Triboelectric effect

The triboelectric effect (also known as triboelectric charging) is a type of contact electrification in which certain materials become electrically charged after they come into frictional contact with a different material, and are then separated.

The polarity and strength of the charges produced differ according to the materials, surface roughness, temperature, strain, and other properties.

It is therefore not very predictable, and only broad generalizations can be made. Amber, for example, can acquire an electric charge by contact and separation (respectively friction) with a material like wool.

Triboelectric effect is a general cause of every day’s electrostatics. The sign of the charges to be carried by a material depends on its relative polarity in comparison to the material to which it will contact.

Triboelectric effect is probably the only a few effects that have been known for thousands of years. Although this is one of the most frequently experienced effects that each and every one of us inevitably handles every day.

It is generally believed that after two different materials coming into contact, a chemical bond is formed between some parts of the two surfaces, called adhesion, and charges move from one material to the other to equalize their electrochemical potential. The transferred charges can be electrons or may be ions/molecules. When separated, some of the bonded atoms have a tendency to keep extra electrons, and some a tendency to give them away, possibly producing triboelectric charges on surfaces.

Materials that usually have strong triboelectrification effect are likely less conductive or insulators, thus, they usually capture the transferred charges and retain them for an extended period of time, building up the electrostatic charges, which are usually attributed to a negative effect in our daily life and technology developments.

We can use the following examples to illustrate the damages that can be caused by triboelectrification. Aircraft flying will develop static charges from air friction on the airframe, which will interfere with radio frequency communication. Electrostatic charges are an important concern for safety, due to the fact that it can cause an explosion and ignite flammable vapors. Carts/cars that may carry volatile liquids, flammable gasses, or explosive chemicals have to be discharged properly to avoid fire.

Some electronic devices, most notably complementary metal-oxide-semiconductor (CMOS) integrated circuits and MOSFET transistors, can be accidentally destroyed by a high-voltage static discharge that may be carried by gloves.

Therefore, triboelectrification is mostly taken as a negative effect in our daily life, industrial manufacturing, and transportation. Therefore, by surprise, although triboelectrification is known for thousands of years, it has not been used for many positive applications. It is until recently that the triboelectric effect has been widely used for converting mechanical energy into electricity and as self-powered active mechanical sensors.

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