Spin-selected electron transfer in liquid-solid contact electrification

Electron transfer has been proven the dominant charge carrier during contact electrification at the liquid-solid interface. However, the effect of electron spin in contact electrification remains to be investigated. This study examines the charge transfer between different liquids and ferrimagnetic solids in a magnetic field, focusing on the contribution of O₂ molecules to the liquid-solid contact electrification. The findings reveal that magnetic fields promote electron transfer at the O₂-containing liquid-solid interfaces. Moreover, magnetic field-induced electron transfer increases at higher O₂ concentrations in the liquids and decreases at elevated temperatures. The results indicate spin-selected electron transfer at liquid-solid interface. External magnetic fields can modulate the spin conversion of the radical pairs at the O₂-containing liquid and ferrimagnetic solid interfaces due to the Zeeman interaction, promoting electron transfer. A spin-selected electron transfer model for liquid-solid contact electrification is further proposed based on the radical pair mechanism, in which the HO₂ molecules and the free unpaired electrons from the ferrimagnetic solids are considered radical pairs. The spin conversion of the [HO₂• •e^-] pairs is affected by magnetic fields, rendering the electron transfer magnetic field-sensitive.

Microscale Bipolar Charge Distributions on Surfaces after Liquid Wetting and Evaporation in an Electric Field

Studies have shown that when insulator surfaces become electrostatically charged, complex spatial distributions of charge are produced, which are made up of micrometer-scale regions of both charge polarities. The origin of these charge patterns, often called "charge mosaics", is not understood. Here, we carried out controlled Kelvin force microscopy experiments on microfabricated interdigitated electrode systems to show that the process of wetting a surface by a liquid followed by evaporation of the liquid in an electric field can lead to neighboring micrometer-scale regions of positive and negative charge, which remain stable long after the electric field is removed. We thus suggest that local electric fields, perhaps due to the existing charge on the surface, can act in concert with liquid evaporation to contribute to the creation of charge mosaics.

Irreproducibility in the triboelectric charging of insulators: evidence of a non-monotonic charge versus contact time relationship

Contact electrification: irreproducibility of triboelectric charging magnitudes. Using Faraday pail measurements we show that a monotonous charging slope holds only left or right of a material-specific charge-peak point.

Humidity transforms immobile surface charges into mobile charges during triboelectric charging

Ionic material fragments created by contact stress will react with water to create ions that can transfer between surfaces.

Rubber Surface Change and Static Charging under Periodic Stress

Rubber materials play an important role in robotics, due to their sensing and actuating abilities, that are exploited in soft smart materials endowed with shape-adaptive and electroadhesive properties. The application of an electric field produces non-linear deformation that has been extensively modelled, but is not understood at the molecular level. The symmetric effect (the production of an electric field due to rubber deformation) was recently discovered and explained as follows: rubber surface chemical composition and adsorptive properties change during rubber deformation, allowing the surface to exchange charge with the atmosphere. The present work describes the complex surface morphology and microchemistry of tubing made from vulcanized natural rubber, showing that it is rough and made from two domain types: stiffer elevations containing Br or Al (depending on the sample used) and O, that rise above an elastic base that is exempt of elements other than C and H. The surface area fraction occupied by the elastic base is higher in the strained rubber than when it is relaxed. Electrostatic potential on rubber surfaces was measured as a function of the stretching frequency, using Kelvin electrodes and showing frequency-dependent potential variation. This is explained considering charge exchange between the atmosphere and rubber surface, mediated by water vapor adsorbed in the stretched rubber and trapped when it relaxes.

Advances in Solid-State Transformations of Coordination Bonds: From the Ball Mill to the Aging Chamber

Controlling the formation of coordination bonds is pivotal to the development of a plethora of functional metal-organic materials, ranging from coordination polymers, metal-organic frameworks (MOFs) to metallodrugs. The interest in and commercialization of such materials has created a need for more efficient, environmentally-friendly routes for making coordination bonds. Solid-state coordination chemistry is a versatile greener alternative to conventional synthesis, offering quantitative yields, enhanced stoichiometric and topological selectivity, access to a wider range of precursors, as well as to molecules and materials not readily accessible in solution or solvothermally. With a focus on mechanochemical, thermochemical and “accelerated aging” approaches to coordination polymers, including pharmaceutically-relevant materials and microporous MOFs, this review highlights the recent advances in solid-state coordination chemistry and techniques for understanding the underlying reaction mechanisms.

Stretchable Triboelectric Fiber for Self-powered Kinematic Sensing Textile

Stretchable fiber and yarn triboelectric nanogenerator are sought for such applications as wearable sensing system such as cloth communication devices, electronic textiles, and robotic sensory skin. Unfortunately, previously reported triboelectric fiber and yarn are difficult to have stretchable property. We introduce here a new type of stretchable and weavable triboelectric fibers with microdiameter dimensions. The stretchable triboelectric fibers can be reversibly stretched up to 50% in tensile direction while generating voltage output proportional to the applied tensile strain. The reversible distance change induced by the Poisson's ratio difference between the core fiber (silver-coated nylon/polyurethane) and the shell (wrinkled polyvinylidene fluoride-co-trifluoroethylene/carbon nanotube layer) during tensile deformation is the key working principle for electrical generation. Owing to exceptional structural stability, the stretchable triboelectric fibers show high performance retention after 10,000 times repeated stretching/releasing cycle. Furthermore, the stretchable triboelectric fibers are mechanically strong to be woven into a commercial textile for textile based sensors, which can detect magnitude as well as direction of the motion.

Topographically-designed triboelectric nanogenerator via block copolymer self-assembly

Herein, we report a facile and robust route to nanoscale tunable triboelectric energy harvesters realized by the formation of highly functional and controllable nanostructures via block copolymer (BCP) self-assembly. Our strategy is based on the incorporation of various silica nanostructures derived from the self-assembly of BCPs to enhance the characteristics of triboelectric nanogenerators (TENGs) by modulating the contact-surface area and the frictional force. Our simulation data also confirm that the nanoarchitectured morphologies are effective for triboelectric generation.

Mechanochemistry and sonochemistry: concluding remarks

This paper offers a perspective on mechanochemistry and offers summarizing commentary on the Faraday Discussion170, “Mechanochemistry: From Functional Solids to Single Molecules”. The connection between the mechanical and the chemical worlds dates back to our earliest written records and beyond, but its renaissance over the past decade or so has had an impact on a huge swathe of modern science and engineering: from metallurgists to polymer scientists to synthetic organic and inorganic chemists to cellular biologists. Connections among the different subfields of mechanochemistry (tribochemistry, trituration, macromolecular, and sonochemistry) are drawn out and the common themes and open questions are considered.

Friction, tribochemistry and triboelectricity: recent progress and perspectives

Mechanochemical reactions during polymer friction or contact produce ionic fragments distributed on positive and negative domains at both surfaces.