Electric Field and Humidity Trigger Contact Electrification

Zhang, Yanzhen; Pähtz, Thomas; Y, Liu; Wang, Xiaolong; Zhang, Rui; Shen, Yang; Ji, Renjie; Cai, Baoping

doi:10.1103/physrevx.5.011002

Cited by 48 publications

(64 citation statements)

References 47 publications

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“…20 for more details about the apparatus. Note that the absence of an external electric field will also ensure that induction-based charging mechanisms 10,27,28 are not likely to be significant (see Supplementary Information). Particles in the raw videos were identified and tracked with the algorithm developed by Crocker and Grier 29 .…”

Section: Methodsmentioning

confidence: 99%

Direct observation of particle interactions and clustering in charged granular streams

et al. 2015

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Clustering of fine particles is of crucial importance in settings ranging from the early stages of planet formation [1][2][3] to the coagulation of industrial powders and airborne pollutants [4][5][6][7] . Models of such clustering typically focus on inelastic deformation and cohesion 1,4,6,8 . However, even in charge-neutral particle systems comprising grains of the same dielectric material, tribocharging can generate large amounts of net positive or negative charge on individual particles, resulting in long-range electrostatic forces [9][10][11] . The e ects of such forces on cluster formation are not well understood and have so far not been studied in situ. Here we report the first observations of individual collide-and-capture events between charged submillimetre particles, including Kepler-like orbits. Charged particles can become trapped in their mutual electrostatic energy well and aggregate via multiple bounces. This enables the initiation of clustering at relative velocities much larger than the upper limit for sticking after a head-on collision, a long-standing issue known from pre-planetary dust aggregation 1,12 . Moreover, Coulomb interactions together with dielectric polarization are found to stabilize characteristic molecule-like configurations, providing new insights for the modelling of clustering dynamics in a wide range of microscopic dielectric systems, such as charged polarizable ions, biomolecules and colloids [13][14][15][16] . One of the key difficulties in studying the interplay between repulsive contact forces, short-range cohesion and long-range electrostatic forces during cluster formation has been to obtain sufficiently detailed experimental data. Seeing how this process unfolds demands in situ observation of the collision trajectories among charged grains to extract quantitative information about their interactions. This requires the grains to be freed from gravity and tracked with high spatial and temporal resolution to capture individual collision events 17,18 . We overcome these obstacles with the set-up shown in Fig. 1a (refs 19,20). The granular material, in our experiments fused zirconium dioxide-silicate grains a few hundred micrometres in diameter, is contained in a vessel mounted inside a 3.0-m-tall cylindrical chamber. We evacuate this chamber to mitigate air drag. When a shutter covering a small orifice at the bottom of the vessel is opened, particles fall out freely, forming a dilute stream. Outside the chamber, a high-speed video camera falls alongside the grains, guided by low-friction rails. In the co-moving frame seen by the camera, the effect of gravity is eliminated, making it possible to track particle interactions in detail for about 0.2 s until the camera is decelerated by a foam pad. The same apparatus also allows determination of the net charge on individual grains: during free fall a horizontal electric field can be applied and the resulting horizontal acceleration observed by the camera gives the charge to mass ratio, q/m.Using particles with a narrow size d...

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Section: Methodsmentioning

confidence: 99%

Direct observation of particle interactions and clustering in charged granular streams

et al. 2015

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“…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.…”

Section: Introductionmentioning

confidence: 99%

Precision measurement of tribocharging in acoustically levitated sub-millimeter grains

Kline

Lim

Jaeger

2020

Review of Scientific Instruments

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Contact electrification of dielectric grains forms the basis for a myriad of physical phenomena. However, even the basic aspects of collisional charging between grains are still unclear. Here we develop a new experimental method, based on acoustic levitation, which allows us to controllably and repeatedly collide two sub-millimeter grains and measure the evolution of their electric charges. This is therefore the first tribocharging experiment to provide complete electric isolation for the grain-grain system from its surroundings. We use this method to measure collisional charging rates between pairs of grains for three different material combinations: polyethylene-polyethylene, polystyrene-polystyrene, and polystyrene-sulfonated polystyrene. The ability to directly and noninvasively collide particles of different constituent materials, chemical functionality, size, and shape opens the door to detailed studies of collisional charging in granular materials. arXiv:1910.09669v1 [cond-mat.soft]

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“…Zhang et al showed that when grains collide in the presence of an external field, the amount of exchanged charges does increase with the field strength [28]. Experimental results by Lee et al clearly show that polarization plays an important role in the collective dynamics of grains, even in the absence of an external field [29].…”

Section: Introductionmentioning

confidence: 99%

Field driven charging dynamics of a fluidized granular bed

et al. 2016

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A simplified model has previously described the inductive charging of colliding identical grains in the presence of an external electric field. Here we extend that model by including heterogeneous surface charge distributions, grain rotations and electrostatic interactions between grains. We find from this more realistic model that strong heterogeneities in charging can occur in agitated granular beds, and we predict that shielding due to these heterogeneities can dramatically alter the charging rate in such beds.

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Electric Field and Humidity Trigger Contact Electrification

Cited by 48 publications

References 47 publications

Direct observation of particle interactions and clustering in charged granular streams

Direct observation of particle interactions and clustering in charged granular streams

Precision measurement of tribocharging in acoustically levitated sub-millimeter grains

Field driven charging dynamics of a fluidized granular bed

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