Scientists Identify Theoretical Maximum for Oil Viscosity

A new study published in the journal Physics of Fluids has established a theoretical ceiling for the viscosity of fluids, a discovery that highlights the extreme physical properties separating standard engine oils from geological materials. Professor Masaki Yoshida of Ritsumeikan University in Japan utilized geodetic data and rock-deformation experiments to pinpoint what he terms the “absolute cosmic limit” of viscosity.

The research calculates this upper limit at 10^30±2 pascal-seconds (Pa s). To provide context, water has a viscosity of roughly 10^-3 Pa s, while honey measures around 10¹ Pa s. A material reaching the cosmic limit would be so viscous that any perceptible flow would take longer than the current age of the Earth, effectively rendering the material rigid in practical terms.

While internal combustion engines rely on precise viscosity ratings to protect moving parts from friction and wear, these mechanical demands operate on a microscopic scale compared to the geological phenomena Yoshida studied. Motor oil viscosity is typically measured in millipascal-seconds, a unit that is one-thousandth of a pascal-second. The “weights” seen on consumer products are derived from indexing these measurements across various temperatures.

The findings stem from analyzing geological processes that unfold over millions of years, focusing on the flow of rock-forming minerals beneath the planet’s surface under intense heat. While automakers like Toyota Motor Corporation engineer lubricants to function within specific temperature ranges to ensure engine longevity, this study explores the physical boundaries of fluid dynamics far beyond the capabilities of any vehicle component.

What to watch

• Publication of related studies in Physics of Fluids.
• Advancements in synthetic lubricant formulations for automotive applications.

Source: original release