Mimicking
the adhesion ability of animals using bio-inspired materials
and, consequently, the tuning of adhesion have aroused tremendous
research interest. In this study, we focus on the tuning of interfacial
adhesion of adhesive carbon nanotubes (CNTs) and their deformed state
(graphene) via an external electric field using first-principles calculations.
The results show that the adhesion energy of CNT or graphene almost
decreases linearly as the electric field changes from −0.2
to 0.2 V/Å. The variation of adhesion under the electric field
is further found to be closely related to contact electrification
as the negative fields facilitate interfacial charge transfer, and
the positive fields reduce charge transfer. Electronic behaviors are
further investigated to uncover the working mechanism of an external
electric field, which also explains the more sensitive responses of
contact electrification and hence adhesion in CNT systems compared
to graphene systems. It is further found that the external electric
field essentially changes the local work function of surfaces and
consequently modulates contact electrification and hence adhesion.
This study advances our understanding of adhesion and contact electrification
under an electric field and sheds light on the tuning of adhesion
of bio-inspired adhesive materials in engineering applications.
In this study, we investigate the contact electrification properties of glycine, cysteine, and dimethyl siloxane on silicon dioxide (SiO2) surfaces using density functional theory calculations. Molecule contacting through the sulfhydryl group has stronger adhesion to the SiO2-O and SiO2-OH surfaces. The SiOH/SiO2-Si system has the largest adhesion energy in all molecule/SiO2-Si contact systems and charge transfers from the molecule to the SiO2-O and SiO2-Si surfaces. The molecule/SiO2-OH systems have a reverse charge transfer direction. Molecules with their sulfhydryl and hydroxyl groups facing the SiO2-O and SiO2-OH surfaces have more transferred charges. The NH2/SiO2-Si system has a larger transferred charge than other molecule/SiO2-Si systems. The direction of charge transfer is determined by the Bader charge of the isolated surface atoms. The respective energy difference in the lowest unoccupied occupied molecular orbitals between contacting atoms influences the charge transfer. The respective energy difference in the highest occupied molecular orbitals reflects the electron attraction and affects charge transfer. Finally, the quantitative relationship between the transferred charge and energy gaps is established to evaluate the charge transfer. The findings propose a new perspective and in-depth understanding of contact electrification and shed light on the bio-inspired adhesive materials design and fabrication for engineering applications.
Contact electrification (CE) is a pretty common phenomenon, but still is poorly understood. The long-standing controversy over the mechanisms of CE related to polymers is particularly intense due to their complexity. In this paper, the CE between metals and polymers is systematically studied, which shows the evolution of surfaces accompanied by variations of CE outputs. The variations of CE charge are closely related to the creep and deformation of the polymer and metal surfaces. Then the relationship between CE and polymer structures is put forward, which is essentially determined by the electronegativity of elements and the functional groups in the polymers. The effects of load and contact frequency on the CE process and outputs are also investigated, indicating the increase of CE charge with load and frequency. Material transfer from polymer to metal is observed during CE while electrons transfer from metal to polymer, both of which are believed to have an influence on each other. The findings advance our understanding on the mechanism of CE between metal and polymers, and provides insights into the performance of CE-based application in various conditions, which sheds light on the design and optimization of CE-based energy harvest and self-powered sensing devices.
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