What does this research mean for the field?

Formulating VG-32 mineral oil with 0.4 wt% SiO2 nanoparticles and oleic acid at a 1:3 ratio optimizes its thermal stability, increases thermal conductivity, and reduces the coefficient of friction by approximately 20% compared to the base oil. Novelty: ClaimNovelty.INCREMENTAL. Consensus alignment: ConsensusAlignment.NEUTRAL.

What question did this study set out to answer?

The aim is to formulate and evaluate oleic acid-stabilized SiO2 nanolubricants for improved lubrication properties.

May 17, 2026Open Access

Experimental Characterization of Oleic Acid–Stabilized SiO2 Nanolubricants for Enhanced Viscosity, Thermal, and Lubrication Performance of VG 32 Oil

Key Points

The aim is to formulate and evaluate oleic acid-stabilized SiO2 nanolubricants for improved lubrication properties.
Formulated SiO2-based nanolubricants using oleic acid in VG-32 mineral oil at varying concentrations (0.05–0.75 wt%)
Conducted sedimentation tests, zeta potential measurements, and viscosity assessments
Performed tribological evaluations using a block-on-ring tribometer.
The 0.4 wt% formulation showed a flash point of 226°C, which is a 6°C increase compared to base oil.
The incorporation of SiO2 NPs resulted in an 8.7% increase in thermal conductivity at 0.75 wt% concentration.
The 0.4 wt% SiO2 NLs achieved a ∼20% reduction in the coefficient of friction compared to base oil.

Abstract

As industrial machinery demands higher efficiency and reduced energy losses, nanolubricants (NLs) have emerged as promising next-generation tribological fluids for rotor bearing systems. The present study has formulated and evaluated SiO 2 -based NLs using oleic acid (OA) as a surfactant in VG-32 mineral oil, focusing on dispersion stability, rheological, thermal, and lubricity performance. SiO 2 nanoparticles (NPs) were incorporated at concentrations of 0.05–0.75 weight % (wt%) via a two-step process with OA at a 1:3 ratio. Sedimentation tests and zeta potential measurements confirmed good electrostatic stability, with values within ±30 mV. Temperature-dependent viscosity measurements revealed improved viscosity index and thermal-viscosity stability, with 1:3 OA surfactant coated formulations demonstrating superior performance over uncoated NLs. Thermal conductivity showed a progressive enhancement with SiO 2 NPs concentration, reaching a maximum of 8.7% at 0.75 wt% (0.135 W/m·K) compared to base oil (0.121 W/m·K). Flash and fire point measurements confirmed enhanced thermal safety, with the 0.4 wt% formulation achieving the highest fire point of 226°C, a 6°C improvement over the base oil. Tribological evaluation using a block-on-ring tribometer at a constant load of 100 lbf and speed of 60 rpm revealed that the 0.4 wt% SiO 2 NLs with 1:3 OA ratio achieved the lowest coefficient of friction (COF), representing ∼20% reduction over base oil, which is attributed to ball-bearing and mending effects at the contact interface. The coupled influence of zeta potential and NPs loading establishes a strong stability-performance relationship, supporting the development of energy-efficient nanolubricants for adjustable journal bearing systems.

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