Triboelectric charging of insulating polymers–some new perspectives

Abstract

A nanowire based triboelectric nanogenerator for harvesting water wave energy and its applications APL Materials 5, 074104 (2017) Tribolectric charging results from contact between surfaces, but precisely what is meant by each is not defined or understood, as they relate to charging. The recent microscopic evidence that contact charging can result from material transfer provides incentive to examine how contact charging is affected by these two factors. It is suggested that vigorous rubbing or pressing of two polymers results in transfer of deeper layers than would result from light contacts. Different layers can have substantially different compositions because polymers are typically not homogeneous as a function of depth, so contact and surface are related in this way. This could account for charge transfer between identical polymers, especially in asymmetric contacts in which the frictional force on one polymer differs from that on the other, so that material from different depths is transferred. This review outlines the roles of physics, chemistry and surface analysis in sufficient detail to focus on these subjects. It also makes suggestions how these concepts could be applied to some of the current leading edge research in this area.

Fundamental theories and basic principles of triboelectric effect: A review

“…The intensive research has cast light on some triumphing trend explanation for the above triboelectric series. It has been confirmed that polymers having strong tendencies to charge positively have high dielectric constants, and are highly polar and hydrophilic [29]. For example, it is found that polymers with oxygen functional groups (more polar) will be charged more positively than those with nitrogen functional groups [36].…”

“…This is mainly because there may exist charge backflow when the contact surfaces are dynamically moving farther or closer, and this is a natural process if the capacitive configuration shown in Fig. 1 is considered [29]. Second, the driving force of the tribo-contacts would not completely contribute to the final surface charge density, as triboluminescence may play a role and consume some of the energy [6,12].…”

“…Material transfer to cause charging is believed to occur when vigorous rubbing or pressing is introduced [29,51]. For example, when some polymers are rubbed with friction, an exchange of deeper layer materials occurs [52].…”

“…For example, when some polymers are rubbed with friction, an exchange of deeper layer materials occurs [52]. (This helps explain why even the same polymers can be charged by tribo-contacts; it is because even identical polymers will have different material compositions at each depth, which account for the same material charge transfer [29].) Moreover, material transfer is possible if dynamical changes in the surfaces and tribological environments exist, because materials will tend toward a lower potential energy state and these dynamical changes can lead to the potential energy minimum shifts [53,54].…”

“…Humidity and acidity have obvious significance owing to their strong effects on surface electrical conductivity and capacitance configuration (for example, the charge leakage required to achieve a dynamical balance in the triboelectric effect will be affected [1]; in real applications, salts including quaternary ammonium [29] can then be used as the charge control agent) [79,80].…”