Triboelectric generator materials

Besides the previously mentioned piezoelectric material, the second one lies in electret that can preserve the induced charges for a long time. It can not only be used in the fabrication of piezoelectric generators but also triboelectric generators based on electrostatic induction effect. The electret and related devices are discussed further. Here we mainly focus on PVDF and its copolymers in polymer based-piezoelectric transducer/generator. 

Tribocharging is the process of electricity generation when two different materials rub against each other. Some materials easily give up or accept electrons from other materials imder friction. The tri-boelectric series lists materials that give up electrons in order from easiest to hardest. For many materials, the dielectric constant determines the position of that material in the triboelectric series. The further apart the two materials are that rub against each other, the more charge is transferred. 

The presence of dispersed fillers in the polymer material in low amounts may intensify electrization, increase the residual charge and change the friction coefficient. Introduction of the filler in the electret state exerts a still stronger effect on polymer electrization on frictional interaction with metals. Depending on the direction of the field intensity vector formed by the filler particles, the field generated by triboelectrization can be attenuated or intensified. This means that the principle of the electret-triboelectrization superposition is realized [49], which can be used to regulate the parameters of frictional interactions. Thus, by the introduction of the electret filler, e.g. mechanically activated F-3 powder, it is possible to decrease the friction force (Fig. 4.9). 

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