Electrostatic Charging Due to Separation of Ions at Interfaces: Contact Electrification of Ionic Electrets

Abstract

This Review discusses ionic electrets: their preparation, their mechanisms of formation, tools for their characterization, and their applications. An electret is a material that has a permanent, macroscopic electric field at its surface; this field can arise from a net orientation of polar groups in the material, or from a net, macroscopic electrostatic charge on the material. An ionic electret is a material that has a net electrostatic charge due to a difference in the number of cationic and anionic charges in the material. Any material that has ions at its surface, or accessible in its interior, has the potential to become an ionic electret. When such a material is brought into contact with some other material, ions can transfer between them. If the anions and cations have different propensities to transfer, the unequal transfer of these ions can result in a net transfer of charge between the two materials. This Review focuses on the experimental evidence and theoretical models for the formation of ionic electrets through this ion-transfer mechanism, and proposes--as a still-unproved hypothesis--that this ion-transfer mechanism may also explain the ubiquitous contact electrification ("static electricity") of materials, such as organic polymers, that do not explicitly have ions at their surface.

Small-Scale Particle Interactions Are Having Significant Effects on Global Fluidized Bed Behavior

“…Pence et al (1994) and McCarty et al (2008) have noted the importance of water, and with it OH-ions, on the surface of particles for contact charging. Unless one prepares surfaces under ultra-high vacuum conditions, thin water layers are generally unavoidable.…”

Fundamental theories and basic principles of triboelectric effect: A review

“…The Poisson equation is dynamically verified from the fact that the triboelectric effect is a process in which charging and discharging are continuously coupled, and this relation is widely used in the particle triboelectric process simulation and analyses [2,37]. Following the thoughts of energy levels (including work function), for metal-dielectric-metal tribo-pairs (e.g., alkanethiol monolayer-coated Au(111 on Au) [38]), the main role of friction in electron transfer is to generate electron-hole pairs in mid-gap states near the Fermi surface (which explains why the work function is important) in normally insulating materials if they are in monolayer shape [38,39].…”

“…Even though the effective work function can be used to explain the metal-insulator tribo-pairs' electrification, in case of insulator-insulator tribo-pairs, electron transfer is often believed to be impossible [2]. As stated above, how to distinguish electron and/or ion transfer is important.…”

“…where 2 R demonstrates the quality of fit. Moreover, in metal-polymer cases, ion transfer can |www.Springer.com/journal/40544 | Friction http://friction.tsinghuajournals.com also be considered from the metal (mainly as donors) side.…”

“…In summary, the triboelectric effect is interesting but complex mainly due to the following reasons: (1) Even for a highly charged surface (namely 1 mC·m −2 ), the charge density can only achieve 1 electron unit per 10 5 surface atoms [1]. (2) Basic questions including which surface will be charged positively and which will have negative charges when two surfaces are brought into contact are still difficult to answer with certainty, and exceptions (i.e., cyclic triboelectric series) from different theories seem exclusive to each other [2]. (3) Multiple factors can work on the same triboelectric process, which adds to the complete analyses by decoupling each dominant parameter for modeling the triboelectric effect.…”