Editing Triboelectric effect (section)

== Basic characteristics ==
Triboelectric charging occurs when two materials are brought into contact then separated, or slide against each other. An example is rubbing a plastic pen on a shirt sleeve made of cotton, wool, polyester, or the blended fabrics used in modern clothing.<ref>{{Citation |title=A Plastic Comb Rubbed With a Cotton Cloth Attracts Small Pieces of Paper | date=6 September 2012 |url=https://www.youtube.com/watch?v=rtl9TyMZSP8 |access-date=2023-09-05 |language=en}}</ref> An electrified pen will attract and pick up pieces of paper less than a square centimeter, and will repel a similarly electrified pen. This repulsion is detectable by hanging both pens on threads and setting them near one another. Such experiments led to the theory of two types of electric charge, one being the negative of the other, with a simple sum respecting signs giving the total charge. The electrostatic attraction of the charged plastic pen to neutral uncharged pieces of paper (for example) is due to induced [[dipole]]s<ref name=":16" />{{Rp|location=Chapter 27}} in the paper.

The triboelectric effect can be unpredictable because many details are often not controlled.<ref>{{Cite journal |last1=Lowell |first1=J. |last2=Akande |first2=A. R. |date=1988 |title=Contact electrification-why is it variable? |url= https://iopscience.iop.org/article/10.1088/0022-3727/21/1/018 |journal=Journal of Physics D: Applied Physics |volume=21 |issue=1 |pages=125–137 |doi=10.1088/0022-3727/21/1/018 |bibcode=1988JPhD...21..125L |s2cid=250782776 |issn=0022-3727}}</ref> Phenomena which do not have a simple explanation have been known for many years. For instance, as early as 1910, Jaimeson observed that for a piece of cellulose, the sign of the charge was dependent upon whether it was bent concave or convex during rubbing.<ref name=":8">{{Cite journal |last=Jamieson |first=Walter |date=1910 |title=The Electrification of Insulating Materials |journal=Nature |volume=83 |issue=2111 |page=189 |doi=10.1038/083189a0 |bibcode=1910Natur..83..189J |s2cid=3954491 |issn=0028-0836|doi-access=free }}</ref> The same behavior with curvature was reported in 1917 by Shaw,<ref name=":19" /> who noted that the effect of curvature with different materials made them either more positive or negative. In 1920, Richards pointed out that for colliding particles the velocity and mass played a role, not just what the materials were.<ref name=":6">{{Cite journal |last=Richards |first=Harold F. |date=1920 |title=Electrification by Impact |url= https://link.aps.org/doi/10.1103/PhysRev.16.290 |journal=Physical Review |volume=16 |issue=4 |pages=290–304 |doi=10.1103/PhysRev.16.290 |bibcode=1920PhRv...16..290R |issn=0031-899X}}</ref> In 1926, Shaw pointed out that with two pieces of identical material, the sign of the charge transfer from "rubber" to "rubbed" could change with time.<ref name=":7">{{Cite journal |last=Shaw |first=P. E. |date=1926 |title=Electrical separation between identical solid surfaces |journal=Proceedings of the Physical Society |volume=39 |issue=1 |pages=449–452 |doi=10.1088/0959-5309/39/1/344 |bibcode=1926PPS....39..449S |issn=0959-5309}}</ref>

There are other more recent experimental results which also do not have a simple explanation. For instance the work of Burgo and [[Ali Erdemir|Erdemir]],<ref name=":12">{{Cite journal |last1=Burgo |first1=Thiago A. L. |last2=Erdemir |first2=Ali |date=2014 |title=Bipolar Tribocharging Signal During Friction Force Fluctuations at Metal–Insulator Interfaces |url= https://onlinelibrary.wiley.com/doi/10.1002/anie.201406541 |journal=Angewandte Chemie International Edition |volume=53 |issue=45 |pages=12101–12105 |doi=10.1002/anie.201406541|pmid=25168573 }}</ref> which showed that the sign of charge transfer reverses between when a tip is pushing into a substrate versus when it pulls out; the detailed work of Lee ''et al.''<ref>{{Cite journal |last1=Lee |first1=Victor |last2=James |first2=Nicole M. |last3=Waitukaitis |first3=Scott R. |last4=Jaeger |first4=Heinrich M. |date=2018 |title=Collisional charging of individual submillimeter particles: Using ultrasonic levitation to initiate and track charge transfer |url= https://link.aps.org/doi/10.1103/PhysRevMaterials.2.035602 |journal=Physical Review Materials |volume=2 |issue=3 |page=035602 |doi=10.1103/PhysRevMaterials.2.035602 |arxiv=1801.09278 |bibcode=2018PhRvM...2c5602L |s2cid=118904552 |issn=2475-9953}}</ref> and Forward, Lacks and Sankaran<ref name="Shinbrot 2008 24004">{{Cite journal |last1=Shinbrot |first1=T. |last2=Komatsu |first2=T. S. |last3=Zhao |first3=Q. |date=2008 |title=Spontaneous tribocharging of similar materials |url= https://iopscience.iop.org/article/10.1209/0295-5075/83/24004 |journal=EPL (Europhysics Letters) |volume=83 |issue=2 |page=24004 |doi=10.1209/0295-5075/83/24004 |bibcode=2008EL.....8324004S |s2cid=40379103 |issn=0295-5075}}</ref> and others measuring the charge transfer during collisions between particles of [[zirconia]] of different size but the same composition, with one size charging positive, the other negative; the observations using sliding<ref name="Shinbrot 2008 24004" /> or [[Kelvin probe force microscope]]<ref name=":9" /> of inhomogeneous charge variations between nominally identical materials.
[[File:Asperities charged.svg|thumb|Illustration of triboelectric charging from contacting asperities|upright=1.5]]

The details of how and why tribocharging occurs are not established science as of 2023.  One component is the difference in the [[work function]] (also called the [[electron affinity]]) between the two materials.<ref name=":4">{{Cite journal |last=Harper |first=W. E. |date=1951 |title=The Volta effect as a cause of static electrification |url=https://royalsocietypublishing.org/doi/10.1098/rspa.1951.0019 |journal=Proceedings of the Royal Society of London. Series A. Mathematical and Physical Sciences |volume=205 |issue=1080 |pages=83–103 |bibcode=1951RSPSA.205...83H |doi=10.1098/rspa.1951.0019 |issn=0080-4630 |s2cid=110618773}}</ref> This can lead to charge transfer as, for instance, analyzed by Harper.<ref name=":2">{{Cite book |last=Harper |first=W. R. |title=Contact and frictional electrification |date=1998 |publisher=Laplacian Press |isbn=1-885540-06-X |oclc=39850726}}</ref><ref name=":13" /> As has been known since at least 1953,<ref name=":1">{{Cite journal |last=Vick |first=F.A.|date=1953 |title=Theory of contact electrification |url= https://iopscience.iop.org/article/10.1088/0508-3443/4/S2/301 |journal=British Journal of Applied Physics |volume=4 |issue=S2 |pages=S1–S5 |doi=10.1088/0508-3443/4/S2/301 |bibcode=1953BJAP....4S...1V |issn=0508-3443}}</ref><ref>{{Cite journal |last=Castle |first=G. S. P. |date=1997 |title=Contact charging between insulators |url= https://linkinghub.elsevier.com/retrieve/pii/S0304388697000090 |journal=Journal of Electrostatics |volume=40–41 |pages=13–20 |doi=10.1016/S0304-3886(97)00009-0}}</ref><ref>{{Cite journal |last=Bailey |first=Adrian G. |date=2001 |title=The charging of insulator surfaces |url= https://linkinghub.elsevier.com/retrieve/pii/S0304388601001061 |journal=Journal of Electrostatics |volume=51–52 |pages=82–90 |doi=10.1016/S0304-3886(01)00106-1}}</ref><ref>{{Cite journal |last=Schein |first=L. B. |date=2007 |title=Recent Progress and Continuing Puzzles in Electrostatics |url= https://www.science.org/doi/10.1126/science.1142325 |journal=Science |volume=316 |issue=5831 |pages=1572–1573 |doi=10.1126/science.1142325 |pmid=17569848 |s2cid=136500498 |issn=0036-8075}}</ref> the contact potential is part of the process but does not explain many results, such as the ones mentioned in the last two paragraphs.<ref name=":8" /><ref name=":7" /><ref name=":12" /><ref name=":9" /> Many studies have pointed out issues with the work function difference ([[Volta potential]]) as a complete explanation.<ref>{{Cite thesis |last=Elsdon |first=R. |url= https://www.repository.cam.ac.uk/items/41c4ca4e-53ba-451f-9e4d-f9f7e6cd5c2e |title=Fundamental and applied aspects of contact electrification |type=PhD |publisher=University of Cambridge |date=1975 |doi=10.17863/CAM.16064}}</ref><ref>{{Cite journal |last1=Akande |first1=A. R. |last2=Lowell |first2=J |date=1987 |title=Charge transfer in metal/polymer contacts |url= https://iopscience.iop.org/article/10.1088/0022-3727/20/5/002 |journal=Journal of Physics D: Applied Physics |volume=20 |issue=5 |pages=565–578 |doi=10.1088/0022-3727/20/5/002 |bibcode=1987JPhD...20..565A |s2cid=250812629 |issn=0022-3727}}</ref><ref name=":17">{{Cite journal |last1=Kok |first1=Jasper F. |last2=Lacks |first2=Daniel J. |date=2009 |title=Electrification of granular systems of identical insulators |url= https://link.aps.org/doi/10.1103/PhysRevE.79.051304 |journal=Physical Review E |volume=79 |issue=5 |page=051304 |doi=10.1103/PhysRevE.79.051304 |pmid=19518446 |arxiv=0902.3411 |bibcode=2009PhRvE..79e1304K |s2cid=2225090 |issn=1539-3755}}</ref><ref name=":28">{{Cite journal |last1=Galembeck |first1=Fernando |last2=Burgo |first2=Thiago A. L. |last3=Balestrin |first3=Lia B. S. |last4=Gouveia |first4=Rubia F. |last5=Silva |first5=Cristiane A. |last6=Galembeck |first6=André |date=2014 |title=Friction, tribochemistry and triboelectricity: recent progress and perspectives |url= http://xlink.rsc.org/?DOI=C4RA09604E |journal=RSC Adv. |volume=4 |issue=109 |pages=64280–64298 |doi=10.1039/C4RA09604E |bibcode=2014RSCAd...464280G |issn=2046-2069}}</ref> There is also the question of why sliding is often important. Surfaces have many nanoscale [[Asperity (materials science)|asperities]] where the contact is taking place,<ref name=":18">{{Cite book |last1=Bowden |first1=Frank Philip |title=The friction and lubrication of solids |last2=Tabor |first2=David |date=2001 |publisher=Clarendon Press |orig-date=1950 |isbn=978-0-19-850777-2 |edition=Repr |series="Oxford Classic Texts" series |location=Oxford}}</ref> which has been taken into account in many approaches to triboelectrification.<ref name=":2" /> [[Alessandro Volta]] and [[Hermann von Helmholtz]] suggested that the role of sliding was to produce more contacts per second.<ref name=":13">{{Cite journal |last=Harper |first=W. R. |date=1961 |title=Electrification following the contact of solids |journal=Contemporary Physics |volume=2 |issue=5 |pages=345–359 |doi=10.1080/00107516108205281 |bibcode=1961ConPh...2..345H |issn=0010-7514}}</ref> In modern terms, the idea is that electrons move many times faster than atoms, so the electrons are always in equilibrium when atoms move (the [[Born–Oppenheimer approximation]]). With this approximation, each asperity contact during sliding is equivalent to a stationary one; there is no direct coupling between the sliding velocity and electron motion.<ref>{{Cite journal |last1=Born |first1=M. |last2=Oppenheimer |first2=R. |date=1927 |title=Zur Quantentheorie der Molekeln |journal=Annalen der Physik |language=de |volume=389 |issue=20 |pages=457–484 |doi=10.1002/andp.19273892002|bibcode=1927AnP...389..457B |doi-access=free }}</ref> An alternative view (beyond the Born–Oppenheimer approximation) is that sliding acts as a quantum mechanical pump which can excite electrons to go from one material to another.<ref name=":11">{{Cite journal |last1=Alicki |first1=Robert |last2=Jenkins |first2=Alejandro |date=2020 |title=Quantum Theory of Triboelectricity |url= https://link.aps.org/doi/10.1103/PhysRevLett.125.186101 |journal=Physical Review Letters |volume=125 |issue=18 |page=186101 |doi=10.1103/PhysRevLett.125.186101 |pmid=33196235 |arxiv=1904.11997 |bibcode=2020PhRvL.125r6101A |s2cid=139102854 |issn=0031-9007}}</ref> A different suggestion is that local heating during sliding matters,<ref>{{Cite journal |last1=Liu |first1=Guangming |last2=Liu |first2=Jun |last3=Dou |first3=Wenjie |date=2022 |title=Non-adiabatic quantum dynamics of tribovoltaic effects at sliding metal–semiconductor interfaces |url= https://linkinghub.elsevier.com/retrieve/pii/S2211285522001185 |journal=Nano Energy |volume=96 |page=107034 |doi=10.1016/j.nanoen.2022.107034|arxiv=2112.04687 |bibcode=2022NEne...9607034L |s2cid=247006239 }}</ref> an idea first suggested by Frenkel in 1941.<ref>{{Cite journal |last=Frenkel |first=J. |date=1941 |title=On the electrification of dielectrics by friction |journal=Journal of Physics-USSR |volume=V |issue=1 |pages=25–29}}</ref> Other papers have considered that local bending at the nanoscale produces voltages which help drive charge transfer via the [[Flexoelectricity|flexoelectric]] effect.<ref name=":5">{{Cite journal |last1=Mizzi |first1=C. A. |last2=Lin |first2=A. Y. W. |last3=Marks |first3=L. D. |date=2019 |title=Does Flexoelectricity Drive Triboelectricity? |url= https://link.aps.org/doi/10.1103/PhysRevLett.123.116103 |journal=Physical Review Letters |volume=123 |issue=11 |page=116103 |doi=10.1103/PhysRevLett.123.116103 |pmid=31573269 |arxiv=1904.10383 |bibcode=2019PhRvL.123k6103M |s2cid=128361741 |issn=0031-9007}}</ref><ref name=":26" /> There are also suggestions that surface or trapped charges are important.<ref>{{Cite journal |last1=Fukada |first1=E. |last2=Fowler |first2=J. F. |date=1958 |title=Triboelectricity and Electron Traps in Insulating Materials: Some Correlations |url= https://www.nature.com/articles/181693b0 |journal=Nature |volume=181 |issue=4610 |pages=693–694 |doi=10.1038/181693b0 |bibcode=1958Natur.181..693F |s2cid=4269111 |issn=0028-0836}}</ref><ref>{{Cite journal |last1=Guerret-Piecourt |first1=Christelle |last2=Bec |first2=Sandrine |last3=Treheux |first3=Daniel |date=2001 |title=Electrical charges and tribology of insulating materials |url= https://linkinghub.elsevier.com/retrieve/pii/S1296214701012185 |journal= Comptes Rendus de l'Académie des Sciences, Série IV |volume=2 |issue=5 |pages=761–774 |doi=10.1016/S1296-2147(01)01218-5|arxiv=0707.2649 |bibcode=2001CRASP...2..761G }}</ref> More recently there have been attempts to include a full solid state description.<ref>{{Cite journal |last1=Pan |first1=Shuaihang |last2=Zhang |first2=Zhinan |date=2017 |title=Triboelectric effect: A new perspective on electron transfer process |url= https://pubs.aip.org/jap/article/122/14/144302/144925/Triboelectric-effect-A-new-perspective-on-electron |journal=Journal of Applied Physics |volume=122 |issue=14 |page=144302 |doi=10.1063/1.5006634 |bibcode=2017JAP...122n4302P |issn=0021-8979}}</ref><ref name=":39">{{Cite journal |last1=Olson |first1=Karl P. |last2=Mizzi |first2=Christopher A. |last3=Marks |first3=Laurence D. |date=2022 |title=Band Bending and Ratcheting Explain Triboelectricity in a Flexoelectric Contact Diode |url= https://pubs.acs.org/doi/10.1021/acs.nanolett.2c00107 |journal=Nano Letters |volume=22 |issue=10 |pages=3914–3921 |doi=10.1021/acs.nanolett.2c00107 |pmid=35521939 |arxiv=2201.04688 |bibcode=2022NanoL..22.3914O |s2cid=245906054 |issn=1530-6984}}</ref><ref>{{Cite journal |last1=Willatzen |first1=Morten |last2=Lin Wang |first2=Zhong |date=2018 |title=Theory of contact electrification: Optical transitions in two-level systems |url= https://linkinghub.elsevier.com/retrieve/pii/S2211285518305780 |journal=Nano Energy |volume=52 |pages=517–523 |doi=10.1016/j.nanoen.2018.08.015|bibcode=2018NEne...52..517W |s2cid=106380058 }}</ref><ref name=":11" />