Boundary lubrication performance of fatty acid and its derivatives using energy dissipation method

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The influence of molecular structure variation in terms of functional groups, branching and molecular weight on the frictional behavior of these Organic Friction Modifiers (OFMs) at elevated temperatures (40˚C, 70˚C, and 100˚C) has been studied. A custom-built Force-Controlled Pendulum Tribometer (FCPeT) was used to evaluate the friction of the OFMs at a concentration of 0.1% w/w in group III (32 cSt) base oil. The results demonstrated repeatable frictional response which varied significantly with temperature. At 40˚C, the stability of adsorbed film was found to be eminent, leading to lower friction for molecules with higher packing efficiency. At 70˚C, the molecular weight was found to be critical, owing to its inverse relation with desorption rate, leading to stronger adsorbed films. For a higher temperature of 100˚C, the ability to chemisorb was found to be important to achieve lower friction. Erucic acid and its estolide and estolide ethanolamide derivatives were found to perform efficiently across the range of temperatures studied. The study concludes that the molecular structure significantly influences the efficiency of the OFMs, with the ability to chemisorb onto the metal surface, higher molecular weight and low branching being the desired features for optimal performance of OFMs. Estolides Estolide ethanolamides Organic friction modifiers Boundary lubrication Force-Controlled Pendulum Tribometer Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 1. Introduction Boundary lubrication (BL) illustrates a critical regime where the surface asperities primarily carry the load between two contacting surfaces. The characteristic features that lead to BL are low speeds and higher loads. These conditions can lead to excessive heat, wear, and potential seizure. To mitigate the high friction and wear, OFMs are added to the lubricants. These OFMs have an affinity towards the metal substrates, thus adsorb on the surface and form a protective film that lowers the direct metal-to-metal contact while dissipating the shear forces [ 1 ]. OFMs are amphiphilic molecules possessing a polar head group and a long hydrocarbon chain. The effectiveness of OFMs is influenced by molecular structure in terms of the functional groups, packing efficiency, and their molecular weights [ 2 – 10 ]. The most prominent functional groups reported are carboxylic acids, alcohols, esters, amines, amides, and ethanolamides [ 1 , 5 , 11 ]. Fatty acids are the most effective OFMs wherein their carboxyl head group forms strong chemisorptive bonds with metal oxides [ 7 , 12 ]. Similar chemisorbed bonds with metal oxides are formed by amide-based OFMs [ 13 ]. While the hydroxyl group of alcohols forms hydrogen bonds with metal oxide surfaces, the overall adsorption is weaker than acids and amides [ 3 , 14 ]. On the other hand, the ethanolamide-based OFMs have enhanced adsorption due to hydrogen bonding of the hydroxyl group along with chemical interaction of the amide moieties [ 3 ]. Also, esters are used owing to their ability to adsorb on metal surfaces and provide excellent film coverage [ 15 ]. Quite recently, a new class of polymeric friction modifiers has been evaluated as OFMs. These molecules consist of multiple polar groups across a high molecular weight chain, leading to multivalent adsorption capabilities [ 6 , 16 ]. Fatty acids having either unsaturation or hydroxy groups can be oligomerized into Estolides by the formation of secondary ester linkages while preserving a carboxyl moiety [ 17 – 24 ]. Conventionally, estolides derived from oleic acid and ricinoleic acid have been extensively studied for their potential utility in lubricants [ 25 – 33 ]. Recently, estolides derived from undecylenic acid and 12-hydroxystearic acid have been studied for their tribological properties [ 17 , 19 , 21 ]. But there is scarce literature regarding estolides derived from erucic acid [ 34 ]. Essentially, the formation of estolides is accompanied by a reduction in unsaturation or hydroxyl group (as relevant to the chemistry) and an increase in molecular weight as well as branching. Estolides have been reported to form protective layers due to their polarity and branched ester linkages. Moreover, the steric hindrances and higher molecular weight aid in lubricant integrity under mechanical stress [ 35 ]. Thus, this reduction in unsaturation, increased branching, and molecular weight has been reported to improve the lubricity, especially in the BL regime [ 2 , 19 , 36 ]. Owing to the free carboxyl moiety, estolides can be further derivatized to various molecules, including esters, soaps, and amides. Although extensive studies of estolide esters [ 17 , 21 , 44 , 25 , 37 – 43 ] and a few studies related to estolide soaps [ 45 ] have been reported, the amide derivatives of estolides have not been explored. The dual activity of the ethanolamides, combined with the polymeric structure of estolides, could potentially aid friction modification in BL and thus needs to be studied. The boundary lubrication (BL) regime requires precise study since asperities interact directly. Conventional tribometers face limitations in replicating real tribo-contacts, as motors and direct-contact sensors can alter true interface conditions. Moreover, the BL regime is highly sensitive to the mode of motion, force-controlled or displacement-controlled, during sliding. Lubricant performance in this regime is better captured under force-controlled motion [ 46 ]. To address these challenges, a custom-built FCPeT was employed in the present study [ 46 ]. In the current study, estolides of undecylenic, oleic, erucic, ricinoleic, and 12-hydroxystearic acid were synthesized and further derivatized to monoethanolamides. The fatty acids and their respective estolides and estolide monoethanolamides were then evaluated as friction modifiers in the BL regime at a 1000 ppm dosage level in group III base oil. The frictional evaluation was carried out at 40˚C, 70˚C, and 100˚C with the aid of FCPeT using the energy dissipation method. 2. Materials and Methods 2.1. Materials Oleic acid (75%) and erucic acid (90%) were obtained as samples from Godrej Industries Ltd. Ricinoleic acid and 12-hydroxystearic acid were obtained as samples from Gokul Agro Resources Ltd. Undecylenic acid was procured from Prime Chemicals, Karnataka. Sulfuric acid (CAS No. 7664-93-9), ethanolamine (CAS No. 141-43-5), and sodium methoxide (CAS No. 124-41-4) were procured from SD Fine Chemicals. SN 150 (group 2, ISO VG 32) base oil was procured from BSM Lubricants. Hexane, ethanol, and other solvents used were of commercial grades. For the frictional study, an EN 31 steel block (42.5 × 30 × 15 mm) was utilized as a disc after surface finishing as described in section 2.6.1. A high-carbon chromium steel pin with a radius of 6 mm and surface roughness of 90 nm was utilized as the counter-surface. 2.2. Synthesis of unsaturated fatty acid estolides Unsaturated fatty acid (undecylenic acid/ oleic acid/ erucic acid) and sulfuric acid (0.6 mole equivalent) were added to a flask. The mixture was agitated at 300–400 rpm using an overhead stirrer at 50˚C for 4 hours. The reaction was carried out under the influence of 25 kHz (225W) ultrasonication provided through a water bath. After the completion of the time period, the reaction mixture was transferred to a separation funnel, and hexane was added. The organic layer was given multiple hot brine washings to remove the acidic catalyst. The organic layer was dried over an anhydrous sodium sulfate bed, and the solvent was removed using a rotatory evaporator to get estolides. 2.3. Synthesis of hydroxy fatty acid estolides Hydroxy fatty acids (ricinoleic acid/ 12-hydroxystearic acid) were added to a flask, heated to a temperature of 180˚C, and agitated at 300–400 rpm using an overhead stirrer for 8 hours. A Dean and Stark apparatus was used to remove the water of reaction with the aid of a vacuum (500–600 mm Hg). After 8 hours, estolide with desired oligomerization was obtained and used for further analysis. 2.4. Synthesis of estolide ethanolamides Estolide and ethanolamine (1:1.1 mol) were added to a flask and heated to 180˚C under constant agitation of 300–400 rpm using an overhead stirrer. Sodium methoxide (0.1%) was used as a catalyst for the reaction. A Dean and Stark apparatus was used to remove the water of reaction. The reaction was carried out for 8 hours, and at the end of the reaction vacuum (500–600 mm Hg) was utilized to remove the excess of ethanolamine added to the reaction. After cooling, estolide ethanolamides were obtained. 2.5. Instrumental characterization The structure of estolides and ethanolamides was confirmed with the aid of FTIR spectra obtained using a PerkinElmer 100-FTIR Spectrometer over a wavelength range of 650 to 4000 cm -1 and NMR spectra using an Agilent ProPulse at 500 MHz using CDCl 3 as a solvent. 2.6. Forced Controlled Pendulum Tribometer (FCPeT) As shown in Fig. 2 , FCPeT was employed to evaluate the energy efficiency of synthesized friction modifiers in the boundary lubrication (BL) regime. The FCPeT consists of a pendulum mounted on a horizontal shaft supported by ball bearings. One end of the shaft holds the test sample, while the opposite end is connected to a high-resolution rotary encoder (0.000219°), which precisely records the pendulum’s angular position. A pulley–mass-based load assembly applies a controlled normal force at the tribo-contact, ensuring accurate loading conditions. The pendulum is displaced by a known angle to introduce potential energy, which is subsequently dissipated by the system during oscillation. To differentiate the energy loss due to tribo-contact friction from other system losses, a two-step baseline correction procedure was employed: System damping experiment: The tribo-contact was kept apart (no sliding) while the sample was immersed in lubricant, and the decay response of the pendulum was recorded. This measured the dissipation of energy solely due to system damping. Sliding experiment: The tribo-contact was engaged, and the pendulum damping was recorded again. This included the combined effects of system damping and tribo-contact friction. By subtracting the first case (system damping) from the second (system damping + tribo-contact), the net energy dissipation due to tribo-contact friction was isolated. This correction accounted for bearing friction, system damping, air drag on the pendulum shaft, and viscous drag from the base oil. The frictional loss per cycle was calculated from the reduction in potential energy (amplitude decay) of the pendulum swing. Normalizing this loss with the sliding distance per cycle yielded the frictional loss per unit distance. The coefficient of friction (COF) was then obtained by dividing this value by the applied normal load and plotted as a function of average sliding velocity. A more detailed description of this methodology is provided by Divarakan et al. [ 46 ]. 2.6.1. Preparation of Lubricant and Disc Samples The fatty acids, estolides, and estolide amide derivatives were blended in VG 32 group III base oil at a dosage level of 0.1% w/w. The blending was carried out at an elevated temperature of around 60–70˚C under constant agitation till the OFMs were dissolved to homogeneity. For tribo-contact, a flat EN 31 steel plate was utilized, considering its wide use in machinery tribo-contacts. To achieve consistent surface topography, the flat samples were prepared by polishing using a progression of emery sheets from coarser 220 to a mirror finish grit size of 4000. The polishing process involved 50 unidirectional sliding passes for each emery sheet sequentially in order of 220, 320, 400, 800, 1000, 1200, 1500, 2000, 2500, 3000, and 4000. For the counter surface, a 6 mm diameter high-carbon chromium steel ball was utilized. Before initiating the experiment, the plate and ball were thoroughly cleaned with hexane to eliminate the impurities present on the surface. 2.6.2. Experiments using FCPeT Table 1 Experimental Configuration Testing parameters Value Running-in 10 repetitions (20˚ to 15˚) Normal load \(\:1\:N\) Release angle 15˚ Angular resolution 0.000219 \(\:^\circ\:\) DAQ (Angular position of the pendulum) \(\:100\:kHz\) Maximum sliding velocity \(\:13\:mm/s\) Lubricant Temperature 40, 70 & 100˚C The experiments were carried out as per the experimental setup, as shown in Fig. 1 , using the configuration provided in Table 1 . For system damping experiments, the pendulum was released from an angle of 15˚, and the damping of the pendulum was recorded using the optical encoder. Similar system damping experiments were carried out submerging the disc samples in the base oil at temperatures of 40, 70, and 100˚C, respectively. No normal load was applied during these experiments. For sliding experiments, the lubricant was first heated to the desired temperature. The normal load of 10 N, equivalent to 0.9 GPa maximum contact pressure, was applied to the disc using the pulley mechanism. Before initiating measurements, the contact surfaces were run in by oscillating the pendulum 10 times from an initial angle of 20˚ to 15˚ to ensure a steady state during measurement. Following the run-in period, each experimental trial was initiated by releasing the pendulum from an initial angle of 15˚. The subsequent angular position was recorded at a sampling rate of 100 kHz until the pendulum came to a complete rest. For each lubricant at a specific temperature, the experiment was repeated in triplicate to ensure repeatability. The recorded angular displacement with time was then utilized to determine the COF using the energy dissipation method as reported by Divakaran et al. [ 46 ]. For the calculation, a single cycle was considered. The energy loss over the cycle was determined using the change in potential energy (decrease in amplitude). The energy loss due to the other factors, as determined by system damping experiments, for an equivalent amplitude of cycle, was subtracted to get the energy loss at the tribo-contact. The distance covered by the pin over the plate during the cycle was calculated using the angular displacement data and the radius (15 mm from the axis). The calculated frictional loss for the cycle was divided by the applied normal load (10N) and the sliding distance to get the COF. The COF calculated for different cycles for each lubricant from 15˚ till the motion of the pendulum ceases was plotted against the average sliding velocity (calculated using the derivative of the damping curve). 3. Results and Discussion 3.1. Synthesis of estolides Table 2 1 H-NMR spectra for estolides Component Chemical Shift Integral UE OE EE RE HE -CH 3 0.87–0.89 6.00 6.00 6.00 6.00 6.00 -CH 2 - 1.18–2.02 43.14 46.59 64.63 45.66 57.75 –CH 2 –(C = O)–O–CH 2 – (α-methylene ester) 2.26–2.27 3.41 1.62 2.11 3.60 2.25 –CH 2 –(C = O)–OH (α-methylene acid) 2.34 2.59 2.22 2.11 3.60 1.88 –CH 2 –(HC-OH)–CH 2 – 3.59–3.62 - - - 0.44 0.75 –CH 2 –(C = O)–O–CH 2 – (ester methine) 4.83–4.87 1.46 0.71 0.95 1.02 1.13 -CH = CH- (alkene) 5.37–5.38 0.65 1.06 1.05 1.76 - synthesizedbased on undecylenic (UA), oleic (OA), and erucic acid (EA) were synthesized with the aid of ultrasonication under the catalytic activity of sulfuric acid as per the method mentioned in section 2.2 [ 20 , 47 ]. While estolides based on ricinoleic acid (RA) and 12-hydroxystearic acid (HA) were synthesised by homo-polymerization at elevated temperatures without the use of any catalyst [ 21 ]. The formation of estolides was confirmed with the aid of 1 H-NMR (Table 2 ) and FTIR (Fig. 2 ). For 1 H-NMR spectra of all the estolides, two distinct chemical shifts in the range of 2.20–2.40 ppm confirmed the formation of the ester linkage (2.26–2.27 ppm) along with unreacted carboxylic acid (2.34 ppm). Moreover, the peak associated with ester methine in the range of 4.86–4.87 ppm confirmed the formation of estolide. The disappearance of the peak related to terminal unsaturation of UA can be linked with the bond migration during estolide formation [ 19 ]. Also, the FTIR spectra {Figure 1 (a) & (b)} illustrate the shift in absorbance from 1700–1710 cm − 1 (C = O stretching for carboxyl, acid) to 1730–1740 cm − 1 (C = O stretching for carboxyl, ester) linked to the formation of estolide linkages. Also, absorbance at 1175–1180 cm − 1 (C-O stretching, ester) confirmed the formation of estolide. The sharp peak 909 cm − 1 (C = C bending) associated with unsaturation observed in the case of undecylenic acid disappeared in the case of undecylenic estolide (UE), confirming the reduction in unsaturation as a result of estolide formation. Similarly, the disappearance of the peak associated with unsaturation was observed by oleic (OE) and erucic estolides (EE) in comparison to their acid counterparts. Since the polymerisation reaction associated with the formation of estolides yields a mixture of monomer, dimer, and higher oligomers, the synthesised estolides were characterised by their average estolide number (EN), as determined using the Acid Value (AV) and ¹H-NMR [ 19 – 21 , 48 ]. The average estolide number is as mentioned in Table 2 . Except for UE and OE, the EN for estolides is around 2, which correlates to the formation of dimeric molecules. In the case of OE, the lower oleic content (around 75%) led to the formation of estolide with slightly lower EN. While in the case of UE, the lower molecular weight (MW) of undecylenic acid led to faster reaction, leading to an estolide with higher EN. The Average EN was then used to determine the average MW of the synthesised estolides (MW = 56100/AV Average EN ). Table 3 Estolide number and molecular weight of synthesised estolides Sample Acid Value (mg KOH/g) EN* using the Acid Value Method EN* using the ¹H-NMR method Average EN* Average Molecular Weight # (g/mol) UE 113.27 2.62 2.31 2.47 466 OE 107.59 1.74 1.73 1.74 520 EE 72.57 2.30 2.00 2.15 722 RE 88.69 2.12 2.00 2.06 616 HE 86.58 2.15 2.20 2.18 658 * EN – Estolide Number # Average molecular weight calculated based on the Average EN 3.2. Synthesis of estolide monoethanolamides Synthesis of ethanolamide derivatives of fatty acids has been extensively studied [ 49 – 53 ]. But ethanolamide derivatives of estolides have not been reported earlier. The ethanolamides were synthesized using the catalytic activity of sodium methoxide at elevated temperatures. The synthesized products were evaluated for the conversion and selectivity towards amide formation with the aid of AV and Amine Value as shown in Table 3 . The synthesized amides were found to have conversion in the range of 78–86%. Wherein the estolides derived from UA, OA, and EA had higher conversions in comparison to the hydroxy-based estolides. The underlying reason could be the presence of a free hydroxyl group within the estolide molecule of ricinoleic estolide (RE) and 12-hydroxystearic estolide (HE), in addition to the alcohol group of ethanolamine, competing with the amidation reaction. Thus, the ester content for the hydroxy-based estolide amides was observed to be higher in comparison to the other estolides. Overall, the reaction attained more than 90% conversion in 8 hours with an average amide to ester selectivity of 7.4:1. Table 4 Analysis of Estolide Amides Sample Amine Value (mg KOH/g) Acid Value (mg KOH/g) Conversion (%) Amide Ester Total UEA 16.30 9.89 83.48 6.58 90.06 OEA 13.29 5.48 85.89 8.34 94.23 EEA 13.48 5.01 79.49 12.91 92.41 REA 17.29 1.80 78.14 19.60 97.74 HEA 16.80 1.25 78.28 20.11 98.39 The FTIR spectra for estolide ethanolamides, as shown in Fig. 1 (c), illustrate the distinct absorbance peaks at 1640–1646 cm -1 (C = O stretching for carboxyl, amide), 1545–1550 cm -1 (N-O stretching, amide), and 3290–3305 cm -1 (N-H stretching, amide), confirming the formation of amide bonds. Further, the presence of strong absorbance peaks at 1730–1740 cm -1 (C = O stretching for carboxyl, ester) and 1050–1070 cm -1 (C-O stretching, ester) confirmed that the estolide linkages were retained. Similar to the 1 H-NMR spectra of estolides, the estolide amide spectra (Table 4 ) showed chemical shifts at 2.19–2.20 and 4.83–4.87 ppm corresponding to α-methylene ester and ester methine protons, respectively. For all the synthesized molecules, a distinct chemical shift at 2.26–2.28 ppm combined with low AV, confirmed the formation amide bond. Interestingly, another peak at 2.51 ppm was observed for undecylenic estolide amide (UEA). This peculiar peak observed could be correlated with the bond migration during the formation of estolides, combined with the lower chain length of UA, leading to a methylene group closer to an estolide linkage as well as an amide bond. This substantiates the highly branched structure of UE and UEA in comparison to the other molecules under study. Further, a peak at 3.7–3.73 ppm associated with the protons linked to carbon adjacent to the hydroxyl group was observed for all the estolide amides, implying a free alcohol group in the ethanolamine moiety, validating the selectivity of the reaction towards formation of amides. Table 5 1 H-NMR spectra for estolide amides Component Chemical Shift Integral UEA OEA EEA REA HEA -CH 3 0.87–0.89 6.00 6.00 6.00 6.00 6.00 -CH 2 - 1.18–2.03 57.11 53.30 78.60 44.58 63.44 –CH 2 –(C = O)–O–CH 2 – (α-methylene ester) 2.19–2.20 4.13 2.95 2.38 3.25 2.22 –CH 2 –(C = O)–OH (α-methylene amide) 2.26–2.28 4.68 1.84 1.97 3.49 2.09 –CH 2 –(C = O)–O–CH 2 – (α-methylene amide) 2.51 7.54 - - - - -NH-CH 2 - 3.41–3.42 4.28 2.12 2.11 2.10 1.89 –CH 2 –(HC-OH)–CH 2 – 3.57–3.62 - - - 0.88 0.96 -CH-OH 3.7–3.73 4.02 2.20 2.11 2.20 1.94 –CH 2 –(C = O)–O–CH 2 – (ester methine) 4.83–4.87 1.79 0.62 0.90 0.68 1.01 -CH = CH- (alkene) 5.38 1.35 1.42 1.07 2.78 0.00 -N-H 5.94–6.06 1.46 0.75 0.99 1.15 0.93 3.3. Pendulum tribometer experiments 3.3.1. System damping experiments The system damping experiments were conducted to assess the energy loss due to friction at bearings, air resistance, and material damping. A gradual non-linear decay in the oscillation, as shown in Fig. 3 (a), was observed with a damping time of approximately 6300 seconds. To take into consideration the viscous drag experienced by the sample disc, the system damping experiments were repeated with the sample plate submerged in the lubricant (similar to the configuration during sliding experiments) at temperatures of 40, 70, and 100˚C. But in comparison to the frictional loss at bearing contact and the air drag, the energy loss due to the viscous drag was found to be negligible, as seen in Fig. 3 (b, c, d). Owing to the long damping time of the pendulum, the energy loss per cycle due to the pendulum is very low. But to determine the precise energy dissipation at the tribo-contact during the sliding experiments, the energy dissipation of the pendulum at the no-load condition was subtracted from the total energy dissipation during the sliding experiment (per cycle). 3.3.2. Sliding experiments The disc samples and the lubricants were prepared as mentioned in section 2.6.1. All the fatty acids and the synthesised molecules were blended in the base oil. Hereafter, the acronym for each additive will be used to refer to its corresponding blend. The sliding experiments were carried out as per the methodology described in section 2.6.2. After the run-in, data from the optical encoder for angular displacement were recorded over a period of time. Figure 4 illustrates the damping curves for certain lubricant blends. It can be observed that for the base oil and EE at 100˚C, the damping time is slightly higher than 100 and 150 seconds, respectively, while for the UEA, it lies between 100 to 150 seconds. In comparison to the 6300 seconds of system damping experiments, the sliding experiments exhibited low damping times. This means that the energy dissipation at the tribo-contact is significantly higher than the other energy losses. Table 6 Damping Performance of Lubricants Sample Number of cycles (15˚ − 0.5˚) 40˚C 70˚C 100˚C Base Oil 69.33 ± 0.58 66.67 ± 1.15 58.00 ± 2.00 UA 83.00 ± 2.65 70.00 ± 2.65 64.67 ± 2.52 UE 74.00 ± 0.00 73.33 ± 0.58 72.00 ± 2.00 UEA 77.67 ± 1.15 67.33 ± 0.58 66.33 ± 0.58 OA 79.00 ± 1.00 75.33 ± 1.15 69.00 ± 0.00 OE 87.00 ± 1.00 78.33 ± 1.53 80.33 ± 1.15 OEA 83.00 ± 1.00 79.67 ± 2.31 68.33 ± 1.53 EA 90.33 ± 1.15 91.67 ± 2.08 87.33 ± 1.53 EE 90.67 ± 2.89 88.67 ± 1.15 91.33 ± 2.08 EEA 84.67 ± 3.06 87.00 ± 2.65 79.67 ± 0.58 RA 77.67 ± 0.58 77.67 ± 2.52 74.00 ± 1.00 RE 74.67 ± 1.53 71.33 ± 0.58 74.00 ± 2.65 REA 68.00 ± 2.65 72.33 ± 0.58 69.00 ± 1.00 HE 87.00 ± 1.00 88.00 ± 1.73 89.33 ± 0.58 HEA 83.00 ± 2.00 76.00 ± 1.00 85.67 ± 1.15 Overall % relative standard deviation 1.86 The relative performance of the lubricants can be determined from the oscillation decay of a pendulum, specifically by counting the number of cycles until the motion ceases. Higher decay time implied lower energy dissipation per cycle, which meant lower COF. The number of cycles for the pendulum to decay from 15 ˚ to 0.5˚ for all the evaluated lubricants has been reported in Table 6 . It was observed that all the synthesised additives (except for REA at 40˚C) showed a higher number of cycles than the base oil, suggesting their ability as OFMs. The % relative standard deviation was as low as 1.86, validating the exceptional repeatability of the experiments. EE at 40˚C, EA at 70˚C, and EE at 100˚C were found to have the highest number of cycles, indicating lower COF. But the number of cycles cannot be used to compare quantitative values of COF. The underlying reason is the change in COF with sliding velocity, as established by the Stribeck equation [ 54 ]. The average sliding velocity decreases with successive cycles, leading to a change in COF, whose magnitude could vary for different lubricants. This variation can be seen in Fig. 4 , wherein the rate of decay increased rapidly for base oil in comparison to the EE at lower amplitudes of oscillation, suggesting a rise in COF. Thus, it is crucial to determine the Stribeck Curves of the evaluated lubricants at such lower sliding velocities. 3.4. Evaluation of the coefficient of friction The coefficient of friction was calculated using the damping curves of the sliding and the system damping experiments as reported by Divakaran et al. [ 46 ]. Figures 5 , 6 , and 7 illustrate the COF for fatty acids, estolides, and estolide amides, respectively. Among the curves, many have a spike in COF at lower velocities (less than 2 mm/sec). This occurrence of a sudden increase in COF can probably be a result of the transition from sliding to stick-slip at lower velocities [ 55 ]. Also, it was observed that at low temperature, the COF curves were smooth, while at elevated temperature, noisy curves were obtained, especially for fatty acids and estolide amides. Various molecular properties of the OFMs, like the functional groups, molecular structure, packing efficiency, adsorption, and desorption, could lead to this variation [ 14 , 56 ] and thus need to be discussed in detail. 3.5. Molecular Structure of OFMs and Friction in the BL Table 7 depicts the physicochemical properties of the molecules in terms of their theoretical MW and experimental PP, and frictional values of their blends (averaged over the sliding velocity of 2 to 13 mm/sec; to eliminate the fluctuation due to stick-slip transition). Distinct, temperature-dependent performance was observed across the additive classes. At the lower and higher temperatures of 40°C and 100°C, the estolides exhibited superior frictional performance, achieving average reductions of 13.92% and 29.92%, respectively, relative to the base oil. In contrast, at the intermediate temperature of 70°C, the fatty acids were most effective, yielding an average friction reduction of 16.63%. While the estolide amides were less effective, a substantial lowering of friction was still recorded compared to the base oil. Notably, exceptional performance was demonstrated by EE, which emerged as the best OFM with a remarkable 36.91% reduction in COF at 100°C. Despite these additive class-specific trends, it is clear from Table 7 that significant performance variations exist within each group, emphasising the critical role of molecular structures in determining tribological efficacy. The fatty acids under study have subtle differences in molecular structure, wherein UA has terminal unsaturation. OA and EA have unsaturation within the chain, while RA has a hydroxyl group in addition to the unsaturation. Although not studied in this acid form, owing to its insolubility in the base oil, the hydroxystearic acid has a hydroxyl group with no unsaturation. The transformation of fatty acid to estolide is accompanied by an increase in molecular weight and a decrease in pour point (PP) [17–20]. This reduction in the PP is attributed to the introduction of branching, resulting in reduced packing efficiency [57, 58]. Further transformation from estolide to ethanolamide leads to a significant increase in the packing efficiency as reported in the literature [14, 59]. But the amides have a different polar head group than the fatty acids and estolides, having an amide bond and a free alcohol moiety. Table 7 : Physicochemical properties of synthesized OFMs and Frictional properties of their blends 3.5.1. Frictional Performance at 40˚C At 40˚C, the fatty acids, having higher packing efficiency (higher PP) were seen to have lower COF. Higher packing efficiency of the OFMs has been reported to form a stable adsorbed film providing enhanced protection, especially in the BL regime [ 5 , 60 , 61 ]. Similarly, the estolides and amides with comparatively higher packing were found to have lower friction. The friction reduction ability of UE in comparison to UA was drastically reduced, owing to the significant drop in the packing efficiency as a result of the highly branched molecular structure of UE [ 19 ]. Similarly, derivatives of RA exhibited poor frictional performance due to inadequate packing. Except for the poorly packed molecule (UE, UEA, RE & REA), the variation in friction, as a result of different molecular structures, was reduced in estolides and amides due to higher MW and van der Waals forces. Higher MW and van der Waals forces have been extensively reported to aid the formation of a robust and stronger adsorbed film on the metal surface, decreasing COF in BL regime [ 62 – 65 ]. 3.5.2. Frictional Performance at 70˚C Contrary to the trend observed at 40˚C, the magnitude of friction reduction at 70˚C showed a strong correlation with molecular weight, a relationship that was particularly pronounced for fatty acids. At elevated temperatures, the limiting factor for the stability of the adsorbed film is the rate of desorption, which is higher for molecules with lower MWs [ 59 ]. For fatty acids, estolides as well as amides, the friction was observed to decrease with the MW as we compare the undecylenic, oleic, and erucic derivatives counterparts, establishing a critical role of MW. Except for RE and HEA, the larger molecules within the group, like EA, RA, EE, HE, EEA, REA, showed enhanced frictional response during sliding at 70˚C than at 40˚C, confirming the critical role of MW at elevated temperature. In addition, poor packing of the adsorbed film, correlated by lower PP, was seen to decrease the additive efficacy as observed for undecylenic and ricinoleic derivatives. An additional factor contributing to the improved frictional performance is the chemisorption of the adsorbed molecules to form metal oxide soaps [ 5 , 46 , 66 ]. The extent of this improvement is governed by both the probability of chemisorption and the requisite activation energy [ 66 ]. The probability, in turn, depends on the stability of the initial physisorbed film, which is inversely related to the rate of desorption [ 59 , 63 ]. The activation energy is a function of molecular complexity and molecular weight [ 67 ]. The reduction in the COF with increasing temperature (from 40°C to 70°C) was more significant for EA than for EE. This difference can be attributed to the higher activation energy expected for the estolide; owing to its sterically hindered carboxylic group and greater molecular weight, it requires more thermal energy to effectively transition from physisorption to chemisorption. For other molecules studied, this effect was less pronounced due to a complex interplay of factors, including molecular weight and packing efficiency, in addition to chemisorption [ 56 , 68 ]. 3.5.3. Frictional Performance at 100˚C The trend in the frictional values for sliding experiments at 100˚C varied from that at 40˚C and 70˚C. For all the fatty acids, the COF was higher and correlated inversely with the MW of the molecules. Although at 100˚C, the molecules had substantial energy to undergo chemisorption, the higher desorption rates limited the probability of chemisorption [ 59 ], leading to poor fractional performance. On the other hand, the estolides, owing to their higher MW and thus lower desorption rates, had a higher probability of chemisorption, leading to a lower COF at 100˚C. Unlike fatty acids, the effect of packing efficiency was significant for estolides even at the elevated temperature, as the COF of RE was observed to be higher than OE, despite the higher MW of the former. In the case of amides (except for HEA), despite their higher MW, the friction was higher at 100˚C due to the inability of the -OH head group to undergo chemisorption. Interestingly, the performance of large molecules of amides was observed to be inferior to their significantly smaller fatty acid counterparts, signifying the importance of the ability to chemisorb at elevated temperatures. 4. Conclusion Estolide and Estolide ethanolamide derivatives of fatty acids, including undecylenic, oleic, erucic, ricinoleic, and hydroxystearic acids, were synthesised and characterised using FTIR and 1 H-NMR. The fatty acids and the synthesised OFMs were evaluated for their ability to reduce friction in the boundary lubrication regime using a custom-built FCPeT. The experiments were found to be repeatable with friction reductions in the range of 10–30%. This study established the role of molecular structure, characterised by the functional group, branching, and molecular weight, in the variation of the COF at different temperatures. Transformation to estolides improves the frictional performance, especially at elevated temperatures of 100˚C. Estolide ethanolamide, owing to its inability to chemisorb, illustrated inferior performance to the fatty acids and estolides. EA, EE, and EEA consistently demonstrated the lowest performance within their respective classes across the entire temperature range studied, emphasizing the impact of higher molecular weight and relatively lower branching in achieving optimal OFM performance. Statements & Declarations Funding This work was supported by the Department of Science and Technology, India, through its INSPIRE Fellowship program. Competing Interests The authors have no relevant financial or non-financial interests to disclose. Author Contributions All authors contributed to the study conception and design. Material preparation was performed by Prasad Sanap, Somesh Patil, Bhagesh Kori, Nidhi Jain, Rakshit Sinha and Viraj Tungare. Data collection and analysis were performed by Prasad Sanap and Vikas Kumar Singh. The first draft of the manuscript was written by Prasad Sanap and Vikas Kumar Singh. 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10:51:03","extension":"xml","order_by":19,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":184483,"visible":true,"origin":"","legend":"","description":"","filename":"8eaa9dbabe714c00b841edb7afd365d11structuring.xml","url":"https://assets-eu.researchsquare.com/files/rs-7921826/v1/aec6e7dbc2f91211a46771b8.xml"},{"id":95822671,"identity":"f0f14e6e-d985-4f28-9369-0e0d578cf5f8","added_by":"auto","created_at":"2025-11-13 10:51:03","extension":"html","order_by":20,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":197091,"visible":true,"origin":"","legend":"","description":"","filename":"earlyproof.html","url":"https://assets-eu.researchsquare.com/files/rs-7921826/v1/fe10642f1db004ae663094eb.html"},{"id":95822642,"identity":"a30b6cd0-a3d4-4ffe-914c-87db6e570994","added_by":"auto","created_at":"2025-11-13 10:51:02","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":32380,"visible":true,"origin":"","legend":"\u003cp\u003eSchematic of Force Controlled Pendulum Tribometer\u003c/p\u003e","description":"","filename":"1.png","url":"https://assets-eu.researchsquare.com/files/rs-7921826/v1/2ce415a2f9e5fd802b5690da.png"},{"id":95822641,"identity":"72fde435-4581-4934-8d63-336c5f4a035f","added_by":"auto","created_at":"2025-11-13 10:51:02","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":103368,"visible":true,"origin":"","legend":"\u003cp\u003eFTIR Spectra (a) Acids (b) Estolides (c) Estolide Amides\u003c/p\u003e","description":"","filename":"2.png","url":"https://assets-eu.researchsquare.com/files/rs-7921826/v1/dcf0a5b13e7d1ffaa0e869be.png"},{"id":95822644,"identity":"add7bc99-0d86-4a77-91dd-2d532200b98a","added_by":"auto","created_at":"2025-11-13 10:51:02","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":58883,"visible":true,"origin":"","legend":"\u003cp\u003eDamping curve for system damping experiments (a) no lubricant (b) base oil at 40˚C (c) base oil at 70˚C (d) base oil at 100˚C\u003c/p\u003e","description":"","filename":"3.png","url":"https://assets-eu.researchsquare.com/files/rs-7921826/v1/136c54520f4db57f3df31d30.png"},{"id":96240358,"identity":"8270d7b4-03d5-44d2-9d04-d363c3758c41","added_by":"auto","created_at":"2025-11-19 07:08:51","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":48889,"visible":true,"origin":"","legend":"\u003cp\u003eDamping curve for sliding experiments (a) base oil at 100˚C (b) 0.1% UEA in base oil at 100˚C (c) 0.1% EE in base oil at 100˚C\u003c/p\u003e","description":"","filename":"4.png","url":"https://assets-eu.researchsquare.com/files/rs-7921826/v1/c3e994840661c5979c98b943.png"},{"id":96239171,"identity":"52736b2e-6cec-47ac-a1ea-eef8f49d0ad4","added_by":"auto","created_at":"2025-11-19 07:04:23","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":127226,"visible":true,"origin":"","legend":"\u003cp\u003eStribeck curves for fatty acids (a) sliding at 40˚C (b) sliding at 70˚C (c) sliding at 100˚C\u003c/p\u003e","description":"","filename":"5.png","url":"https://assets-eu.researchsquare.com/files/rs-7921826/v1/2e576529631e05b364fa32eb.png"},{"id":95822652,"identity":"8286be90-69eb-4e14-ad5c-76d1c1f6b954","added_by":"auto","created_at":"2025-11-13 10:51:02","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":137636,"visible":true,"origin":"","legend":"\u003cp\u003eStribeck curves for estolide (a) sliding at 40˚C (b) sliding at 70˚C (c) sliding at 100˚C\u003c/p\u003e","description":"","filename":"6.png","url":"https://assets-eu.researchsquare.com/files/rs-7921826/v1/e0b8808b617653f4135e819f.png"},{"id":95822643,"identity":"46048556-4bef-47bd-8e6a-85730f16042a","added_by":"auto","created_at":"2025-11-13 10:51:02","extension":"png","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":149495,"visible":true,"origin":"","legend":"\u003cp\u003eStribeck curves for estolide amide (a) sliding at 40˚C (b) sliding at 70˚C (c) sliding at 100˚C\u003c/p\u003e","description":"","filename":"7.png","url":"https://assets-eu.researchsquare.com/files/rs-7921826/v1/ba5d8bb163bbec6c27f51b4d.png"},{"id":97668720,"identity":"0b2e21c5-5e1a-4bb8-a456-99821212f0cd","added_by":"auto","created_at":"2025-12-08 09:26:09","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":1744615,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-7921826/v1/e584e52e-8007-4a68-9a7b-50336da38b0c.pdf"},{"id":96239185,"identity":"4433d67a-3c82-47b4-8160-f4774b92720f","added_by":"auto","created_at":"2025-11-19 07:04:43","extension":"docx","order_by":1,"title":"","display":"","copyAsset":false,"role":"supplement","size":146680,"visible":true,"origin":"","legend":"","description":"","filename":"GraphicalAbstract.docx","url":"https://assets-eu.researchsquare.com/files/rs-7921826/v1/4eb5bf5c73f760cc6a2b8516.docx"}],"financialInterests":"No competing interests reported.","formattedTitle":"Boundary lubrication performance of fatty acid and its derivatives using energy dissipation method","fulltext":[{"header":"1. Introduction","content":"\u003cp\u003eBoundary lubrication (BL) illustrates a critical regime where the surface asperities primarily carry the load between two contacting surfaces. The characteristic features that lead to BL are low speeds and higher loads. These conditions can lead to excessive heat, wear, and potential seizure. To mitigate the high friction and wear, OFMs are added to the lubricants. These OFMs have an affinity towards the metal substrates, thus adsorb on the surface and form a protective film that lowers the direct metal-to-metal contact while dissipating the shear forces [\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e]. OFMs are amphiphilic molecules possessing a polar head group and a long hydrocarbon chain. The effectiveness of OFMs is influenced by molecular structure in terms of the functional groups, packing efficiency, and their molecular weights [\u003cspan additionalcitationids=\"CR3 CR4 CR5 CR6 CR7 CR8 CR9\" citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e]. The most prominent functional groups reported are carboxylic acids, alcohols, esters, amines, amides, and ethanolamides [\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e, \u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e, \u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e]. Fatty acids are the most effective OFMs wherein their carboxyl head group forms strong chemisorptive bonds with metal oxides [\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e, \u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e]. Similar chemisorbed bonds with metal oxides are formed by amide-based OFMs [\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e]. While the hydroxyl group of alcohols forms hydrogen bonds with metal oxide surfaces, the overall adsorption is weaker than acids and amides [\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e, \u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e]. On the other hand, the ethanolamide-based OFMs have enhanced adsorption due to hydrogen bonding of the hydroxyl group along with chemical interaction of the amide moieties [\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e]. Also, esters are used owing to their ability to adsorb on metal surfaces and provide excellent film coverage [\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e]. Quite recently, a new class of polymeric friction modifiers has been evaluated as OFMs. These molecules consist of multiple polar groups across a high molecular weight chain, leading to multivalent adsorption capabilities [\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e, \u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e].\u003c/p\u003e\u003cp\u003eFatty acids having either unsaturation or hydroxy groups can be oligomerized into Estolides by the formation of secondary ester linkages while preserving a carboxyl moiety [\u003cspan additionalcitationids=\"CR18 CR19 CR20 CR21 CR22 CR23\" citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e]. Conventionally, estolides derived from oleic acid and ricinoleic acid have been extensively studied for their potential utility in lubricants [\u003cspan additionalcitationids=\"CR26 CR27 CR28 CR29 CR30 CR31 CR32\" citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e33\u003c/span\u003e]. Recently, estolides derived from undecylenic acid and 12-hydroxystearic acid have been studied for their tribological properties [\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e, \u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e, \u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e]. But there is scarce literature regarding estolides derived from erucic acid [\u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e34\u003c/span\u003e]. Essentially, the formation of estolides is accompanied by a reduction in unsaturation or hydroxyl group (as relevant to the chemistry) and an increase in molecular weight as well as branching. Estolides have been reported to form protective layers due to their polarity and branched ester linkages. Moreover, the steric hindrances and higher molecular weight aid in lubricant integrity under mechanical stress [\u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e35\u003c/span\u003e]. Thus, this reduction in unsaturation, increased branching, and molecular weight has been reported to improve the lubricity, especially in the BL regime [\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e, \u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e, \u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e36\u003c/span\u003e].\u003c/p\u003e\u003cp\u003eOwing to the free carboxyl moiety, estolides can be further derivatized to various molecules, including esters, soaps, and amides. Although extensive studies of estolide esters [\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e, \u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e, \u003cspan citationid=\"CR44\" class=\"CitationRef\"\u003e44\u003c/span\u003e, \u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e, \u003cspan additionalcitationids=\"CR38 CR39 CR40 CR41 CR42\" citationid=\"CR37\" class=\"CitationRef\"\u003e37\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR43\" class=\"CitationRef\"\u003e43\u003c/span\u003e] and a few studies related to estolide soaps [\u003cspan citationid=\"CR45\" class=\"CitationRef\"\u003e45\u003c/span\u003e] have been reported, the amide derivatives of estolides have not been explored. The dual activity of the ethanolamides, combined with the polymeric structure of estolides, could potentially aid friction modification in BL and thus needs to be studied.\u003c/p\u003e\u003cp\u003eThe boundary lubrication (BL) regime requires precise study since asperities interact directly. Conventional tribometers face limitations in replicating real tribo-contacts, as motors and direct-contact sensors can alter true interface conditions. Moreover, the BL regime is highly sensitive to the mode of motion, force-controlled or displacement-controlled, during sliding. Lubricant performance in this regime is better captured under force-controlled motion [\u003cspan citationid=\"CR46\" class=\"CitationRef\"\u003e46\u003c/span\u003e]. To address these challenges, a custom-built FCPeT was employed in the present study [\u003cspan citationid=\"CR46\" class=\"CitationRef\"\u003e46\u003c/span\u003e]. In the current study, estolides of undecylenic, oleic, erucic, ricinoleic, and 12-hydroxystearic acid were synthesized and further derivatized to monoethanolamides. The fatty acids and their respective estolides and estolide monoethanolamides were then evaluated as friction modifiers in the BL regime at a 1000 ppm dosage level in group III base oil. The frictional evaluation was carried out at 40˚C, 70˚C, and 100˚C with the aid of FCPeT using the energy dissipation method.\u003c/p\u003e"},{"header":"2. Materials and Methods","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e\u003ch2\u003e2.1. Materials\u003c/h2\u003e\u003cp\u003eOleic acid (75%) and erucic acid (90%) were obtained as samples from Godrej Industries Ltd. Ricinoleic acid and 12-hydroxystearic acid were obtained as samples from Gokul Agro Resources Ltd. Undecylenic acid was procured from Prime Chemicals, Karnataka. Sulfuric acid (CAS No. 7664-93-9), ethanolamine (CAS No. 141-43-5), and sodium methoxide (CAS No. 124-41-4) were procured from SD Fine Chemicals. SN 150 (group 2, ISO VG 32) base oil was procured from BSM Lubricants. Hexane, ethanol, and other solvents used were of commercial grades.\u003c/p\u003e\u003cp\u003eFor the frictional study, an EN 31 steel block (42.5 \u0026times; 30 \u0026times; 15 mm) was utilized as a disc after surface finishing as described in section 2.6.1. A high-carbon chromium steel pin with a radius of 6 mm and surface roughness of 90 nm was utilized as the counter-surface.\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec4\" class=\"Section2\"\u003e\u003ch2\u003e2.2. Synthesis of unsaturated fatty acid estolides\u003c/h2\u003e\u003cp\u003eUnsaturated fatty acid (undecylenic acid/ oleic acid/ erucic acid) and sulfuric acid (0.6 mole equivalent) were added to a flask. The mixture was agitated at 300\u0026ndash;400 rpm using an overhead stirrer at 50˚C for 4 hours. The reaction was carried out under the influence of 25 kHz (225W) ultrasonication provided through a water bath. After the completion of the time period, the reaction mixture was transferred to a separation funnel, and hexane was added. The organic layer was given multiple hot brine washings to remove the acidic catalyst. The organic layer was dried over an anhydrous sodium sulfate bed, and the solvent was removed using a rotatory evaporator to get estolides.\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec5\" class=\"Section2\"\u003e\u003ch2\u003e2.3. Synthesis of hydroxy fatty acid estolides\u003c/h2\u003e\u003cp\u003eHydroxy fatty acids (ricinoleic acid/ 12-hydroxystearic acid) were added to a flask, heated to a temperature of 180˚C, and agitated at 300\u0026ndash;400 rpm using an overhead stirrer for 8 hours. A Dean and Stark apparatus was used to remove the water of reaction with the aid of a vacuum (500\u0026ndash;600 mm Hg). After 8 hours, estolide with desired oligomerization was obtained and used for further analysis.\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec6\" class=\"Section2\"\u003e\u003ch2\u003e2.4. Synthesis of estolide ethanolamides\u003c/h2\u003e\u003cp\u003eEstolide and ethanolamine (1:1.1 mol) were added to a flask and heated to 180˚C under constant agitation of 300\u0026ndash;400 rpm using an overhead stirrer. Sodium methoxide (0.1%) was used as a catalyst for the reaction. A Dean and Stark apparatus was used to remove the water of reaction. The reaction was carried out for 8 hours, and at the end of the reaction vacuum (500\u0026ndash;600 mm Hg) was utilized to remove the excess of ethanolamine added to the reaction. After cooling, estolide ethanolamides were obtained.\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec7\" class=\"Section2\"\u003e\u003ch2\u003e2.5. Instrumental characterization\u003c/h2\u003e\u003cp\u003eThe structure of estolides and ethanolamides was confirmed with the aid of FTIR spectra obtained using a PerkinElmer 100-FTIR Spectrometer over a wavelength range of 650 to 4000 cm\u003csup\u003e-1\u003c/sup\u003e and NMR spectra using an Agilent ProPulse at 500 MHz using CDCl\u003csub\u003e3\u003c/sub\u003e as a solvent.\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec8\" class=\"Section2\"\u003e\u003ch2\u003e2.6. Forced Controlled Pendulum Tribometer (FCPeT)\u003c/h2\u003e\u003cp\u003eAs shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e, FCPeT was employed to evaluate the energy efficiency of synthesized friction modifiers in the boundary lubrication (BL) regime. The FCPeT consists of a pendulum mounted on a horizontal shaft supported by ball bearings. One end of the shaft holds the test sample, while the opposite end is connected to a high-resolution rotary encoder (0.000219\u0026deg;), which precisely records the pendulum\u0026rsquo;s angular position.\u003c/p\u003e\u003cp\u003eA pulley\u0026ndash;mass-based load assembly applies a controlled normal force at the tribo-contact, ensuring accurate loading conditions. The pendulum is displaced by a known angle to introduce potential energy, which is subsequently dissipated by the system during oscillation.\u003c/p\u003e\u003cp\u003eTo differentiate the energy loss due to tribo-contact friction from other system losses, a two-step baseline correction procedure was employed:\u003c/p\u003e\u003cp\u003e\u003col\u003e\u003cspan\u003e\u003cli\u003e\u003cp\u003eSystem damping experiment: The tribo-contact was kept apart (no sliding) while the sample was immersed in lubricant, and the decay response of the pendulum was recorded. This measured the dissipation of energy solely due to system damping.\u003c/p\u003e\u003c/li\u003e\u003c/span\u003e\u003cspan\u003e\u003cli\u003e\u003cp\u003eSliding experiment: The tribo-contact was engaged, and the pendulum damping was recorded again. This included the combined effects of system damping and tribo-contact friction.\u003c/p\u003e\u003c/li\u003e\u003c/span\u003e\u003c/ol\u003e\u003c/p\u003e\u003cp\u003eBy subtracting the first case (system damping) from the second (system damping\u0026thinsp;+\u0026thinsp;tribo-contact), the net energy dissipation due to tribo-contact friction was isolated. This correction accounted for bearing friction, system damping, air drag on the pendulum shaft, and viscous drag from the base oil.\u003c/p\u003e\u003cp\u003eThe frictional loss per cycle was calculated from the reduction in potential energy (amplitude decay) of the pendulum swing. Normalizing this loss with the sliding distance per cycle yielded the frictional loss per unit distance. The coefficient of friction (COF) was then obtained by dividing this value by the applied normal load and plotted as a function of average sliding velocity. A more detailed description of this methodology is provided by Divarakan et al. [\u003cspan citationid=\"CR46\" class=\"CitationRef\"\u003e46\u003c/span\u003e].\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cdiv id=\"Sec9\" class=\"Section3\"\u003e\u003ch2\u003e2.6.1. Preparation of Lubricant and Disc Samples\u003c/h2\u003e\u003cp\u003eThe fatty acids, estolides, and estolide amide derivatives were blended in VG 32 group III base oil at a dosage level of 0.1% w/w. The blending was carried out at an elevated temperature of around 60\u0026ndash;70˚C under constant agitation till the OFMs were dissolved to homogeneity. For tribo-contact, a flat EN 31 steel plate was utilized, considering its wide use in machinery tribo-contacts. To achieve consistent surface topography, the flat samples were prepared by polishing using a progression of emery sheets from coarser 220 to a mirror finish grit size of 4000. The polishing process involved 50 unidirectional sliding passes for each emery sheet sequentially in order of 220, 320, 400, 800, 1000, 1200, 1500, 2000, 2500, 3000, and 4000. For the counter surface, a 6 mm diameter high-carbon chromium steel ball was utilized. Before initiating the experiment, the plate and ball were thoroughly cleaned with hexane to eliminate the impurities present on the surface.\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec10\" class=\"Section3\"\u003e\u003ch2\u003e2.6.2. Experiments using FCPeT\u003c/h2\u003e\u003cp\u003e\u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab1\" border=\"1\"\u003e\u003ccaption language=\"En\"\u003e\u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e\u003cdiv class=\"CaptionContent\"\u003e\u003cp\u003eExperimental Configuration\u003c/p\u003e\u003c/div\u003e\u003c/caption\u003e\u003ccolgroup cols=\"2\"\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e\u003cthead\u003e\u003ctr\u003e\u003cth align=\"left\" colname=\"c1\"\u003e\u003cp\u003eTesting parameters\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c2\"\u003e\u003cp\u003eValue\u003c/p\u003e\u003c/th\u003e\u003c/tr\u003e\u003c/thead\u003e\u003ctbody\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eRunning-in\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e10 repetitions (20˚ to 15˚)\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eNormal load\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:1\\:N\\)\u003c/span\u003e\u003c/span\u003e\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eRelease angle\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e15˚\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eAngular resolution\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e0.000219\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:^\\circ\\:\\)\u003c/span\u003e\u003c/span\u003e\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eDAQ (Angular position of the pendulum)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:100\\:kHz\\)\u003c/span\u003e\u003c/span\u003e\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eMaximum sliding velocity\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:13\\:mm/s\\)\u003c/span\u003e\u003c/span\u003e\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eLubricant Temperature\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e40, 70 \u0026amp; 100˚C\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003c/tbody\u003e\u003c/colgroup\u003e\u003c/table\u003e\u003c/div\u003e\u003c/p\u003e\u003cp\u003eThe experiments were carried out as per the experimental setup, as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e, using the configuration provided in Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e. For system damping experiments, the pendulum was released from an angle of 15˚, and the damping of the pendulum was recorded using the optical encoder. Similar system damping experiments were carried out submerging the disc samples in the base oil at temperatures of 40, 70, and 100˚C, respectively. No normal load was applied during these experiments. For sliding experiments, the lubricant was first heated to the desired temperature. The normal load of 10 N, equivalent to 0.9 GPa maximum contact pressure, was applied to the disc using the pulley mechanism. Before initiating measurements, the contact surfaces were run in by oscillating the pendulum 10 times from an initial angle of 20˚ to 15˚ to ensure a steady state during measurement. Following the run-in period, each experimental trial was initiated by releasing the pendulum from an initial angle of 15˚. The subsequent angular position was recorded at a sampling rate of 100 kHz until the pendulum came to a complete rest. For each lubricant at a specific temperature, the experiment was repeated in triplicate to ensure repeatability. The recorded angular displacement with time was then utilized to determine the COF using the energy dissipation method as reported by Divakaran et al. [\u003cspan citationid=\"CR46\" class=\"CitationRef\"\u003e46\u003c/span\u003e]. For the calculation, a single cycle was considered. The energy loss over the cycle was determined using the change in potential energy (decrease in amplitude). The energy loss due to the other factors, as determined by system damping experiments, for an equivalent amplitude of cycle, was subtracted to get the energy loss at the tribo-contact. The distance covered by the pin over the plate during the cycle was calculated using the angular displacement data and the radius (15 mm from the axis). The calculated frictional loss for the cycle was divided by the applied normal load (10N) and the sliding distance to get the COF. The COF calculated for different cycles for each lubricant from 15˚ till the motion of the pendulum ceases was plotted against the average sliding velocity (calculated using the derivative of the damping curve).\u003c/p\u003e\u003c/div\u003e\u003c/div\u003e"},{"header":"3. Results and Discussion","content":"\u003cdiv id=\"Sec12\" class=\"Section2\"\u003e\n \u003ch2\u003e3.1. Synthesis of estolides\u003c/h2\u003e\n \u003cdiv class=\"gridtable\"\u003e\n \u003ctable id=\"Tab2\" border=\"1\"\u003e\n \u003ccaption language=\"En\"\u003e\n \u003cdiv class=\"CaptionNumber\"\u003eTable 2\u003c/div\u003e\n \u003cdiv class=\"CaptionContent\"\u003e\n \u003cp\u003e\u003csup\u003e1\u003c/sup\u003eH-NMR spectra for estolides\u003c/p\u003e\n \u003c/div\u003e\n \u003c/caption\u003e\n \u003cthead\u003e\n \u003ctr\u003e\n \u003cth align=\"left\" rowspan=\"2\"\u003e\n \u003cp\u003eComponent\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\" rowspan=\"2\"\u003e\n \u003cp\u003eChemical Shift\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\" colspan=\"5\"\u003e\n \u003cp\u003eIntegral\u003c/p\u003e\n \u003c/th\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eUE\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eOE\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eEE\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eRE\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eHE\u003c/p\u003e\n \u003c/th\u003e\n \u003c/tr\u003e\n \u003c/thead\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e-CH\u003csub\u003e3\u003c/sub\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.87\u0026ndash;0.89\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e6.00\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e6.00\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e6.00\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e6.00\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e6.00\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e-CH\u003csub\u003e2\u003c/sub\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e1.18\u0026ndash;2.02\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e43.14\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e46.59\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e64.63\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e45.66\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e57.75\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u0026ndash;CH\u003csub\u003e2\u003c/sub\u003e\u0026ndash;(C\u0026thinsp;=\u0026thinsp;O)\u0026ndash;O\u0026ndash;CH\u003csub\u003e2\u003c/sub\u003e\u0026ndash;\u003c/p\u003e\n \u003cp\u003e(\u0026alpha;-methylene ester)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e2.26\u0026ndash;2.27\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e3.41\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e1.62\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e2.11\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e3.60\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e2.25\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u0026ndash;CH\u003csub\u003e2\u003c/sub\u003e\u0026ndash;(C\u0026thinsp;=\u0026thinsp;O)\u0026ndash;OH\u003c/p\u003e\n \u003cp\u003e(\u0026alpha;-methylene acid)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e2.34\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e2.59\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e2.22\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e2.11\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e3.60\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e1.88\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u0026ndash;CH\u003csub\u003e2\u003c/sub\u003e\u0026ndash;(HC-OH)\u0026ndash;CH\u003csub\u003e2\u003c/sub\u003e\u0026ndash;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e3.59\u0026ndash;3.62\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.44\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.75\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u0026ndash;CH\u003csub\u003e2\u003c/sub\u003e\u0026ndash;(C\u0026thinsp;=\u0026thinsp;O)\u0026ndash;O\u0026ndash;CH\u003csub\u003e2\u003c/sub\u003e\u0026ndash;\u003c/p\u003e\n \u003cp\u003e(ester methine)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e4.83\u0026ndash;4.87\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e1.46\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.71\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.95\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e1.02\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e1.13\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e-CH\u0026thinsp;=\u0026thinsp;CH-\u003c/p\u003e\n \u003cp\u003e(alkene)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e5.37\u0026ndash;5.38\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.65\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e1.06\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e1.05\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e1.76\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n \u003c/table\u003e\n \u003c/div\u003e\n \u003cp\u003esynthesizedbased on undecylenic (UA), oleic (OA), and erucic acid (EA) were synthesized with the aid of ultrasonication under the catalytic activity of sulfuric acid as per the method mentioned in section 2.2 [\u003cspan class=\"CitationRef\"\u003e20\u003c/span\u003e, \u003cspan class=\"CitationRef\"\u003e47\u003c/span\u003e]. While estolides based on ricinoleic acid (RA) and 12-hydroxystearic acid (HA) were synthesised by homo-polymerization at elevated temperatures without the use of any catalyst [\u003cspan class=\"CitationRef\"\u003e21\u003c/span\u003e]. The formation of estolides was confirmed with the aid of \u003csup\u003e1\u003c/sup\u003eH-NMR (Table \u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003e) and FTIR (Fig. \u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003e). For \u003csup\u003e1\u003c/sup\u003eH-NMR spectra of all the estolides, two distinct chemical shifts in the range of 2.20\u0026ndash;2.40 ppm confirmed the formation of the ester linkage (2.26\u0026ndash;2.27 ppm) along with unreacted carboxylic acid (2.34 ppm). Moreover, the peak associated with ester methine in the range of 4.86\u0026ndash;4.87 ppm confirmed the formation of estolide. The disappearance of the peak related to terminal unsaturation of UA can be linked with the bond migration during estolide formation [\u003cspan class=\"CitationRef\"\u003e19\u003c/span\u003e]. Also, the FTIR spectra {Figure \u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003e (a) \u0026amp; (b)} illustrate the shift in absorbance from 1700\u0026ndash;1710 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e (C\u0026thinsp;=\u0026thinsp;O stretching for carboxyl, acid) to 1730\u0026ndash;1740 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e (C\u0026thinsp;=\u0026thinsp;O stretching for carboxyl, ester) linked to the formation of estolide linkages. Also, absorbance at 1175\u0026ndash;1180 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e (C-O stretching, ester) confirmed the formation of estolide. The sharp peak 909 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e (C\u0026thinsp;=\u0026thinsp;C bending) associated with unsaturation observed in the case of undecylenic acid disappeared in the case of undecylenic estolide (UE), confirming the reduction in unsaturation as a result of estolide formation. Similarly, the disappearance of the peak associated with unsaturation was observed by oleic (OE) and erucic estolides (EE) in comparison to their acid counterparts.\u003c/p\u003e\n \u003cp\u003eSince the polymerisation reaction associated with the formation of estolides yields a mixture of monomer, dimer, and higher oligomers, the synthesised estolides were characterised by their average estolide number (EN), as determined using the Acid Value (AV) and \u0026sup1;H-NMR [\u003cspan class=\"CitationRef\"\u003e19\u003c/span\u003e\u0026ndash;\u003cspan class=\"CitationRef\"\u003e21\u003c/span\u003e, \u003cspan class=\"CitationRef\"\u003e48\u003c/span\u003e]. The average estolide number is as mentioned in Table \u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003e. Except for UE and OE, the EN for estolides is around 2, which correlates to the formation of dimeric molecules. In the case of OE, the lower oleic content (around 75%) led to the formation of estolide with slightly lower EN. While in the case of UE, the lower molecular weight (MW) of undecylenic acid led to faster reaction, leading to an estolide with higher EN. The Average EN was then used to determine the average MW of the synthesised estolides (MW\u0026thinsp;=\u0026thinsp;56100/AV\u0026nbsp;\u003csub\u003eAverage EN\u003c/sub\u003e).\u003c/p\u003e\n \u003cdiv class=\"gridtable\"\u003e\n \u003ctable id=\"Tab3\" border=\"1\"\u003e\n \u003ccaption language=\"En\"\u003e\n \u003cdiv class=\"CaptionNumber\"\u003eTable 3\u003c/div\u003e\n \u003cdiv class=\"CaptionContent\"\u003e\n \u003cp\u003eEstolide number and molecular weight of synthesised estolides\u003c/p\u003e\n \u003c/div\u003e\n \u003c/caption\u003e\n \u003cthead\u003e\n \u003ctr\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eSample\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eAcid Value (mg KOH/g)\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eEN* using the Acid Value Method\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eEN* using the \u0026sup1;H-NMR method\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eAverage EN*\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eAverage Molecular Weight\u003csup\u003e#\u003c/sup\u003e\u003c/p\u003e\n \u003cp\u003e(g/mol)\u003c/p\u003e\n \u003c/th\u003e\n \u003c/tr\u003e\n \u003c/thead\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eUE\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e113.27\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e2.62\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e2.31\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e2.47\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e466\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eOE\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e107.59\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e1.74\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e1.73\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e1.74\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e520\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eEE\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e72.57\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e2.30\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e2.00\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e2.15\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e722\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eRE\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e88.69\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e2.12\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e2.00\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e2.06\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e616\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eHE\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e86.58\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e2.15\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e2.20\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e2.18\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e658\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n \u003ctfoot\u003e\n \u003ctr\u003e\n \u003ctd colspan=\"6\"\u003e* EN \u0026ndash; Estolide Number \u003csup\u003e#\u003c/sup\u003e Average molecular weight calculated based on the Average EN\u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tfoot\u003e\n \u003c/table\u003e\n \u003c/div\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec13\" class=\"Section2\"\u003e\n \u003ch2\u003e3.2. Synthesis of estolide monoethanolamides\u003c/h2\u003e\n \u003cp\u003eSynthesis of ethanolamide derivatives of fatty acids has been extensively studied [\u003cspan class=\"CitationRef\"\u003e49\u003c/span\u003e\u0026ndash;\u003cspan class=\"CitationRef\"\u003e53\u003c/span\u003e]. But ethanolamide derivatives of estolides have not been reported earlier. The ethanolamides were synthesized using the catalytic activity of sodium methoxide at elevated temperatures. The synthesized products were evaluated for the conversion and selectivity towards amide formation with the aid of AV and Amine Value as shown in Table\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003e. The synthesized amides were found to have conversion in the range of 78\u0026ndash;86%. Wherein the estolides derived from UA, OA, and EA had higher conversions in comparison to the hydroxy-based estolides. The underlying reason could be the presence of a free hydroxyl group within the estolide molecule of ricinoleic estolide (RE) and 12-hydroxystearic estolide (HE), in addition to the alcohol group of ethanolamine, competing with the amidation reaction. Thus, the ester content for the hydroxy-based estolide amides was observed to be higher in comparison to the other estolides. Overall, the reaction attained more than 90% conversion in 8 hours with an average amide to ester selectivity of 7.4:1.\u003c/p\u003e\n \u003cdiv class=\"gridtable\"\u003e\n \u003ctable id=\"Tab4\" border=\"1\"\u003e\n \u003ccaption language=\"En\"\u003e\n \u003cdiv class=\"CaptionNumber\"\u003eTable 4\u003c/div\u003e\n \u003cdiv class=\"CaptionContent\"\u003e\n \u003cp\u003eAnalysis of Estolide Amides\u003c/p\u003e\n \u003c/div\u003e\n \u003c/caption\u003e\n \u003cthead\u003e\n \u003ctr\u003e\n \u003cth align=\"left\" rowspan=\"2\"\u003e\n \u003cp\u003eSample\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\" rowspan=\"2\"\u003e\n \u003cp\u003eAmine Value\u003c/p\u003e\n \u003cp\u003e(mg KOH/g)\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\" rowspan=\"2\"\u003e\n \u003cp\u003eAcid Value\u003c/p\u003e\n \u003cp\u003e(mg KOH/g)\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\" colspan=\"3\"\u003e\n \u003cp\u003eConversion (%)\u003c/p\u003e\n \u003c/th\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eAmide\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eEster\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eTotal\u003c/p\u003e\n \u003c/th\u003e\n \u003c/tr\u003e\n \u003c/thead\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eUEA\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e16.30\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e9.89\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e83.48\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e6.58\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e90.06\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eOEA\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e13.29\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e5.48\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e85.89\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e8.34\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e94.23\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eEEA\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e13.48\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e5.01\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e79.49\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e12.91\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e92.41\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eREA\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e17.29\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e1.80\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e78.14\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e19.60\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e97.74\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eHEA\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e16.80\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e1.25\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e78.28\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e20.11\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e98.39\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n \u003c/table\u003e\n \u003c/div\u003e\n \u003cp\u003eThe FTIR spectra for estolide ethanolamides, as shown in Fig. \u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003e (c), illustrate the distinct absorbance peaks at 1640\u0026ndash;1646 cm\u003csup\u003e-1\u003c/sup\u003e (C\u0026thinsp;=\u0026thinsp;O stretching for carboxyl, amide), 1545\u0026ndash;1550 cm\u003csup\u003e-1\u003c/sup\u003e (N-O stretching, amide), and 3290\u0026ndash;3305 cm\u003csup\u003e-1\u003c/sup\u003e (N-H stretching, amide), confirming the formation of amide bonds. Further, the presence of strong absorbance peaks at 1730\u0026ndash;1740 cm\u003csup\u003e-1\u003c/sup\u003e (C\u0026thinsp;=\u0026thinsp;O stretching for carboxyl, ester) and 1050\u0026ndash;1070 cm\u003csup\u003e-1\u003c/sup\u003e (C-O stretching, ester) confirmed that the estolide linkages were retained. Similar to the \u003csup\u003e1\u003c/sup\u003eH-NMR spectra of estolides, the estolide amide spectra (Table\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e4\u003c/span\u003e) showed chemical shifts at 2.19\u0026ndash;2.20 and 4.83\u0026ndash;4.87 ppm corresponding to \u0026alpha;-methylene ester and ester methine protons, respectively. For all the synthesized molecules, a distinct chemical shift at 2.26\u0026ndash;2.28 ppm combined with low AV, confirmed the formation amide bond. Interestingly, another peak at 2.51 ppm was observed for undecylenic estolide amide (UEA). This peculiar peak observed could be correlated with the bond migration during the formation of estolides, combined with the lower chain length of UA, leading to a methylene group closer to an estolide linkage as well as an amide bond. This substantiates the highly branched structure of UE and UEA in comparison to the other molecules under study. Further, a peak at 3.7\u0026ndash;3.73 ppm associated with the protons linked to carbon adjacent to the hydroxyl group was observed for all the estolide amides, implying a free alcohol group in the ethanolamine moiety, validating the selectivity of the reaction towards formation of amides.\u003c/p\u003e\n \u003cdiv class=\"gridtable\"\u003e\n \u003ctable id=\"Tab5\" border=\"1\"\u003e\n \u003ccaption language=\"En\"\u003e\n \u003cdiv class=\"CaptionNumber\"\u003eTable 5\u003c/div\u003e\n \u003cdiv class=\"CaptionContent\"\u003e\n \u003cp\u003e\u003csup\u003e1\u003c/sup\u003eH-NMR spectra for estolide amides\u003c/p\u003e\n \u003c/div\u003e\n \u003c/caption\u003e\n \u003cthead\u003e\n \u003ctr\u003e\n \u003cth align=\"left\" rowspan=\"2\"\u003e\n \u003cp\u003eComponent\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\" rowspan=\"2\"\u003e\n \u003cp\u003eChemical Shift\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\" colspan=\"5\"\u003e\n \u003cp\u003eIntegral\u003c/p\u003e\n \u003c/th\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eUEA\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eOEA\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eEEA\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eREA\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eHEA\u003c/p\u003e\n \u003c/th\u003e\n \u003c/tr\u003e\n \u003c/thead\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e-CH\u003csub\u003e3\u003c/sub\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.87\u0026ndash;0.89\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e6.00\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e6.00\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e6.00\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e6.00\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e6.00\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e-CH\u003csub\u003e2\u003c/sub\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e1.18\u0026ndash;2.03\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e57.11\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e53.30\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e78.60\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e44.58\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e63.44\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u0026ndash;CH\u003csub\u003e2\u003c/sub\u003e\u0026ndash;(C\u0026thinsp;=\u0026thinsp;O)\u0026ndash;O\u0026ndash;CH\u003csub\u003e2\u003c/sub\u003e\u0026ndash;\u003c/p\u003e\n \u003cp\u003e(\u0026alpha;-methylene ester)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e2.19\u0026ndash;2.20\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e4.13\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e2.95\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e2.38\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e3.25\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e2.22\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u0026ndash;CH\u003csub\u003e2\u003c/sub\u003e\u0026ndash;(C\u0026thinsp;=\u0026thinsp;O)\u0026ndash;OH\u003c/p\u003e\n \u003cp\u003e(\u0026alpha;-methylene amide)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e2.26\u0026ndash;2.28\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e4.68\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e1.84\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e1.97\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e3.49\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e2.09\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u0026ndash;CH\u003csub\u003e2\u003c/sub\u003e\u0026ndash;(C\u0026thinsp;=\u0026thinsp;O)\u0026ndash;O\u0026ndash;CH\u003csub\u003e2\u003c/sub\u003e\u0026ndash;\u003c/p\u003e\n \u003cp\u003e(\u0026alpha;-methylene amide)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e2.51\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e7.54\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e-NH-CH\u003csub\u003e2\u003c/sub\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e3.41\u0026ndash;3.42\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e4.28\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e2.12\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e2.11\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e2.10\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e1.89\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u0026ndash;CH\u003csub\u003e2\u003c/sub\u003e\u0026ndash;(HC-OH)\u0026ndash;CH\u003csub\u003e2\u003c/sub\u003e\u0026ndash;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e3.57\u0026ndash;3.62\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.88\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.96\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e-CH-OH\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e3.7\u0026ndash;3.73\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e4.02\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e2.20\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e2.11\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e2.20\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e1.94\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u0026ndash;CH\u003csub\u003e2\u003c/sub\u003e\u0026ndash;(C\u0026thinsp;=\u0026thinsp;O)\u0026ndash;O\u0026ndash;CH\u003csub\u003e2\u003c/sub\u003e\u0026ndash;\u003c/p\u003e\n \u003cp\u003e(ester methine)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e4.83\u0026ndash;4.87\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e1.79\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.62\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.90\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.68\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e1.01\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e-CH\u0026thinsp;=\u0026thinsp;CH- (alkene)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e5.38\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e1.35\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e1.42\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e1.07\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e2.78\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.00\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e-N-H\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e5.94\u0026ndash;6.06\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e1.46\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.75\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.99\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e1.15\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.93\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n \u003c/table\u003e\n \u003c/div\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec14\" class=\"Section2\"\u003e\n \u003ch2\u003e3.3. Pendulum tribometer experiments\u003c/h2\u003e\n \u003cdiv id=\"Sec15\" class=\"Section3\"\u003e\n \u003ch2\u003e3.3.1. System damping experiments\u003c/h2\u003e\n \u003cp\u003eThe system damping experiments were conducted to assess the energy loss due to friction at bearings, air resistance, and material damping. A gradual non-linear decay in the oscillation, as shown in Fig. \u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003e (a), was observed with a damping time of approximately 6300 seconds. To take into consideration the viscous drag experienced by the sample disc, the system damping experiments were repeated with the sample plate submerged in the lubricant (similar to the configuration during sliding experiments) at temperatures of 40, 70, and 100˚C. But in comparison to the frictional loss at bearing contact and the air drag, the energy loss due to the viscous drag was found to be negligible, as seen in Fig. \u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003e (b, c, d). Owing to the long damping time of the pendulum, the energy loss per cycle due to the pendulum is very low. But to determine the precise energy dissipation at the tribo-contact during the sliding experiments, the energy dissipation of the pendulum at the no-load condition was subtracted from the total energy dissipation during the sliding experiment (per cycle).\u003c/p\u003e\n \u003c/div\u003e\n \u003cdiv id=\"Sec16\" class=\"Section3\"\u003e\n \u003ch2\u003e3.3.2. Sliding experiments\u003c/h2\u003e\n \u003cp\u003eThe disc samples and the lubricants were prepared as mentioned in section 2.6.1. All the fatty acids and the synthesised molecules were blended in the base oil. Hereafter, the acronym for each additive will be used to refer to its corresponding blend. The sliding experiments were carried out as per the methodology described in section 2.6.2. After the run-in, data from the optical encoder for angular displacement were recorded over a period of time. Figure\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e4\u003c/span\u003e illustrates the damping curves for certain lubricant blends. It can be observed that for the base oil and EE at 100˚C, the damping time is slightly higher than 100 and 150 seconds, respectively, while for the UEA, it lies between 100 to 150 seconds. In comparison to the 6300 seconds of system damping experiments, the sliding experiments exhibited low damping times. This means that the energy dissipation at the tribo-contact is significantly higher than the other energy losses.\u003c/p\u003e\n \u003cdiv class=\"gridtable\"\u003e\n \u003ctable id=\"Tab6\" border=\"1\"\u003e\n \u003ccaption language=\"En\"\u003e\n \u003cdiv class=\"CaptionNumber\"\u003eTable 6\u003c/div\u003e\n \u003cdiv class=\"CaptionContent\"\u003e\n \u003cp\u003eDamping Performance of Lubricants\u003c/p\u003e\n \u003c/div\u003e\n \u003c/caption\u003e\n \u003cthead\u003e\n \u003ctr\u003e\n \u003cth align=\"left\" rowspan=\"2\"\u003e\n \u003cp\u003eSample\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\" colspan=\"3\"\u003e\n \u003cp\u003eNumber of cycles (15˚ \u0026minus;\u0026thinsp;0.5˚)\u003c/p\u003e\n \u003c/th\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003e40˚C\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003e70˚C\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003e100˚C\u003c/p\u003e\n \u003c/th\u003e\n \u003c/tr\u003e\n \u003c/thead\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eBase Oil\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e69.33\u0026thinsp;\u0026plusmn;\u0026thinsp;0.58\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e66.67\u0026thinsp;\u0026plusmn;\u0026thinsp;1.15\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e58.00\u0026thinsp;\u0026plusmn;\u0026thinsp;2.00\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eUA\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e83.00\u0026thinsp;\u0026plusmn;\u0026thinsp;2.65\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e70.00\u0026thinsp;\u0026plusmn;\u0026thinsp;2.65\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e64.67\u0026thinsp;\u0026plusmn;\u0026thinsp;2.52\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eUE\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e74.00\u0026thinsp;\u0026plusmn;\u0026thinsp;0.00\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e73.33\u0026thinsp;\u0026plusmn;\u0026thinsp;0.58\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e72.00\u0026thinsp;\u0026plusmn;\u0026thinsp;2.00\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eUEA\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e77.67\u0026thinsp;\u0026plusmn;\u0026thinsp;1.15\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e67.33\u0026thinsp;\u0026plusmn;\u0026thinsp;0.58\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e66.33\u0026thinsp;\u0026plusmn;\u0026thinsp;0.58\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eOA\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e79.00\u0026thinsp;\u0026plusmn;\u0026thinsp;1.00\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e75.33\u0026thinsp;\u0026plusmn;\u0026thinsp;1.15\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e69.00\u0026thinsp;\u0026plusmn;\u0026thinsp;0.00\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eOE\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e87.00\u0026thinsp;\u0026plusmn;\u0026thinsp;1.00\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e78.33\u0026thinsp;\u0026plusmn;\u0026thinsp;1.53\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e80.33\u0026thinsp;\u0026plusmn;\u0026thinsp;1.15\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eOEA\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e83.00\u0026thinsp;\u0026plusmn;\u0026thinsp;1.00\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e79.67\u0026thinsp;\u0026plusmn;\u0026thinsp;2.31\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e68.33\u0026thinsp;\u0026plusmn;\u0026thinsp;1.53\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eEA\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e90.33\u0026thinsp;\u0026plusmn;\u0026thinsp;1.15\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e91.67\u0026thinsp;\u0026plusmn;\u0026thinsp;2.08\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e87.33\u0026thinsp;\u0026plusmn;\u0026thinsp;1.53\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eEE\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e90.67\u0026thinsp;\u0026plusmn;\u0026thinsp;2.89\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e88.67\u0026thinsp;\u0026plusmn;\u0026thinsp;1.15\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e91.33\u0026thinsp;\u0026plusmn;\u0026thinsp;2.08\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eEEA\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e84.67\u0026thinsp;\u0026plusmn;\u0026thinsp;3.06\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e87.00\u0026thinsp;\u0026plusmn;\u0026thinsp;2.65\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e79.67\u0026thinsp;\u0026plusmn;\u0026thinsp;0.58\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eRA\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e77.67\u0026thinsp;\u0026plusmn;\u0026thinsp;0.58\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e77.67\u0026thinsp;\u0026plusmn;\u0026thinsp;2.52\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e74.00\u0026thinsp;\u0026plusmn;\u0026thinsp;1.00\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eRE\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e74.67\u0026thinsp;\u0026plusmn;\u0026thinsp;1.53\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e71.33\u0026thinsp;\u0026plusmn;\u0026thinsp;0.58\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e74.00\u0026thinsp;\u0026plusmn;\u0026thinsp;2.65\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eREA\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e68.00\u0026thinsp;\u0026plusmn;\u0026thinsp;2.65\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e72.33\u0026thinsp;\u0026plusmn;\u0026thinsp;0.58\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e69.00\u0026thinsp;\u0026plusmn;\u0026thinsp;1.00\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eHE\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e87.00\u0026thinsp;\u0026plusmn;\u0026thinsp;1.00\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e88.00\u0026thinsp;\u0026plusmn;\u0026thinsp;1.73\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e89.33\u0026thinsp;\u0026plusmn;\u0026thinsp;0.58\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eHEA\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e83.00\u0026thinsp;\u0026plusmn;\u0026thinsp;2.00\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e76.00\u0026thinsp;\u0026plusmn;\u0026thinsp;1.00\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e85.67\u0026thinsp;\u0026plusmn;\u0026thinsp;1.15\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\" colspan=\"2\"\u003e\n \u003cp\u003eOverall % relative standard deviation\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" colspan=\"2\"\u003e\n \u003cp\u003e1.86\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n \u003c/table\u003e\n \u003c/div\u003e\n \u003cp\u003eThe relative performance of the lubricants can be determined from the oscillation decay of a pendulum, specifically by counting the number of cycles until the motion ceases. Higher decay time implied lower energy dissipation per cycle, which meant lower COF. The number of cycles for the pendulum to decay from 15\u003cstrong\u003e˚\u003c/strong\u003e to 0.5˚ for all the evaluated lubricants has been reported in Table\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e6\u003c/span\u003e. It was observed that all the synthesised additives (except for REA at 40˚C) showed a higher number of cycles than the base oil, suggesting their ability as OFMs. The % relative standard deviation was as low as 1.86, validating the exceptional repeatability of the experiments. EE at 40˚C, EA at 70˚C, and EE at 100˚C were found to have the highest number of cycles, indicating lower COF. But the number of cycles cannot be used to compare quantitative values of COF. The underlying reason is the change in COF with sliding velocity, as established by the Stribeck equation [\u003cspan class=\"CitationRef\"\u003e54\u003c/span\u003e]. The average sliding velocity decreases with successive cycles, leading to a change in COF, whose magnitude could vary for different lubricants. This variation can be seen in Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e4\u003c/span\u003e, wherein the rate of decay increased rapidly for base oil in comparison to the EE at lower amplitudes of oscillation, suggesting a rise in COF. Thus, it is crucial to determine the Stribeck Curves of the evaluated lubricants at such lower sliding velocities.\u003c/p\u003e\n \u003c/div\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec17\" class=\"Section2\"\u003e\n \u003ch2\u003e3.4. Evaluation of the coefficient of friction\u003c/h2\u003e\n \u003cp\u003eThe coefficient of friction was calculated using the damping curves of the sliding and the system damping experiments as reported by Divakaran et al. [\u003cspan class=\"CitationRef\"\u003e46\u003c/span\u003e]. Figures \u003cspan class=\"InternalRef\"\u003e5\u003c/span\u003e, \u003cspan class=\"InternalRef\"\u003e6\u003c/span\u003e, and \u003cspan class=\"InternalRef\"\u003e7\u003c/span\u003e illustrate the COF for fatty acids, estolides, and estolide amides, respectively. Among the curves, many have a spike in COF at lower velocities (less than 2 mm/sec). This occurrence of a sudden increase in COF can probably be a result of the transition from sliding to stick-slip at lower velocities [\u003cspan class=\"CitationRef\"\u003e55\u003c/span\u003e]. Also, it was observed that at low temperature, the COF curves were smooth, while at elevated temperature, noisy curves were obtained, especially for fatty acids and estolide amides. Various molecular properties of the OFMs, like the functional groups, molecular structure, packing efficiency, adsorption, and desorption, could lead to this variation [\u003cspan class=\"CitationRef\"\u003e14\u003c/span\u003e, \u003cspan class=\"CitationRef\"\u003e56\u003c/span\u003e] and thus need to be discussed in detail.\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec18\" class=\"Section2\"\u003e\n \u003ch2\u003e3.5. Molecular Structure of OFMs and Friction in the BL\u003c/h2\u003e\n \u003cdiv class=\"gridtable\"\u003e\n \u003cp\u003eTable 7 depicts the physicochemical properties of the molecules in terms of their theoretical MW and experimental PP, and frictional values of their blends (averaged over the sliding velocity of 2 to 13 mm/sec; to eliminate the fluctuation due to stick-slip transition). Distinct, temperature-dependent performance was observed across the additive classes. At the lower and higher temperatures of 40\u0026deg;C and 100\u0026deg;C, the estolides exhibited superior frictional performance, achieving average reductions of 13.92% and 29.92%, respectively, relative to the base oil. In contrast, at the intermediate temperature of 70\u0026deg;C, the fatty acids were most effective, yielding an average friction reduction of 16.63%. While the estolide amides were less effective, a substantial lowering of friction was still recorded compared to the base oil. Notably, exceptional performance was demonstrated by EE, which emerged as the best OFM with a remarkable 36.91% reduction in COF at 100\u0026deg;C. Despite these additive class-specific trends, it is clear from Table 7 that significant performance variations exist within each group, emphasising the critical role of molecular structures in determining tribological efficacy.\u003c/p\u003e\n \u003cp\u003eThe fatty acids under study have subtle differences in molecular structure, wherein UA has terminal unsaturation. OA and EA have unsaturation within the chain, while RA has a hydroxyl group in addition to the unsaturation. Although not studied in this acid form, owing to its insolubility in the base oil, the hydroxystearic acid has a hydroxyl group with no unsaturation. The transformation of fatty acid to estolide is accompanied by an increase in molecular weight and a decrease in pour point (PP) [17\u0026ndash;20]. This reduction in the PP is attributed to the introduction of branching, resulting in reduced packing efficiency [57, 58]. Further transformation from estolide to ethanolamide leads to a significant increase in the packing efficiency as reported in the literature [14, 59]. But the amides have a different polar head group than the fatty acids and estolides, having an amide bond and a free alcohol moiety.\u003c/p\u003e\n \u003c/div\u003e\n \u003cp\u003eTable \u003cspan class=\"InternalRef\"\u003e7\u003c/span\u003e: Physicochemical properties of synthesized OFMs and Frictional properties of their blends\u003c/p\u003e\n \u003cp\u003e\u003cimg 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\"\u003e\u003c/p\u003e\n \u003cdiv id=\"Sec19\" class=\"Section3\"\u003e\n \u003ch2\u003e3.5.1. Frictional Performance at 40˚C\u003c/h2\u003e\n \u003cp\u003eAt 40˚C, the fatty acids, having higher packing efficiency (higher PP) were seen to have lower COF. Higher packing efficiency of the OFMs has been reported to form a stable adsorbed film providing enhanced protection, especially in the BL regime [\u003cspan class=\"CitationRef\"\u003e5\u003c/span\u003e, \u003cspan class=\"CitationRef\"\u003e60\u003c/span\u003e, \u003cspan class=\"CitationRef\"\u003e61\u003c/span\u003e]. Similarly, the estolides and amides with comparatively higher packing were found to have lower friction. The friction reduction ability of UE in comparison to UA was drastically reduced, owing to the significant drop in the packing efficiency as a result of the highly branched molecular structure of UE [\u003cspan class=\"CitationRef\"\u003e19\u003c/span\u003e]. Similarly, derivatives of RA exhibited poor frictional performance due to inadequate packing. Except for the poorly packed molecule (UE, UEA, RE \u0026amp; REA), the variation in friction, as a result of different molecular structures, was reduced in estolides and amides due to higher MW and van der Waals forces. Higher MW and van der Waals forces have been extensively reported to aid the formation of a robust and stronger adsorbed film on the metal surface, decreasing COF in BL regime [\u003cspan class=\"CitationRef\"\u003e62\u003c/span\u003e\u0026ndash;\u003cspan class=\"CitationRef\"\u003e65\u003c/span\u003e].\u003c/p\u003e\n \u003c/div\u003e\n \u003cdiv id=\"Sec20\" class=\"Section3\"\u003e\n \u003ch2\u003e3.5.2. Frictional Performance at 70˚C\u003c/h2\u003e\n \u003cp\u003eContrary to the trend observed at 40˚C, the magnitude of friction reduction at 70˚C showed a strong correlation with molecular weight, a relationship that was particularly pronounced for fatty acids. At elevated temperatures, the limiting factor for the stability of the adsorbed film is the rate of desorption, which is higher for molecules with lower MWs [\u003cspan class=\"CitationRef\"\u003e59\u003c/span\u003e]. For fatty acids, estolides as well as amides, the friction was observed to decrease with the MW as we compare the undecylenic, oleic, and erucic derivatives counterparts, establishing a critical role of MW. Except for RE and HEA, the larger molecules within the group, like EA, RA, EE, HE, EEA, REA, showed enhanced frictional response during sliding at 70˚C than at 40˚C, confirming the critical role of MW at elevated temperature. In addition, poor packing of the adsorbed film, correlated by lower PP, was seen to decrease the additive efficacy as observed for undecylenic and ricinoleic derivatives. An additional factor contributing to the improved frictional performance is the chemisorption of the adsorbed molecules to form metal oxide soaps [\u003cspan class=\"CitationRef\"\u003e5\u003c/span\u003e, \u003cspan class=\"CitationRef\"\u003e46\u003c/span\u003e, \u003cspan class=\"CitationRef\"\u003e66\u003c/span\u003e]. The extent of this improvement is governed by both the probability of chemisorption and the requisite activation energy [\u003cspan class=\"CitationRef\"\u003e66\u003c/span\u003e]. The probability, in turn, depends on the stability of the initial physisorbed film, which is inversely related to the rate of desorption [\u003cspan class=\"CitationRef\"\u003e59\u003c/span\u003e, \u003cspan class=\"CitationRef\"\u003e63\u003c/span\u003e]. The activation energy is a function of molecular complexity and molecular weight [\u003cspan class=\"CitationRef\"\u003e67\u003c/span\u003e]. The reduction in the COF with increasing temperature (from 40\u0026deg;C to 70\u0026deg;C) was more significant for EA than for EE. This difference can be attributed to the higher activation energy expected for the estolide; owing to its sterically hindered carboxylic group and greater molecular weight, it requires more thermal energy to effectively transition from physisorption to chemisorption. For other molecules studied, this effect was less pronounced due to a complex interplay of factors, including molecular weight and packing efficiency, in addition to chemisorption [\u003cspan class=\"CitationRef\"\u003e56\u003c/span\u003e, \u003cspan class=\"CitationRef\"\u003e68\u003c/span\u003e].\u003c/p\u003e\n \u003c/div\u003e\n \u003cdiv id=\"Sec21\" class=\"Section3\"\u003e\n \u003ch2\u003e3.5.3. Frictional Performance at 100˚C\u003c/h2\u003e\n \u003cp\u003eThe trend in the frictional values for sliding experiments at 100˚C varied from that at 40˚C and 70˚C. For all the fatty acids, the COF was higher and correlated inversely with the MW of the molecules. Although at 100˚C, the molecules had substantial energy to undergo chemisorption, the higher desorption rates limited the probability of chemisorption [\u003cspan class=\"CitationRef\"\u003e59\u003c/span\u003e], leading to poor fractional performance. On the other hand, the estolides, owing to their higher MW and thus lower desorption rates, had a higher probability of chemisorption, leading to a lower COF at 100˚C. Unlike fatty acids, the effect of packing efficiency was significant for estolides even at the elevated temperature, as the COF of RE was observed to be higher than OE, despite the higher MW of the former. In the case of amides (except for HEA), despite their higher MW, the friction was higher at 100˚C due to the inability of the -OH head group to undergo chemisorption. Interestingly, the performance of large molecules of amides was observed to be inferior to their significantly smaller fatty acid counterparts, signifying the importance of the ability to chemisorb at elevated temperatures.\u003c/p\u003e\n \u003c/div\u003e\n\u003c/div\u003e"},{"header":"4. Conclusion","content":"\u003cp\u003e\u003col\u003e\u003cspan\u003e\u003cli\u003e\u003cp\u003eEstolide and Estolide ethanolamide derivatives of fatty acids, including undecylenic, oleic, erucic, ricinoleic, and hydroxystearic acids, were synthesised and characterised using FTIR and \u003csup\u003e1\u003c/sup\u003eH-NMR.\u003c/p\u003e\u003c/li\u003e\u003c/span\u003e\u003cspan\u003e\u003cli\u003e\u003cp\u003eThe fatty acids and the synthesised OFMs were evaluated for their ability to reduce friction in the boundary lubrication regime using a custom-built FCPeT. The experiments were found to be repeatable with friction reductions in the range of 10\u0026ndash;30%.\u003c/p\u003e\u003c/li\u003e\u003c/span\u003e\u003cspan\u003e\u003cli\u003e\u003cp\u003eThis study established the role of molecular structure, characterised by the functional group, branching, and molecular weight, in the variation of the COF at different temperatures.\u003c/p\u003e\u003c/li\u003e\u003c/span\u003e\u003cspan\u003e\u003cli\u003e\u003cp\u003eTransformation to estolides improves the frictional performance, especially at elevated temperatures of 100˚C. Estolide ethanolamide, owing to its inability to chemisorb, illustrated inferior performance to the fatty acids and estolides.\u003c/p\u003e\u003c/li\u003e\u003c/span\u003e\u003cspan\u003e\u003cli\u003e\u003cp\u003eEA, EE, and EEA consistently demonstrated the lowest performance within their respective classes across the entire temperature range studied, emphasizing the impact of higher molecular weight and relatively lower branching in achieving optimal OFM performance.\u003c/p\u003e\u003c/li\u003e\u003c/span\u003e\u003c/ol\u003e\u003c/p\u003e"},{"header":"Statements \u0026 Declarations ","content":"\u003cp\u003e\u003cstrong\u003eFunding\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThis work was supported by the Department of Science and Technology, India, through its INSPIRE Fellowship program.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eCompeting Interests\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors have no relevant financial or non-financial interests to disclose.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAuthor Contributions\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eAll authors contributed to the study conception and design. Material preparation was performed by Prasad Sanap, Somesh Patil, Bhagesh Kori, Nidhi Jain, Rakshit Sinha and Viraj Tungare. Data collection and analysis were performed by Prasad Sanap and Vikas Kumar Singh. The first draft of the manuscript was written by Prasad Sanap and Vikas Kumar Singh. Amit Pratap and Satish V Kailas read and approved the final manuscript\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n\u003cli\u003eSpikes, H.: Friction Modifier Additives. Tribol. Lett. 2015 601. 60, 1\u0026ndash;26 (2015). https://doi.org/10.1007/S11249-015-0589-Z\u003c/li\u003e\n\u003cli\u003eRomsdahl, T., Shirani, A., Minto, R.E., Zhang, C., Cahoon, E.B., Chapman, K.D., Berman, D.: Nature-Guided Synthesis of Advanced Bio-Lubricants. Sci. Rep. 9, (2019). https://doi.org/10.1038/s41598-019-48165-6\u003c/li\u003e\n\u003cli\u003eFry, B.M., Moody, G., Spikes, H.A., Wong, J.S.S.: Adsorption of Organic Friction Modifier Additives. 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Compd. 40, 222\u0026ndash;226 (2004). https://doi.org/10.1023/B:CONC.0000039128.78645.A8\u003c/li\u003e\n\u003cli\u003eBrenna, E., De Fabritiis, V., Parmeggiani, F., Tentori, F., Tessaro, D.: Lipase-Mediated Synthesis of Oleoyl Ethanolamide Starting from High-Oleic Sunflower Oil Soapstock. ACS Sustain. Chem. Eng. 11, 2764\u0026ndash;2772 (2023). https://doi.org/10.1021/ACSSUSCHEMENG.2C05598/ASSET/IMAGES/LARGE/SC2C05598_0006.JPEG\u003c/li\u003e\n\u003cli\u003eWang, X., Chen, Y., Jin, Q., Huang, J., Wang, X.: Synthesis of Linoleoyl Ethanolamide. J. Oleo Sci. 62, 427\u0026ndash;433 (2013)\u003c/li\u003e\n\u003cli\u003eLu, X., Khonsari, M.M., Gelinck, E.R.M.: The Stribeck Curve: Experimental Results and Theoretical Prediction. J. Tribol. 128, 789\u0026ndash;794 (2006). https://doi.org/10.1115/1.2345406\u003c/li\u003e\n\u003cli\u003eStoica, N.A., Tudor, A.: Some aspects concerning the behaviour of friction materials at low and very low sliding speeds. Tribol. Ind. 37, 374\u0026ndash;379 (2015)\u003c/li\u003e\n\u003cli\u003eJahanmir, S., Beltzer, M.: Effect of Additive Molecular Structure on Friction Coefficient and Adsorption. J. Tribol. 108, 109\u0026ndash;116 (1986). https://doi.org/10.1115/1.3261129\u003c/li\u003e\n\u003cli\u003eRodrigues, J.D.A., Cardoso, F.D.P., Lachter, E.R., Estev\u0026atilde;o, L.R.M., Lima, E., Nascimento, R.S.V.: Correlating chemical structure and physical properties of vegetable oil esters. JAOCS, J. Am. Oil Chem. Soc. 83, 353\u0026ndash;357 (2006). https://doi.org/10.1007/S11746-006-1212-0;PAGE:STRING:ARTICLE/CHAPTER\u003c/li\u003e\n\u003cli\u003eMenger, F.M., Wood, M.G., Richardson, S., Zhou, Q., Elrington, A.R., Sherrod, M.J.: Chain-Substituted Lipids in Monolayer Films. A Study of Molecular Packing. J. Am. Chem. Soc. 110, 6797\u0026ndash;6803 (1988). https://doi.org/10.1021/JA00228A032/ASSET/JA00228A032.FP.PNG_V03\u003c/li\u003e\n\u003cli\u003eBigelow, W.C., Glass, E., Zisman, W.A.: Oleophobic monolayers. 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Interfaces. 16, 14252\u0026ndash;14262 (2024). https://doi.org/10.1021/ACSAMI.3C16432/SUPPL_FILE/AM3C16432_SI_001.PDF\u003c/li\u003e\n\u003cli\u003eNalam, P.C., Pham, A., Castillo, R.V., Espinosa-Marzal, R.M.: Adsorption Behavior and Nanotribology of Amine-Based Friction Modifiers on Steel Surfaces. J. Phys. Chem. C. 123, 13672\u0026ndash;13680 (2019). https://doi.org/10.1021/ACS.JPCC.9B02097/SUPPL_FILE/JP9B02097_SI_001.PDF\u003c/li\u003e\n\u003cli\u003eLevine, O., Zisman, W.A.: Physical properties of monolayers adsorbed at the solid-air interface. I. Friction and wettability of aliphatic polar compounds and effect of halogenation. J. Phys. Chem. 61, 1068\u0026ndash;1077 (1957). https://doi.org/10.1021/J150554A008/ASSET/J150554A008.FP.PNG_V03\u003c/li\u003e\n\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":true,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true},"keywords":"Estolides, Estolide ethanolamides, Organic friction modifiers, Boundary lubrication, Force-Controlled Pendulum Tribometer","lastPublishedDoi":"10.21203/rs.3.rs-7921826/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-7921826/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eThis study evaluates the performance of various fatty acids like undecylenic, oleic, erucic, ricinoleic and 12-hydroxystearic acid, their estolides and estolide ethanolamides in the boundary lubrication regime. The influence of molecular structure variation in terms of functional groups, branching and molecular weight on the frictional behavior of these Organic Friction Modifiers (OFMs) at elevated temperatures (40˚C, 70˚C, and 100˚C) has been studied. A custom-built Force-Controlled Pendulum Tribometer (FCPeT) was used to evaluate the friction of the OFMs at a concentration of 0.1% w/w in group III (32 cSt) base oil. The results demonstrated repeatable frictional response which varied significantly with temperature. At 40˚C, the stability of adsorbed film was found to be eminent, leading to lower friction for molecules with higher packing efficiency. At 70˚C, the molecular weight was found to be critical, owing to its inverse relation with desorption rate, leading to stronger adsorbed films. For a higher temperature of 100˚C, the ability to chemisorb was found to be important to achieve lower friction. Erucic acid and its estolide and estolide ethanolamide derivatives were found to perform efficiently across the range of temperatures studied. The study concludes that the molecular structure significantly influences the efficiency of the OFMs, with the ability to chemisorb onto the metal surface, higher molecular weight and low branching being the desired features for optimal performance of OFMs.\u003c/p\u003e","manuscriptTitle":"Boundary lubrication performance of fatty acid and its derivatives using energy dissipation method","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-11-13 10:50:58","doi":"10.21203/rs.3.rs-7921826/v1","editorialEvents":[{"type":"communityComments","content":0}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"7e29907b-0fa6-4ecb-8617-1bd9804f7a9f","owner":[],"postedDate":"November 13th, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[],"tags":[],"updatedAt":"2025-12-04T12:23:51+00:00","versionOfRecord":[],"versionCreatedAt":"2025-11-13 10:50:58","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-7921826","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-7921826","identity":"rs-7921826","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}