drawback is the application of ILs as additives to commonly used base oils. Another very attractive alternative is related to the deep eutectic solvents (DES), which have similar properties to ILs but are much cheaper and simple to prepare. This paper aims at reviewing the most relevant research done in the field of lubrication using IL additives and DES in the last 10 years (from 2011 to 2020). [ABSTRACT FROM AUTHOR]

• Essential oil based synthesis of metal nanoparticles. • Importance of essential oils. • Mechanism of formation of metal nanoparticles. • Pharmaceutical applications of metal nanoparticles. Biogenic synthesis of metal/metallic nanoparticles (MNPs) by reducing metal ions using secondary metabolites of plant essential oils is a single step and an eco-friendly approach. This biogenic synthesis of metal nanoparticles is somewhat fast, conducted readily at low temperatures and pressures, and a quite easy process. Metal nanoparticle synthesis using essential oils is environmentally-friendly or bio-safe. Essential oils (EOs) are complex lipids and contain a range of volatile and organic bioactive compounds, having huge applications in the medical, cosmetics and food industries. In this review, we have discussed the current developments on preparation of metal nanoparticles using essential oils and their biological properties in various applications. The various methods of nanoparticle characterizations are analyzed and potential applications of these nanoparticles are reviewed. [ABSTRACT FROM AUTHOR]

In this work, antifriction and antiwear capabilities of hexagonal boron nitride nanoparticles (h-BN) or graphene nanoplatelets (GnP) as additives of a polyalphaolefin neat oil (PAO 40) were studied at pure sliding conditions. For this purpose, eight PAO 40 nanodispersions were prepared: four nanodispersions with h-BN and four others based on GnP. The mass concentrations of these dispersions are 0.25, 0.50, 0.75 and 1.00 wt% of h-BN and 0.05, 0.10. 0.25 and 0.50 wt% of GnP, having all of them a good stability against sedimentation (at least 96 h). Tribological assays were carried with prepared nanolubricants as well as with PAO 40 base oil at 20 N load. All nanolubricants based on h-BN or GnP showed lower friction coefficients in comparison to the non-additivated neat oil, with a maximum decrease in friction of 21% for the 0.50 wt% GnP nanodispersion. Regarding the produced wear, all disks lubricated with nanolubricants showed lower wear than those lubricated using PAO 40. The greatest wear reduction in wear track width (22%) was also achieved for the 0.50 wt% in GnP nanolubricant. Moreover, through the confocal Raman microscopy and roughness analyses of worn disks it can be concluded that the wear reductions are due to the surface repairing and tribofilm formation mechanisms. [Display omitted] • The best friction and wear behavior was for the 0.50 wt% GnP nanolubricant. • Maximum friction and wear reductions of 21% and 22% were found for this lubricant. • For h-BN dispersions the best friction and wear reductions are 20% and 13%. • Surface repairing and tribofilm mechanisms occur due to nanoadditives. [ABSTRACT FROM AUTHOR]

In order to ensure the emulsification function of chemical flooding and simultaneously relieve the difficulty in demulsification of produced fluid in heavy oilfield, a pH-responsive surfactant HB-HA− (4-hydroxybenzaldehyde (HB) and n-hexylamine (HA)) was constructed based on dynamic imine bond. The molecular structure and its pH-responsive property was characterized by 1H NMR. Then, an emulsifier system CTAB/HB-HA− for heavy oil was fabricated by mixing hexadecyltrimethylammonium bromide (CTAB) with the constructed HB-HA− as the molar ratio of 1:1. The emulsification and pH-responsive property of the emulsifier were evaluated by macroscopic and microscopic appearance of heavy oil emulsion prepared under different pH, the surface tension (SFT) and interfacial tension (IFT) were determined to explore the pH response mechanism. The results showed that the emulsifier had strong emulsification and IFT reduction ability under pH = 12, and the emulsion can be stable for more than 48 h. As pH decreased to 5, the emulsion demulsified within 30 min. This emulsifier guaranteed good emulsification during recovery process and rapid demulsification property after the treatment process of produced liquid in the petroleum industry. • A pH-responsive emulsifier for heavy oil recovery based on imine bond is proposed. • The mechanism relies on the pH-regulated imine bond and electrostatic force. • The emulsifier contributes to the oil recovery and easy treatment for produced fluid. [ABSTRACT FROM AUTHOR]

A theoretical study considering Density Functional Theory and classical Molecular Dynamics simulations is reported on the study of the behavior of model poly-α-olefins base oils interacting with 2D MoS 2 monolayers. 2D materials offer a promising route to enhance anti wear and friction reduction. Among them, MoS 2 show a set of specially favorable properties. The objective of the present work is to develop a nanoscopic characterization to show the roots of the use of 2D MoS 2 monolayers as additives that reduce friction and wear with respect to plain lubricants. Three different types of hydrocarbons are considered, including the most relevant features of these oils: linear, star-like and branched compounds. The reported results show a large affinity of the three compounds for the monolayer surface, leading to very efficient adsorption guided by van der Waals interactions as well as by certain charge transfer toward the hydrocarbon. The development of adsorbed layers on the surface leads to changes in the base oil properties although being concentrated in a region close to the monolayer, with lower effects at larger distances. The presence of hydrocarbons with very different geometries hinders highly ordered molecular packing beyond the layer in direct contact with the surface. Nevertheless, the rearrangements on top of the MoS 2 surface will lead to large changes in the base oil behavior for lubrication purposes, enhancing tribological and anti-wear properties of MoS 2 nanosheet additivated poly-α-olefins base oils. [Display omitted] • Poly-α-olefins lubricant oils. • Nanoadditives with 2D MoS 2. • Adsorption of oils at the surface with layering and reordering. • Cooperativity effect upon adsorption. • Oils rearrangements in the vicinity of monolayers. [ABSTRACT FROM AUTHOR]

Ferrofluids consisting of stabilized iron oxide nanoparticles and insulating oils have emerged as a promising substitute for liquid dielectrics in electrical engineering applications. Recent enhancements of electrical insulating liquids rely on preparation of ferrofluids on emerging insulating oils available on the market. The present work reports on a comparative experimental study of insulating properties of a conventional mineral oil (MO)-based ferrofluid and a ferrofluid based on novel insulating oil produced by a gas-to-liquid (GTL) technology. The ferrofluids prepared on the two oils are subjected to rigorous experimental investigation of dielectric breakdown and partial discharges. The experiments are conducted on 4 MO-and 4 GTL-based ferrofluids with equal concentrations of magnetite nanoparticles. Measurements of partial discharges according to IEC 60270 are complemented with high frame–rate photography with positive streamer analysis. Based on the statistical analysis, it is found that MO-based ferrofluids exhibit superior breakdown performance to GTL-based ferrofluids, even though the pure GTL oil exhibits slightly higher mean breakdown voltage than the pure MO. A deeper analysis revealed a significantly greater number of partial discharges in GTL ferrofluids. The positive streamer size is lowered with increasing nanoparticle concentration only in MO-based nanofluids. Differences in the physical properties of the two oils, such as density, viscosity and permittivity, are considered in the interpretation of the different dielectric performance of the two ferrofluids. The experimental comparison leads to better understanding of the breakdown mechanism, and lay the foundations for proper selection of physical properties of a base oil for high performance insulating ferrofluids. • Dielectric performance of mineral oil and gas-to-liquid oil ferrofluids is compared. • Partial discharge quantities and visual corona in the ferrofluids are presented. • Dielectric breakdown is statistically analyzed. • Physical properties of the oils determine the dielectric performance of the ferrofluids. • Greater insulation enhancement due to magnetic nanoparticles is found for mineral oil. [ABSTRACT FROM AUTHOR]

This work investigates on the plausible interfacial mechanisms of PTFE (submicron particle) SMPs with the metal counterface during the growth of PTFE tribo-film. A series of submicron-oils was prepared to examine the effect on oil performance with variation in concentration of SMPs (0–9 wt%) in a Group III base-oil. Commercially available submicron suspension containing an adequate amount of dispersant for suspending the PTFE particles (avg size 230 nm) was used in various doses. In order to roughly estimate the shelf life of the formulated oils; UV–Vis spectroscopy technique was employed on the diluted oil samples since original samples were too thick. Dynamic light scattering (DLS) studies were carried in order to estimate the changes in the particle size with storage time. Nano-oils were characterized for their physical properties viz. (density, viscosity and viscosity index) and tribo- performance. Results revealed that 6 wt% of PTFE SMPs proved to be an optimum concentration for the highest EP performance with 392% enhancement compared to the base oil, which is not reported in the literature. To understand the mechanisms behind this performance, worn surfaces of pre-weld balls were inspected by FESEM (Field emission scanning electron microscope), 3D profilometry, goniometry and XPS (X-ray photo-electron spectroscopy), which revealed exact reasons for the varied performance of nano-oils as a function of increasing concentration of SMPs. XPS spectroscopy on worn surfaces revealed the formation of chemically modified tribo-film over the asperities. Furthermore, the thickness of tribo-film formed was also evaluated. Since EP trends were so promising, preliminary oils were characterized for AW and AF performance also. AW and AF performance got enhanced by 30% and 40% respectively. • Coalescence of PTFE particles around interfacial contact area in EP test. • Significant (400%) increment in EP-property for 6% PTFE particles as an optimum amount. • Chemical interaction of PTFE particles and metal counterface during EP action led to protective coating. • Shear-scission of PTFE molecules to form a tribo-chemical (FeF 2) film (>150 nm). • Higher the contact pressure, better was the anti-wear action (up to 164%) of particles. [ABSTRACT FROM AUTHOR]

The correct description of crude oil/water interfaces is a very complex and an important task, particularly to the oil industry, whose main difficulty relies on understanding how the interfacial properties (i.e., interfacial tension and interfacial accumulation) of the system are affected by a very large number of components. To give some additional insight to the oil/water interfacial behavior, eleven oil/water mixtures (i.e., six binary, four ternary and a quaternary mixture) have been modeled through atomistic molecular dynamics simulations at laboratory conditions. All mixtures were built with a model oil based on dodecane, toluene, quinoline and a naphthenic acid, to represent the saturated, aromatic, basic resin and acid resin fractions, respectively. The results from this contribution show that interfacial tensions can be correlated to interfacial accumulation, which can be used as good starting point in predicting interfacial properties of oil mixtures. Additionally, the interfacial properties of mixtures behave similarly to the most polar pure oil/water interface, while all other compounds stay in the oil bulk as spectators. This behavior raises the question of whether using common n-alkane oils is a good enough approximation for modeling the interfacial properties of crude oils. Unlabelled Image • Molecular simulation data for many oil/water unexplored mixtures is provided. • Interfacial accumulation of polar oil compounds depends on the matrix oil polarity. • The oil/water interfacial tension can be correlated with interfacial accumulation via MD simulations. • Interfacial properties of oil mixtures can be approximated by a simple Langmuir model. [ABSTRACT FROM AUTHOR]

In this work, six different types of protic ionic liquids (PILs) have been studied. For all these PILs, the bacteria toxicity and environmental biodegradability have been investigated, as well as their corrosive behavior and miscibility in different types of lubricating base oils. The PILs studied showed poor to moderate biodegradability (BOD 5 /COD from 0.072 ± 0.002 to 0.18 ± 0.01) and slight toxicity (TU values between from 1.18 ± 0.04 and 2.7 ± 0.1). However, these environmental properties are much better than those obtained for the reference lubricant additive used in industry (ZDDP). In addition, five of the PILs did not show corrosive activity on steel. Only one of the PILs showed some miscibility in an ester as a base oil and the rest of the mixtures were highly unstable. • The hexanoate-based PILs have higher biodegradability than the sulfonate-based ones. • These PILs show mild toxicity and are environmentally better than ZDDP. • These protic ionic liquids, with the exception of PIL-6, are not corrosive. • With the exception of PIL-3, the rest of PILs were immiscible in different base oils. • Protic ionic liquids could partially replace ZDDP as lubricant additive. [ABSTRACT FROM AUTHOR]

Functionalised graphene (AGO-C(n)), when paired with base oils, results in a product that is dispersively stable with enhanced tribological properties. Straight alkyl chains provided by octadecylamine (ODA), tetradecylamine (TDA), and decylamine (DA) were covalently attached to graphene oxide (GO) via the direct amidation process to synthesise amide-functionalised graphene oxide (AGO-C(n)). The attachment of the ODA, TDA, and DA at the surface of the GO was confirmed via the FTIR, XRD, TGA, Raman, and FESEM/EDX techniques. The hydrophobicity of AGO-C(n) was established via its higher contact angle relative to GO. Stable dispersion of AGO-C(n) in base oil after 30 days was confirmed by UV–vis technique. The AGO-C(n) demonstrated superior tribological behaviour relative to GO due to its high reduction of coefficient of friction (CoF) and wear scar diameter (WSD) of ~22% and ~61% (highest), respectively. Unlabelled Image • AGO-C(n) synthesised via a cost-effective and industrially scalable method. • The hydrophilic nature of GO converted into hydrophobic AGO-C(n) after amidation. • The dispersion and stability of AGO-C(n) in the base oil were greatly improved. • The AGO-C(n) demonstrated superior tribological behaviour. • The highest reduction of CoF and WSD was 22% and 61%, respectively. [ABSTRACT FROM AUTHOR]

Wettability alteration appears to be an important physiochemical process during low salinity waterflooding (LSWF) in carbonate reservoirs. However, the leading factor(s) behind wettability alteration remains unclear. In particular, the relative contribution of calcite dissolution induced pH and Ca2+ increase has not been explicitly quantified. We thus hypothesized that the pH increase plays a significant role in the wettability alteration, whereas the increase of Ca2+ plays a minor role. To test this hypothesis, we performed a geochemical study and examined the effects of salinity level on calcite dissolution and pH increase against the recovery factor profile obtained from the literature. The calcite dissolution was evaluated by equilibrating different brines with calcite. The equilibrated pH and brine compositions were then to be employed to quantify the Ca2+ increase and calculate surface species and electrostatic force between oil-brine-calcite interfaces. Our results show that low salinity water (LSW) indeed triggers calcite dissolution, which induces the pH increase from 1 to 2 units, whereas only causes less than 10% increase of Ca2+ concentration in the low salinity water. Surface complexation modelling implies that Ca2+ concentration variation may not lead to significant chemical surface species variation on calcite surfaces, but the pH increase would play an important role on oil-brine interfaces especially for the oils with high base component (-NH+). Moreover, geochemical modelling shows that at least 5 times dilution of the original brine is required to obtain a pH increase from 6.5–7.0 to 8.0–8.5, which seems to be essential for triggering the wettability alteration. We argue that high salinity formation brines with the low initial pH (5.5 to 6.5), high basic component oils, and at least five-time dilution could be the three key favourable elements to trigger the low salinity effect in carbonate reservoirs. This work provides a practical framework to screen potential carbonate reservoirs and predict LSWF performance. • Calcite dissolution mainly contributes to pH increase rather than salinity increase. • pH plays a primary role in oil-brine surface charge variations during low salinity waterflooding. • Salinity is the main driver of surface charge variations on calcite-brine interface in low salinity water. • At least 5 times dissolution of high salinity brine is preferred to observe wettability alteration in carbonate reservoirs. [ABSTRACT FROM AUTHOR]

The synthesis of insulating nanofluids by integration of nanoparticles in insulating oils has been employed over the last two decades by many researchers in an effort to improve both the dielectric strength and the thermal conductivity of dielectric liquids. In this paper, nanofluids with different volume concentrations of the nanoparticles were prepared by integration of semi-conductive TiO 2 nanoparticles into natural ester oil. Ultra-sonication and magnetic stirring were used for preparing homogeneous dispersions. AC, Lightning Impulse Breakdown Voltage and Partial Discharge Inception Voltage were measured and compared to the corresponding values of the base oil. Furthermore, the stability of the dispersions was studied ex situ by Transmission Electron Microscopy and in situ by Dynamic Light Scattering. Experimental results reveal the optimal TiO 2 nanoparticles' concentration in terms of breakdown voltage maximization, and future extensions of the current research are provided. • AC BDV of nanofluids is enhanced with highest maximization by 22.4%. • NF2 and NF3 present enhanced LI BDV with the highest maximization being 12.9%. • Paper impregnated to NF3 shows the greatest resistance to appearance of PD by 40%. • DLS shows agglomerates present an abrupt increase against time. [ABSTRACT FROM AUTHOR]

This work is about the use of two ionic liquids obtained from fatty acids (FAILs) as an additive at 0.5 and 2 wt% to a polyol ester (POE) base oil. Tribological tests under two different configurations (reciprocating and sliding/rolling "ball-on-disc") were performed at different temperatures and loads. Worn surface was measured and analyzed after reciprocating experiments by confocal and scanning electron microscopies and by X-ray photoelectron spectroscopy (XPS). Main results showed that these FAILs at low concentration did not change the viscosity of the POE and hence the tribological behaviors of the mixtures and the POE under elastohydrodynamic lubrication (EHL) in rolling/sliding tests were similar, but using mixtures resulted in lower friction regarding the POE under mixed lubrication regime; the friction behavior in reciprocating tests was similar with the use of all mixtures and the POE at 25 °C for the two loads used, while the mixtures outperformed the antiwear behavior of the POE; the antifriction behavior of the mixtures under both loads at 100 °C was slightly worse than that of the POE and all mixtures had better antiwear performance than the POE. • Two fatty acids anion-based ionic liquids (FAILs) were used as lubricant additive. • FAIL-based mixtures outperformed the antiwear behavior of the base oil. • FAIL additivation at low concentrations barely change the viscosity of the base oil. [ABSTRACT FROM AUTHOR]

In this study, viscosity of MgO/5 W30 nanofluid was investigated at a temperature range of 5–55°C with the solid volume fractions (SVF) of 0%, 0.1%, 0.25%, 0.5%, 0.75%, 1%, and 1.5%, and at a shear rate range of 666.5–13,330 s−1. Analysis of X-ray powder diffraction (XRD) pattern revealed that nanoparticles were in 41.28, 36.85, and 32.43 nm sizes. Results from the comparison of the viscosities of base oil and nano-lubricants indicated that the maximum viscosity increase (25%) occurs at a shear rate of 6665 s−1, a temperature of 15 °C and SVF of 1.5%. In addition, a decrease of 3.5% in viscosity was observed at the shear rate of 6665 s−1 and a temperature of 45 °C with SVF of 0.1%. The effects of the shear rate on viscosity indicated that this nanofluid exhibits non-Newtonian behavior of shear-thinning type at all temperatures and SVFs. Results from measurements shown that the viscosity of nanofluid decreases with increasing temperature, and the viscosity of nanofluid increases with increasing SVF. An empirical correlation was proposed for the prediction of nanofluid viscosity based on temperature, SVF, and shear rate. The R-squared value of the correlation was 0.9981 that means the proposed correlation can predict the nanofluid viscosity accurately. For a better understanding of the impacts of temperature and SVF on nanofluids, two separate sensitivity analyses were carried out for each parameter. Unlabelled Image • The viscosity of new multi-grid engine oil is investigated. • MgO nanoparticle is used as an additive in proposed engine oil. • Viscosity reduction of nano-engine oil is investigated in low concentrations of nanoparticles. [ABSTRACT FROM AUTHOR]