Contact electrification and the triboelectric effect are complex processes for mechanical-to-electrical energy conversion, particularly for highly deformable polymers. While generating relatively low power density, contact electrification can occur at the contact–separation interface between nearly any two polymer surfaces. This ubiquitousness of surfaces enables contact electrification to be an important phenomenon to understand energy conversion and harvesting applications. The mechanism of charge generation between polymeric materials remains ambiguous, with electron transfer, material (also known as mass) transfer, and adsorbed chemical species transfer (including induced ionization of water and other molecules) all being proposed as the primary source of the measured charge. Often, all sources of charge, except electron transfer, are dismissed in the case of triboelectric energy harvesters, leading to the generation of the “triboelectric series”, governed by the ability of a polymer to lose, or accept, an electron. Here, this sole focus on electron transfer is challenged through rigorous experiments, measuring charge density in polymer–polymer (196 polymer combinations), polymer–glass (14 polymers), and polymer–liquid metal (14 polymers) systems. Through the investigation of these interfaces, clear evidence of material transfer via heterolytic bond cleavage is provided. Based on these results, a generalized model considering the cohesive energy density of polymers as the critical parameter for polymer contact electrification is discussed. This discussion clearly shows that material transfer must be accounted for when discussing the source of charge generated by polymeric mechanical energy harvesters. Thus, a correlated physical property to understand the triboelectric series is provided.

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researchers aim to magnify the triboelectric charge on polymer surfaces. Polymer triboelectrification can be enhanced in several ways, including surface functionalization, [8] adjustment of the electronic and physicochemical properties between contacting materials, [9][10][11][12][13][14][15] or by increasing the specific contact area via nanostructuring. [16,17] Surface contact electrification can be observed also in nature. Spider ballooning is one of the most exciting natural phenomena. Using electrified strands of silk, [18] spiders can travel in the airstream for distances of hundreds of kilometers. [19] Spider silk is electrified due to contact and friction with airborne particles or during the spinning process. [20] To ensure the electrostatic flight, holding the weight of a spider, even in the absence of any aerodynamic lift, a strong surface charge is required.To understand how silk achieves this strong surface charge, understanding of its macromolecular structure is required. Spider silk has a hierarchical structure composed of highly ordered macromolecular inclusions which are interconnected by disordered elastomeric chains. [21] This macromolecular structure may lead to stress concentration, which we hypothesize is (partially) responsible for the strong surface charge.Recently, it has been found that the surface electrification of polymers is strongly connected to their physicochemical Triboelectrification of polymers enables mechanical energy harvesting in triboelectric generators, droplet generators, and ferroelectrets. Herein, triboelectric polymers, inspired by the ordering in spider-silk, with strongly enhanced contact electrification are presented. The ordering in polyether block amide (PEBA) is induced by the addition of inorganic goethite (α-FeOOH) nanowires that form H-bonds with the elastomeric matrix. The addition of as little as 0.1 vol% of α-FeOOH into PEBA increases the surface charge by more than order of magnitude (from 0.069 to 0.93 nC cm -2 ). The H-bonds between α-FeOOH and PEBA promote the formation of inclusions with higher degree of macromolecular ordering, analogous to the structure of spider silk. The formation of these inclusions is proven via nanoindentation hardness measurements and correlated with H-bond-induced chemical changes by Fourier transform infrared spectroscopy and direct scanning calorimetry. Theoretical studies reveal that the irregularity in hardness provides stress accumulation on the polymer surface during contactseparation. Subsequent molecular dynamic studies demonstrate that stress accumulation promotes the mass-transfer mechanism of contact electrification. The proposed macromolecular structure design provides a new paradigm for developing materials for applications in mechanical energy harvesting.

Here we demonstrate the approach for improving the triboelectric charge in contact-separation of identical PDMS contact layers by three orders of magnitude. It is achieved by functionalization with self-assebled monolayers...