Triboelectric Series

The triboelectric series is an important list of materials, which is created according to the tendency of materials to lose or gain electrons. The activity of electron transfer as a product of two bodies forming mutual contact with one another and the splitting is known as triboelectric charging. In such a process, one of the two bodies will always acquire electrons (negatively charged), and the remaining body will drop electrons (positively charged). The relative location of the two bodies on the triboelectric series will determine which body loses electrons, and which body gains electrons.

Triboelectric Effect

The triboelectric effect is a form of contact electrification in which certain substances become electrically activated after they are removed from a different substance with which they are linked. This process is called triboelectric charging. Rubbing two compact substances with each other intensifies the connection between their surfaces, creating the triboelectric effect. For example, brushing a glass with fur or combing hair with a plastic comb can accumulate triboelectricity. In fact, most of the familiar static electricity is fundamentally triboelectric in nature. The strength and polarity of the charges created vary according to the substances, temperature, strain, surface roughness and other characteristics.

The triboelectric effect is very volatile and unpredictable. In order to summarise the effect, only a broad generalisation can be made. Consider the example of amber; it can gain an electric charge through friction with a substance like wool. Thale of Miletus was the person to record this property. The term “electricity” was derived from the term “electra”, which came from the term “ēlektron” (amber). The prefix “tribo” means rub in Greek. Other instances of substances that can gain a significant charge when brushed together are hard rubber brushed with fur, and glass rubbed with silk.

The video explains the fundamentals of charging by induction

What is the Triboelectric Series

This series is a list of substances that is ordered by particular relevant characteristics, such as how fast a substance accumulates a charge relative to other substances on the list. Johan Carl Wilcke created the first triboelectric series list in 1757 (in his paper on static charges). Substances are generally listed according to the sequence of the polarity of charge separation when substances are touched by another body. A substance towards the base of the series, when touched with a substance which is placed near the top of the series list, will obtain more negative charges. The farther away the two substances are from each other on the list, the greater the charge transmitted. Substances close to each other on the list may not transact any charge or may even transact the contrast of what is suggested by the list. This result can be created by rubbing, oxides or contaminants, or other variables. Henniker and Shaw further extended the list by adding synthetic and natural polymers. They demonstrated the alteration in the order depending on environmental and surface conditions. Lists vary to some degree as to the required sequence of some substances since the relative charge changes for neighbouring substances. From real tests, there is slight or no quantifiable variation in charge affinity among metals, probably due to the quick motion of conduction electrons nullifying such differences.

Process of Triboelectrification

Interatomic interaction potential helps to comprehend the interaction between atoms. When two atoms are placed at equilibrium positions, with an ideal interatomic distance, the electron wave functions or clouds are partially overlapped. Somehow if the two atoms get near to each other as when shoved by an outside force, then the interatomic gap becomes smaller than the equilibrium distance. Thus, the two atoms repel each other as there is an increase in electron cloud overlap. It is in this area that electron transfer happens. In the other case, if two atoms are moved away from each other in a way that atoms have a greater interatomic length than equilibrium distance, they will surely attract each other due to Van der Waals force.

Applications of the Triboelectric Effect

• Sensors in smart clothing to measure vital signs
• Floors with a triboelectric layer connected to IoT devices
• Tactile sensors
• Shoes capable of monitoring physical exercise
• LED power supply
• Dust and particle sensors
• Autonomous sensors as forest fire detectors

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