Recent Techniques to Enhance Frictional Performance of Polyalphaolefins Using Nanotechnology

Abstract

Polyalphaolefins (PAOs) are synthetic base oils known for their high thermal stability, excellent lubrication, and low volatility [1]. As modern systems demand higher efficiency and reduced wear under extreme operating conditions, researchers have pursued additive-based enhancements to further improve the performance of PAO-based lubricants. This paper investigates three recent advancements in PAO-based lubrication, focusing on tribological behavior and surface interaction mechanisms. The first strategy incorporates copper nanoparticles dispersed in PAO 4 oil on a four-ball tribometer, demonstrating substantial reductions in friction and wear through tribofilm formation and nanoparticle rolling action, leading to over a 51 percent decrease in coefficient of friction [2]. The second approach employs hybrid nanomaterials combining methyl silicone resin with copper nanoparticles in a methyl silicone resin matrix, along with multi-walled carbon nanotubes (MWCNTs) and hexagonal boron nitride (h-BN), which act as rolling elements and surface repair agents, improving load capacity and achieving a 37 percent wear reduction [3]. The third technique utilizes methyl silicone resin additives that generate SiO₂-rich tribofilms in situ under thermal and mechanical stress, significantly improving wear resistance by up to 87 percent without the need for external nanoparticle synthesis at 25°C [4]. These studies confirm that, when combined with triboactive or nano additive systems, PAO lubricants can significantly outperform traditional formulations in minimizing friction and wear. The paper concludes by emphasizing the importance of additive chemistry, dispersion stability, and contact mechanics in next-generation synthetic lubricant design.

1. Introduction

As engineering systems evolve toward higher power densities and longer service intervals, lubricants play an increasingly critical role in mechanical reliability. Frictional losses in sliding and rotating components account for a substantial portion of global energy waste [5], prompting the need for base oils with excellent lubricating properties that increase energy efficiency while minimizing wear. Lubricants that also resist oxidation and maintain viscosity under extreme conditions enable extended drain intervals, reducing waste and maintenance costs.

Polyalphaolefins (PAOs) are a leading class of synthetic base oils, widely favored over conventional mineral oils due to their superior performance characteristics. Unlike mineral oils, which are derived from crude oil refining and contain a broad mixture of hydrocarbons, PAOs are chemically synthesized to have a uniform molecular structure. This uniformity results in a higher viscosity index, meaning PAOs maintain more stable viscosity across wide temperature ranges which is critical for effective lubrication in diverse operating environments. Additionally, PAOs offer excellent oxidative stability, low volatility, and reduced formation of deposits compared to mineral oils, making them ideal for high-performance applications. [6].

Despite these favorable baseline properties, PAO-based lubricants often require further enhancement to meet the increasingly demanding requirements of modern machinery such as high-speed electric drivetrains and aerospace components. These lubrication environments, dominated by direct surface contact and extreme stress – such as high-load aerospace bearings - necessitate the use of functional additive systems. Additives that form protective tribofilms prevent adhesive and abrasive wear, improving component lifespan and maintaining frictional stability.

Recent research has introduced three promising strategies to enhance the frictional behavior of PAOs. The first involves dispersing copper nanoparticles directly in PAO 4 oil, which reduces friction and wear through tribofilm formation and nanoparticle rolling effects [2]. The second strategy employs hybrid nanomaterials combining multi-walled carbon nanotubes (MWCNTs) and hexagonal boron nitride (h-BN) as rolling and surface repair agents, sometimes alongside methyl silicone resin, to improve load capacity and sliding smoothness [3]. The third approach uses methyl silicone resin additives that generate protective SiO₂ tribofilms in situ under thermal and mechanical stress, significantly reducing wear without the need for externally synthesized nanoparticles [4].

2. Literature Review

2.1 Friction Reduction via Copper Nanoparticles in PAO 4 Oil
As mechanical systems face increasing demands for efficiency, reliability, and longevity, friction and wear at contact surfaces remain critical challenges. Traditional lubricants, while effective, often fall short under extreme conditions or prolonged operation. Synthetic base oils like polyalphaolefins offer improved thermal stability and viscosity control over mineral oils, but their tribological performance can be further enhanced through nanotechnology-based additives. Among these, metallic nanoparticles have shown significant promise in reducing surface friction and material degradation during operation. 
Figure 1. Block diagram of four-ball tester. Adapted from [2].

A study conducted by Varalakshmi and Reddy investigated the tribological performance of PAO 4 base oil enhanced with copper (Cu) nanoparticles synthesized via solution-phase chemical reduction [2]. The experimental setup, as seen in Figure 1, followed ASTM D4172-18 using a four-ball tribometer, with tests conducted under standard operating conditions of 392 N load, 1200 rpm rotation speed, and constant temperature of 75 °C for 60 minutes. Copper nanoparticles were dispersed in PAO 4 oil at concentrations ranging from 0.2 to 1.4 weight percent using magnetic stirring and ultrasonic mixing, then evaluated for their impact on the coefficient of friction and wear scar diameter.

The results of the study, displayed in Figure 2, demonstrated substantial benefits. The optimal concentration of 1.0 weight percent Cu nanoparticles led to a 51.85 percent reduction in the coefficient of friction compared to pure PAO 4 oil. This improvement was due to multiple reasons: tribofilm formation on the contact surfaces, nanoparticle rolling action that reduced shear resistance, and a sintering effect that smoothed microscopic roughness. These effects collectively decreased the energy losses associated with friction and minimized abrasive wear between steel surfaces. Beyond this optimal threshold, however, the COF increased again which the authors hypothesized is due to nanoparticle agglomeration and rupture of the lubricating film. 

Surface analysis supported these findings. SEM images of worn surfaces lubricated with Cu-enhanced PAO 4 oil showed smoother textures and smaller wear scars compared to those using base oil alone, as seen in Figure 3. EDX analysis further confirmed the deposition of copper on the contact surfaces, indicating tribochemical interaction between the additive and the steel substrate. The 1.0 weight percent Cu sample exhibited minimal wear and created a stable protective layer that prevented direct metal-to-metal contact.

These findings highlight the viability of copper nanoparticles as effective additives in PAO-based lubricants, particularly for applications where minimizing friction and wear is essential. The key factors for success included nanoparticle stability, uniform dispersion, and controlled concentration levels. As industrial systems evolve toward higher performance thresholds, nano-enhanced lubricants like Cu-PAO 4 blends offer a scalable and energy-efficient solution for friction management. Broader adoption of such formulations could improve machine reliability, extend component life, and reduce energy consumption across transportation, manufacturing, and aerospace sectors.

2.2 Friction Reduction via Methyl Silicone Resin and Copper Nanoparticle Additives
While the direct incorporation of copper nanoparticles into PAO 4 demonstrates significant friction and wear improvements, a 2024 study has explored more advanced additive techniques to address limitations in nanoparticle dispersion and thermal stability. Unlike conventional base oils such as PAO 4, this system utilizes a standalone methyl silicone carrier PAO 20, chosen for its compatibility with nanoscale additives. Guimarey et al. focused on multi-walled carbon nanotubes (MWCNTs) and hexagonal boron nitride (h-BN) as 1D and 2D nanoadditives, respectively [3]. Shown in figure 4, the nano lubricants were prepared by dispersing MWCNTs and h-BN at various concentrations into PAO 20.

Tribological tests using a ball-on-disk configuration at room temperature and a 20 N load revealed that both nanoadditives improved friction reduction and wear resistance. Specifically, h-BN at 0.05 weight percent reduced the wear area by up to 37 percent, while MWCNTs achieved a 29 percent reduction at the same concentration. These hybrid systems offer greater control over additive behavior, particularly in high-temperature regimes where base oil degradation and additive sedimentation pose challenges. The results shown in Figure 5a revealed that the dual-additive formulation significantly reduced the COF and degradation when compared to both neat PAO 4 and single-additive blends. 

At 100°C, the hybrid lubricant reduced the coefficient of friction by 41.2 percent relative to the unmodified base oil, and the wear scar diameter remained consistently smaller across the tested range. However, it is not specified whether this friction reduction persists at temperatures above 125°C, or if lubricant degradation and performance decline resume beyond this threshold. Figure 6 depicts SEM imaging which showed smoother contact surfaces with fewer abrasive features, while thermal degradation of the oil was minimized, indicating stable lubrication even under heat intensive conditions.
Mechanically, MWCNTs act as nanoscale rollers between contacting surfaces due to their tubular structure, which reduces direct contact and shear stress. Their high aspect ratio and flexibility allow them to align and distribute loads effectively, minimizing friction and wear. Meanwhile, hexagonal boron nitride (h-BN), with its layered 2D structure and weak van der Waals forces, allows for easy shear between layers, providing a solid lubricating film that reduces surface adhesion and protects against abrasive wear. Both nanoadditives improve dispersion stability within the base oil, preventing particle agglomeration and ensuring consistent lubrication performance. Together, these effects contribute to a stable low-friction and anti-wear regime under mechanical stress [3].

These findings emphasize the potential of dual-additive nano lubricants in expanding the functional range of PAO 4-based systems. While this study did not utilize PAO 4 as the base fluid, the findings are highly relevant to PAO-class lubricants operating under similar thermal and mechanical loads. For applications such as automotive or aerospace systems where PAO 4 is commonly employed, integrating resin-based dispersants and hybrid nanomaterials could offer comparable friction reduction benefits.

2.3 Synergistic Friction Reduction Using SiO₂
Recent research by Wang et al. (2024) provides a detailed investigation into the frictional and anti-wear behavior of polyalphaolefin (PAO 4) lubricants enhanced with methyl silicone resin additives [4]. This study diverges from Sections 2.1 and 2.2, which rely on externally synthesized nanoparticles, this study highlights a self-generating nanostructure mechanism, where methyl silicone resin reacts under thermal and mechanical stress to form a protective SiO₂ layer.

The authors prepared hybrid formulations by dissolving methyl silicone resin into methyl silicone oil and dispersing it into PAO 4 at concentrations ranging from 0.01 to 0.05 weight percent. Tribological testing was conducted on a four-ball friction tester at a constant load of 98 N and a rotational speed of 1450 rpm across multiple temperatures (25°C to 100°C). Results showed minimal change in the average COF compared to neat PAO 4, but significant improvements in COF stability and wear resistance were observed at 0.02 weight percent. Figure 7 illustrates this effect: while COF reduction was modest, wear scar diameter (WSD) was sharply reduced, indicating improved boundary film formation and surface protection [4].

Figure 8 further proves the significant anti-wear effect of methyl silicone resin additives in PAO 4. The wear volume and wear rate measurements across the tested temperature range confirm that the addition of methyl silicone resin notably reduces material loss during friction. Notably, the wear volume was reduced by over 87 percent at 25 °C and maintained substantial reductions even at 100 °C, demonstrating the additive’s effectiveness in protecting surfaces under varying thermal conditions. This evidence supports the role of methyl silicone resin in forming a robust boundary film that enhances surface durability and frictional stability in PAO 4-based lubricants [4].

Displayed in Figure 9, these SiO₂ particles fill surface grooves, reduce abrasive contact, and form a tribochemical film that adheres to metal surfaces, as confirmed by SEM, EDS, and XPS analyses. However, the long-term stability of this tribofilm under repeated thermal cycling remains to be investigated, which is critical for assessing its durability and industrial viability over extended service periods. Notably, EDS revealed increased surface concentrations of silicon and oxygen, while Raman and XPS spectra confirmed the presence of Si-O and SiO₂ bonding. This tribofilm acts both as a thermal barrier and as a rolling interface that reduces adhesive wear. Wear rate reductions reached 87.3 percent at 25°C and remained significant even at 100°C, where a 50.6 percent improvement was observed.

Unlike conventional nano-additive approaches that require external synthesis of dispersible solid particles, this method generates the functional nanoparticles directly under operating conditions. This self-forming behavior enhances environmental compatibility and additive stability by eliminating the need for separate surfactants or dispersants. These findings reinforce the potential of chemically active resin additives in creating dynamic protective tribofilms within PAO 4 systems, offering a robust frictional solution adaptable to various thermal loads [4].

3. Conclusion

Advancements in nanotechnology-based additives have significantly expanded the functional potential of polyalphaolefins, particularly in demanding thermal and mechanical environments. This paper explored three recent strategies for enhancing the frictional and anti-wear performance of PAO-based lubricants using nanoscale additives and hybrid formulations. The first method utilized multi-walled carbon nanotubes (MWCNTs) and methyl silicone resin to create a dual-functional film that improved interfacial strength and reduced direct surface contact [2]. The second approach incorporated copper nanoparticles and silicone resin into a hybrid dispersion, improving stability and performance across elevated temperatures and high-load regimes [3]. The third technique enabled on site formation of SiO₂ nanoparticles through the thermal decomposition of methyl silicone resin, eliminating the need for external dispersants and contributing to a durable tribochemical film at the sliding interface [4].

Each of these innovations highlights a shift away from inert additives toward functionally active systems that can adapt to and respond within real-time tribological environments. Notably, the emergence of additive systems that self-generate protective nanoparticles under operational stress presents a promising path forward for environmentally friendly, high-performance lubricants [5]. These findings demonstrate that tribofilm formation, dispersion stability, and nanoscale rolling effects are no longer isolated benefits, but can be combined through rational additive design.

Looking ahead, further studies should evaluate the long-term thermal cycling behavior of these formulations, as well as their oxidative stability under real-world service conditions. Additionally, comparative testing with actual PAO 4-based commercial oils across multiple substrate materials (steel–aluminum) may better predict industrial applicability. Future studies should also examine oxidation stability and additive depletion rates under long-term use to complement the mechanical performance focus, ensuring comprehensive evaluation of lubricant durability. As mechanical systems grow more compact and energy-dense, lubricant technologies must evolve accordingly, and these nanostructured additive systems offer a promising route to meet that challenge.

About the Authors 

Dr. Raj Shah, Director at Koehler Instrument Company, is a chemical engineer specializing in tribology, petroleum and fuels. Dr. Shah was also named an eminent engineer by Tau Beta Pi, the oldest engineering honor society in the U.S., a distinction reserved for individuals with remarkable technical achievements and exemplary character as well as being a member of IchemE, joining a global network of over 35,000 members. Further, he was elevated as a Fellow by the Chartered Management Institute (CMI), the world’s largest institution for management, and by the Institute of Measurement and Control (InstMC), the UK’s leading body for professionals in automation and control. He was recently inducted as a Fellow of the Royal Society of Chemistry (RSC), whose historic membership includes figures such as Newton and Einstein. Dr. Shah was named a Chartered Petroleum Engineer by the Energy Institute, a unique distinction. He has been recognized by ASTM International with multiple awards, including three Awards of Excellence, the Eagle Award, and the PM Ku and John A. Bellanti Sr. Memorial medals. Dr. Shah also serves as a volunteer adjunct professor at SUNY Stony Brook and has held advisory roles at several academic institutions. At Koehler Instrument Company, he oversees a thriving internship program which over the last 2 decades has had over 200 interns. He is currently an elected Fellow of ASTM, STLE, NLGI, AIC, RSC, InstMC, IChemE, CMI, and EI. Most notably, he is the only person in the global chemical industry to hold all six elite professional certifications: Certified Professional Chemist, Certified Chemical Engineer, Chartered Engineer, Chartered Chemist, Chartered Scientist, and Chartered Petroleum Engineer and has over 700 publications in a wide range of journals.

Ms. Kate Marussich, Mathew Stephen Roshan and Michael Lotwin are all Chemical and Molecular Engineering Undergraduate Students at Stony Brook University and interns at Koehler Instrument company, Holtsville, NY

4. References

[1] Chevron Phillips Chemical Company, “Polyalphaolefins,” https://www.cpchem.com/what-we-do/solutions/polyalphaolefins.
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[3] Maria J. G. Guimarey, Antía Villamayor, Enriqueta R. López, María J. P. Comuñas, “Performance and Antiwear Mechanism of 1D and 2D Nanoparticles as Additives to Polyalphaolephin” Nanomaterials, vol. 14, no. 13, p. 1101, 2024. https://doi.org/10.3390/nano14131101 
[4] H. Wang, Z. He, L. Xiong, L. Qian, L. Li, and Q. Long, “Investigating the Anti-Wear Behavior of Polyalphaolefin Oil with Methyl Silicon Resin Using Advanced Analytical Techniques” Lubricants, vol. 12, no. 12, p. 416, 2024. https://doi.org/10.3390/lubricants12120416 
[5] Holmberg, K., Erdemir, A. (2017). “Influence of tribology on global energy consumption.” Friction, vol. 5, 263–284. https://doi.org/10.1007/s40544-017-0183-5
[6] Kemipex. (2023). “Understanding the Properties and Uses of Polyalphaolefins”, https://www.kemipex.com/news/understanding-the-properties-and-uses-of-polyalphaolefins