Multiple timescale contact charging

Abstract

Contact charging between insulators is one of the most basic, yet least well understood, of physical processes. For example we have no clear theory for how insulators recruit enough charge carriers to deposit charge but not enough to discharge. In this letter we note that charging and discharging kinetics may be distinct, and from this observation we develop a mathematical model. The model surprisingly predicts that charging can decrease as contact frequency increases: we confirm this prediction experimentally and propose future steps.The most basic observation of static electrification, dating to William Gilbert's work in the 16 th century 1 , is that the materials that most readily acquire contact charge are insulators. We all know this: we get a shock when walking with rubber soles on a nylon carpet, on dry days when there are no free charge carriers to be found. Based on experiments with as many materials as he could lay his hands on, Gilbert termed materials that develop static charge "electrics:" silk, amber, glass and the like. These are what we today call insulators: materials that have no free charge carriers. This is undeniably very odd: if charges are bound, they should not transfer between materials, and if they are free they should conduct charges away. Insulators manage to mobilize sufficient free charges to transfer charge, but not enough to discharge. In this letter we focus on a particular, and revealing, feature of this oddity.

Understanding Contact Electrification at Water/Polymer Interface

“…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]. In spite of the long historical record, a detailed fundamental understanding of CE mechanisms, both extrinsic and intrinsic, remains indecisive [4][5][6].…”

“…Since the complex interplay of interactions usually refers to a diverse range of effects in real materials, CE can normally be placed in three categories: CE of metal-metal, metal-insulator, and insulator-insulator interfaces [1][2][3]6]. Previous studies suggest that CE for metal-polymer interfaces is susceptible not only to the values of the material energy gaps but also heavily affected by the interface distance, driving force, and contact stress at the contact region [18][19][20][21]; hence, it is still arduous to determine how electrons are transferred between polymers and other materials.…”

Precision measurement of tribocharging in acoustically levitated sub-millimeter grains

“…The buildup of charge due to repeated collisions between small particles is thought to be responsible for lightning in volcanic ash clouds 3 , the electrification of grains in sand storms 4 , and potentially also the very early stages of the formation of planetesimals from interstellar dust 5,6 . Several controlling parameters for particle charging have been measured, notably the effects of particle size 7,8 , atmospheric conditions and external electric fields 9,10 , surface hydrophobicity 11 , frequency of contact 12 , and kinetic energy prior to impact 13 . However, the underlying mechanism for charge exchange remains an area of debate, particularly between insulators, which have very low charge mobility.…”

Aggregation and pattern formation in charged granular gases

“…The experimental observation of the puzzling dynamics of charge sites on particle surface (Shinbrot et al , 2018), and considering that the surface structure of dielectric particles in practice can be irregular, point to the fact that the potential difference and exchange length are hardly deterministic. This part, i.e.…”