Any material with a particle size less than 100 nanometers (0.1 micrometers) is defined as a nanoparticle.

When a material is reduced to the nanoscale, its reactivity increases significantly. This is primarily due to the increased surface area relative to its volume. As particle size decreases, the surface area increases, leading to a higher proportion of atoms being exposed and available for interaction with other substances.

This characteristic is especially important in the context of nano lubricants. Nanoparticles have an extremely high surface area-to-volume ratio, which enhances their ability to reduce friction and wear between surfaces.

Therefore, surface area, typically measured in square meters per gram (m²/g), is a critical parameter for evaluating the performance of a nano lubricant. The higher the surface area, the greater the lubricity and effectiveness of the nano lubricant.