If you write with less force, it will be easier to slide the pencil on the paper.This is because the friction of graphite paper decreases.Nanoscale, however, a nanolapiz will require more force to slide it on a surface as the pressure decreases on it.This absolutely anomalous result was recorded by scientists at the National Institute of Standards and Technology of the United States (NIST).
Technically, the result shows a “negative coefficient of friction”, something that had never been seen before.Zhao Deng was researching graphite samples using the tip of an atomic force microscope.He was measuring the friction along the samples as they made the graphite stickier by adding oxygen atoms to its outermost layer – the lamellar graphite is a material formed by numerous sheets of graphene superimposed.
What Deng discovered is that when the adhesion strength between the upper layer and the graphite microscope tip becomes larger than the attraction of this first layer on the layer just below it generates a negative differential friction.
Overcoming the friction
Further analysis showed that the microscope tip pulls a small region of graphene out of graphite as a whole, forming a kind of “bubble”.And push this deformation on the surface requires more strength than doing the same on a smooth surface.
When the pressure increases from the tip, it pushes the bubble back to graphite, the friction decreases.The discovery is important for the fabrication of new nanoscale materials, and mechanical devices such as MEMS , NEMS micro and nano robots and nanomachines, for which overcome the friction is a major challenge.