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This article reviews viscosity modifiers, additives that increase the viscosity of lubricating oils. Viscosity modifiers are high molecular weight polymers whose functionality is derived from their thickening efficiency, viscosity–temperature relationship, and shear stability. There are now many different additive chemistries and architectures avai...
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... Associative polymers are key components in a wide range of liquid formulations, as they impart non-Newtonian rheological behaviour to products such as paints 1,2 and lubricants 3,4 .Their useful properties arise from the formation of concentration-dependent self-assembled structures, 5 which have been studied by a range of techniques including dynamic [6][7][8] and static 6,7 light scattering, nuclear magnetic resonance, 9 fluorescence spectroscopy, 6,10,11 and rheology 5,6 . ...
The self-assembly of polymers is integral to their role in liquid formulations. In this study, we combine a dye whose lifetime is sensitive the nanoviscosity of its local environment with...
... In addition, the low drag reduction performance of PS samples may be caused by the high viscosity of the PS samples in crude oil (Fig. 5(a)) and intrinsic properties of this polymer. High viscosities of the solution can increase the viscous friction; therefore damping the amount of drag reduction at such regions (Martini et al., 2018, Dos Santos et al., 2020. Moreover, the intrinsic fragile structure of the polymers cannot dampen eddies' energy, so less drag reduction would be expected. ...
... Viscosity is a pivotal property of lubricating oil, acting as a crucial indicator of lubricating oil fluidity and internal friction. Viscosity values that are either too high or too low can detrimentally affect the lubricant's performance: increased viscosity may lead to heightened frictional forces during fluid lubrication, while reduced viscosity can decrease the lubricant's load-bearing capacity [9,10]. Breki et al. [11] integrated Einstein's viscosity equation with dynamic lubrication theory, elucidating the relationship between the friction coefficient and the solid-phase volume fraction, underscoring the significance of viscosity in fluid lubrication. ...
... In this case, the viscosity-reduction effect caused by interfacial slip is greater than the viscosityenhancement effect caused by the anti-shear effect of the nanoparticles, and the overall outcome would be a viscosity-reduction effect. (9) Equation (9), which incorporates the viscosity and aniline point of the base oil, facilitates the computation of the viscosity for base oils infused with a specific concentration of CuDDP nanoadditive at 40 °C, yielding an error margin of less than 1.7%. This level of precision marks a notable enhancement over traditional nanofluid viscosity estimation models. ...
In order to more accurately characterize the effects of nanoparticles on lubricant viscosity, the effects of copper dialkyl dithiophosphate (HDDP)-modified (CuDDP) nanoparticles on the dynamic viscosity of mineral oils 150N, alkylated naphthalene (AN5), diisooctyl sebacate (DIOS), and polyalphaolefins (PAO4, PAO6, PAO10, PAO40, and PAO100) were investigated at an experimental temperature of 40 °C and additive mass fraction ranging from 0.5% to 2.5%. CuDDP exhibits a viscosity-reducing effect on higher-viscosity base oils, such as PAO40 and PAO100, and a viscosity-increasing effect on lower-viscosity base oils, namely, 150N, AN5, DIOS, PAO4, PAO6, and PAO10. These effects can be attributed to the interfacial slip effect and the shear resistance of the nanoparticles. The experimental dynamic viscosity of the eight base oils containing CuDDP was compared with that calculated by the three classical formulae of nanofluid viscosity, The predicted viscosity values of the formulae deviated greatly from the experimental viscosity values, with the maximum deviation being 7.9%. On this basis, the interface slip effect was introduced into Einstein’s formula, the interface effect was quantified with the aniline point of the base oil, and a new equation was established to reflect the influence of CuDDP nanoparticles on lubricating oil viscosity. It can better reflect the influence of CuDDP on the viscosity of various base oils, and the deviation from the experimental data is less than 1.7%.
... During the operation of mechanical equipment, many factors can trigger the oxidative degradation of lubricating oils. These factors include internal oxygen and environment (temperature, pressure, and friction) as well as the metals in mechanical components [7,8]. The oxidation products of lubricating oils are various chemicals-for example, acids, esters, alcohols, and hydroxyl acids. ...
... The oxidation products of lubricating oils are various chemicals-for example, acids, esters, alcohols, and hydroxyl acids. Meanwhile, these oxidation products might further condense to form high molecular compounds, increasing lubricant viscosity and mechanical component friction [7,9,10]. Furthermore, these high molecular compounds have low solubility in lubricating oils, resulting in the formation of paint films, carbon deposits, and organic acids, thereby corroding and wearing metal parts [11]. ...
Lubricating oils play an important role in friction-reducing and anti-wear, as well as enhancing mechanical efficiency. To improve the oxidation stability and service life of lubricating oils, the composition and structure of antioxidants should be strategically designed, and these parameters have significantly affected the performance of antioxidants in lubricating oils. Antioxidants are classified into two types based on the substrates they act on: peroxide decomposers and radical scavengers. In this review, the effects of peroxide decomposers (including sulfur compounds, phosphorus compounds, sulfur–phosphorus compounds, and sulfur–nitrogen compounds) and radical scavengers, such as hindered phenols and aromatic amines, have been discussed as additives in the antioxidant properties of lubricating oils. The results indicate that peroxide decomposers have excellent performances in lubricating oils, but high pollution of S and P is not conducive to their widespread use. On the contrary, radical scavengers also have superior antioxidant properties and no pollution, possessing the potential to replace traditional antioxidants. In addition, molecular structures with (multiple) synergistic antioxidant properties have been extensively designed and reported. This review serves as a reference for researchers to design and develop high-end new antioxidants.
... The decline in lubricant viscosity with increasing temperature can be a significant issue for lubricants susceptible to varying temperatures over the course of its use [37,38]. The viscosity index (VI) serves as an indicator of polymer viscosity fluctuation between low and high temperatures [39]. ...
... The chemistry of viscosity modifiers (VMs) comprises polyalkyl methacrylate (PAMA), olefin copolymer (OCP), polyisobutylene (PIB), and hydrogenated styrenediene (HSD). The molecular weights of mentioned polymers are typically greater than 10,000 g mol − 1 [37]. ...
... FIs hinder wax crystal formation, and inhibit the development of complicated interconnecting networks. Viscosity is another critical property of lubricating fluids [14]. A fluid's viscosity changes depending on temperature, and it is necessary to maintain a wide variety of lubricant viscosities within the optimal performing conditions of the apparatus being used [15,16]. ...
... The reliance of the viscosity of lubricant upon temperature is quantified using the Viscosity Index (VI), an empirical variable describing the lubricant's application temperature range [18,19]. The Lubricants that have higher VI values exhibit an increase in viscosity resistance to changes regarding temperature variations and are generally prominent in the majority of mechanical systems [14,20]. ...
A novel pour point depressant was synthesized by developing a polymeric nanocomposite using polymethacrylate and magnetite nanoparticles. The primary objective was to assess and compare the efficacy of PMA and PMA/Fe3O4 nanocomposite in reducing the gelation point, yield stress, apparent viscosity, and pour point of waxy crude oil. Extensive assessments were conducted to evaluate the performance of these additives. Rheometry tests were employed to measure the pour point of the lubricating oil pour point following the addition of PMA and PMA/Fe3O4 nanocomposite. The findings demonstrated a significant reduction in pour point, reaching values of − 18 °C, − 27 °C, − 24 °C, and − 36 °C for CP1, CP2, NP1, and NP2, respectively, at an optimal concentration of 10,000 ppm. Various characterization techniques such as Fourier Transform Infrared Spectrometer, Proton Nuclear Magnetic Resonance, X-ray Diffraction, Scanning Electron Microscope, Differential Scanning Calorimetry, Dynamic Light Scattering, Polarized Optical Microscope, and Gel Permeation Chromatography were utilized to analyze the polymers. Furthermore, the effectiveness of each polymer as a viscosity index improver (VII) and pour point depressant for mineral-based oil was evaluated. The mechanism of action of the polymers as pour point depressants was investigated through photomicrographic analysis. Additionally, the rheological properties of the formulated lubricant were assessed and reported. Thermogravimetric analysis was used to determine the thermal stability of the polymers, revealing that the copolymer nanocomposites exhibited higher thermal stability, viscosity index (VI), and molecular weights compared to the copolymers alone. These enhancements in thermal stability and molecular properties contributed to the improved pour point depressant (PPD) properties. Overall, the study successfully synthesized a novel pour point depressant and evaluated its performance using various tests and characterization techniques. The results demonstrated the effectiveness of the additives in reducing the pour point and improving the thermal stability of the lubricating oil.
... The elevated viscosity of BHOSO in comparison to HOSO can be attributed to the presence of an alkyl branch, which could impede the flow of molecules and result in a higher kinematic viscosity [41]. Another possible explanation for the higher viscosity of BHOSO is the presence of oligomers in BHOSO [53]. The molecular weight of methyl oleate from HOSO and i-Pr branched methyl stearate from BHOSO are 296 and 340 respectively (refer to Figure 6). ...
Soybean oil is currently being studied as lubricating oil in various industries, including automotive, aerospace, and UAV applications, due to its renewability, biodegradability, and non-toxicity. In vegetable oils, the vast...
... Polymer additives have been used as viscosity index improvers for decades [6][7][8]. Viscosity index improvers are used to control the temperature dependence of lubricant viscosity and maintain an appropriate viscosity range within the expected operating temperature. This is necessary to maintain an oil lm under hydrodynamic lubrication conditions. ...
... The results showed that the viscosity index increased by a factor of three for a gap of ≤ 10 nm. The viscosity index improvement effect of PAMA in the bulk state has been interpreted as the swelling of molecules and an increase in ow resistance with increasing temperature, which resists the decrease in viscosity of the base oil [7]. As mentioned previously, Figs. ...
Adsorptive polymer additives have been reported to improve the retention capacity of oil films under hydrodynamic lubrication and to reduce friction under boundary lubrication. These effects are believed to result from the formation of a polymer adsorption film on the surface that acts as a lubricious coating. Polymer adsorption films have become dominant in nanometer-order microscopic gaps. However, their mechanical properties are difficult to quantify. This hinders the development of polymer additives. In our previous study, we successfully measured the shear viscoelasticity of lubricants (base oils) sheared in nanogaps using an originally developed measurement method called the fiber wobbling method (FWM). In this study, we measured the shear viscoelasticity of polymer-added lubricants in nanogaps by using FWM. In addition, we developed a heating stage in the FWM to quantify the temperature dependence of shear viscoelasticity in nanogaps. As a result, the viscosity index improved and elasticity was observed in the nanogap, where the polymer adsorption film was dominant. Furthermore, our results indicate that the elasticity of the adsorbed polymer film originates from entropic elasticity.
... Also, the GO nanosheet additives can be considered as an alternative VI improver because they have sufficient shear stability due to their inter-sheet shearing ability and high load-carrying capacity [71]. Thus, they do not degrade easily and lose their effectiveness during severe engine running conditions compared to polymer type VI improvers [78]. Fig. 7 shows the variations in the thermal conductivity coefficients of the base engine oil with different GO nanosheets additive concentrations at temperatures from 20 to 100 • C. As illustrated in Fig. 7-A, the thermal conductivity of all prepared samples increased almost linearly with an increase in temperature. ...
... The hydrodynamic lubrication regime develops in internal combustion engines mainly in the crankshaft journal bearings and in some conditions in the piston skirts [8,9,42,43]. Under various engine operating conditions, the oil films tend to shear thinning at high shear rates present in engine components with low engine oil viscosity and high VI [71,76,78]. These reduce friction losses and have a significant effect on mechanical engine efficiency and fuel saving. ...
This study investigates the effects of graphene oxide (GO) nanosheets as an engine oil additive in fully synthetic SAE 10W-40 engine oil. GO concentrations in 0.5, 1.0, 1.5, and 2.0 mg/mL were added. The viscosity index (VI) increased by up to 7 % and thermal conductivity by 4-15 %. Tribological tests with a ball-on-disc mechanism showed that 1.5 mg/mL GO nanosheets additive gave the best results in reducing the coefficient of friction (COF) by 17 % and the total wear mass loss by 44 % on average. Based on the engine friction tests on the dynamometer, GO nanosheets reduced motored torque by up to 6 %, which represents the engine frictional losses, and improved mechanical efficiency by up to 2.8 % at certain engine speeds. An average improvement of 2.6 % in brake-specific fuel consumption (bsfc) and 2.7 % in brake thermal efficiency (bte) was observed across all engine speeds. The results of detailed engine tests suggest that the GO nanosheets additive has the potential to enhance the mechanical efficiency of internal combustion engines, leading to energy and fuel savings and indirectly contributing to reducing CO 2 emissions.
... Lubricant oil performance is critical for machinery and engine longevity in a wide range of industrial and commercial applications [1]. The viscosity index (VI) is a key parameter that evaluates the effectiveness of lubricant oils, representing the degree of viscosity change as a function of temperature [2]. ...
This study investigated polyethylene glycol (PEG), as a polymer improver of the paraffinic oil viscosity index (VI). The characterization of PEG/paraffinic oil blends at different concentrations (0%, 1%, 2%, 3%, 5%, and 10%), was performed using Raman spectroscopy and optical microscopy. The rheological parameters as the viscosity index and activation energy were determined using the kinematic viscosity measurements. Results showed that the VI improvement reached an optimal value for the blend containing 3% PEG, with greater value for blends containing 2% PEG than 5 and 10% PEG. The presence of polymer particles was observed by optical microscopy, which confirmed the lack of PEG distribution in the blend containing 5%, and more, whereas mixtures with 3 and 2% PEG exhibited good particle distribution, evidenced by smaller polymer particle sizes. This finding was corroborated by Raman spectroscopy, which revealed the absence of polymer–oil intermolecular interactions in the PEG/paraffinic oil blends. The rheological tests showed that increasing the blend temperature from 40 to 80 ℃, improved the PEG chains dispersion in the paraffin oil, for the blends containing up to 3% PEG. The difference of the activation energy of the pure paraffinic oil and the PEG/paraffinic oil blends, (ΔEa) was calculated, and the correlation between the ΔEa and the viscosity index values was established. Therefore, adding PEG to paraffinic oil appeared to be promising for the viscosity index improvement and promote industrial applications of paraffinic oil.
