## 3 Results and Discussion
### UV-Vis Analysis of Nanoparticle Dispersion  
The stability of the formulated nanolubricants was assessed using a UV-Vis spectrophotometer. This method enabled the determination of peak absorbance and identification of the optimal wavelength from the obtained scan results. The absorbance values  
Figure 6: FTIR spectra: SiO\({}_{2}\) nanoparticles coated with KH570-silane coupling agent. Figure 7: FTIR spectra: (**a**) reference lubricant (Mistral 15W40) and corresponding nanolubricants, and (**b**) reference biolubricant (PLANTO MOT SAE 10W40) and corresponding nanobiolubricants. for SiO\({}_{2}\)/Mistral 15W40 and SiO\({}_{2}\)/PLANTO MOT SAE 10W40 nanolubricants at weight concentrations of 0.25%, 0.50%, 0.75%, and 1.00% are presented in Figure 8, covering wavelengths from 190 nm to 900 nm, which indicates that the peak absorbance for all the tested nanolubricants consistently occurred at a wavelength of 296 nm. The absorbance values recorded at a wavelength of approximately 300 nm characterize the presence of SiO\({}_{2}\) nanoparticles [21; 26]. Figure 9 presents the peak absorbance values of SiO\({}_{2}\)/Mistral 15W40 nanolubricants at various concentrations and under different preparation conditions (stirring and sonication times) over a 77-day period. The peak absorbance values were measured immediately after preparation (0 days) and at subsequent time points: 1 day, 3 days, 7 days, 15 days, 30 days, 54 days, and 77 days. For the 0.25% SiO\({}_{2}\) sample, the peak absorbance values at 0 days for different sonication times (0 h, 1 h, 2.5 h) are relatively close: 3.478, 3.508, and 3.366, respectively (these values are dimensionless because they are calculated as the logarithm of the ratio of incident light to transmitted light through a sample). Over time, all samples show a gradual decrease in absorbance, with the highest sonication time (2.5 h) exhibiting slightly better stability. For the 0.50% SiO\({}_{2}\) sample, the initial peak absorbance values are lower than those of the 0.25% sample, but show a similar pattern: 2.919, 2.642, and 2.561. Again, the sample with 2.5 h sonication demonstrates better stability over time. For the 0.75% SiO\({}_{2}\) sample, the initial peak absorbance values are 2.407, 2.405, and 2.345. Similar to the previous concentrations, higher sonication times tend to maintain higher absorbance values over time. For the 1.0% SiO\({}_{2}\) sample, the initial peak absorbance values are 2.209, 2.051, and 1.991. The trend of better stability with increased sonication time is observed here as well. Across all concentrations, there is a general decrease in peak absorbance values over the 77-day period. The rate of decrease is faster in the initial days (up to 15 days) and tends to stabilize somewhat after 30 days. Samples with higher initial sonication times (2.5 h) show a slower rate of decrease, indicating better dispersion stability. Higher concentrations (0.75% and 1.0%) show lower initial peak absorbance values compared to lower concentrations (0.25% and 0.50%). Despite this, higher concentrations also show significant improvements in stability with increased sonication times. Figure 10 shows the peak absorbance values of SiO\({}_{2}\)/PLANTO MOT SAE 10W40 nanobiolubricants at various concentrations and under different preparation conditions (stirring and sonication times) over a 77-day period. The peak absorbance values were measured immediately after preparation (0 days) and at several subsequent time points: 1 day, 3 days, 7 days, 15 days, 30 days, 54 days, and 77 days. For the 0.25% SiO\({}_{2}\) sample, the initial peak absorbance values are quite close for different sonication times: 3.480, 3.509, and 3.486. Over time, the sample with the highest sonication time (2.5 h) shows a slower rate of decrease, indicating better stability. For the 0.50% SiO\({}_{2}\) sample, the initial peak values are 3.419, 2.967, and 2.678. Samples with 1 h and 2.5 h of sonication show better stability over time, with 2.5-h samples showing the best long-term stability.