Abstract
Contact electrification (CE) involves a complex interplay of physical interactions in realistic material systems. For this reason, scientific consensus on the qualitative and quantitative importance of different physical mechanisms on CE remains a formidable task. The CE mechanism at a water/polymer interface is a crucial challenge owing to the poor understanding of charge transfer at the atomic level. First-principle density functional theory (DFT), used in the present work, proposes a new paradigm to address CE. Our results indicate that CE follows the same trend as the gap between the highest occupied and lowest unoccupied molecular orbitals (HOMO and LUMO) of polymers. Electron transfer occurs at the outmost atomic layer of the water/polymer interface and is closely linked to the functional groups and atom locations. When the polymer chains are parallel to the water layer, most electrons are transferred; conversely, if they are perpendicular to each other, the transfer of charges can be ignored. We demonstrate that a decrease in the interface distance between water and the polymer chains leads to CE in quantitative agreement with the electron cloud overlap model. We finally use DFT calculations to predict the properties of CE materials and their potential for triboelectric nanogenerator energy harvesting devices.
Highlights
Contact electrification (CE) is a well-known phenomenon describing how tribocharges are generated and distributed on contacting surfaces which is naturally present across all phases [1,2,3]
Our findings indicate that when water comes in contact with different polymers, electron transfer occurs almost exclusively at the water/polymer interface, and only the outmost layer of water contributes
The distance between the polymer and water surfaces is fixed to rule out the distance factor for the charge transfer (Figure 2(a))
Summary
Contact electrification (CE) is a well-known phenomenon describing how tribocharges are generated and distributed on contacting surfaces which is naturally present across all phases [1,2,3]. Two representative theoretical models have been established to obtain deeper insight into the charge transport: ion transfer and electron transfer between the contact interfaces [7,8,9,10,11,12,13]. Absorbed ions (such as OH-) are important for surface-charge transfer, typical results indicate that they are not strictly necessary [14, 15]. An electron cloud model was proposed by Wang’s group ( called a Wang transition) [3, 6, 16, 17] where the overlap of electron clouds between two atoms determines the strength of electron transfer between them. The electron transition model has a possible universal range of applicability yet its accuracy and reliability need further validation
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