Spontaneous tribocharging of similar materials

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Spontaneous tribocharging of similar materials

Post by Cr6 on Tue Feb 03, 2015 12:19 am

July 2008 EPL,83(2008) 24004
www.epljournal.org

Spontaneous tribocharging of similar materials

T. Shinbrot, T.S.Komatsu and Q. Zhao
Department of Biomedical Engineering, Rutgers University - Piscataw
ay, NJ 08854, USA

Abstract

– We investigate the spontaneous triboelectrification of similar materials. This effect, first reported in 1927, has been little studied but is easily reproduced. We find in two separate experimental systems, where materials are prepared in the same way and rubbed symmetrically, that symmetry breaking occurs so that one material becomes positive and the other negative.

Curiously, the distribution of charges on the materials appears to be self-similar, with different charge patterns on the positive and the negative surface. We propose a mechanism in which an initial localized charge may spawn the production of smaller localized charges of the same polarity.

Copyright c©EPLA, 2008

Introduction. –

It has been recognized since the 16th century [1,2] that insulators (originally termed “electrics”) can readily be charged by rubbing or contact, while conductors (“non-electrics”) are more difficult to charge. Careful experiments have shown this effect to be distinct from the ability of conductors to carry acquired charges to ground [3]. Thus PTFE —one of the best insulators known— is the material of choice to produce mega- Volt potentials in Van de Graaf generators. This is paradoxical since insulators lack free charge carriers, and it has remained unexplained to this day how they recruit these charges. The paradox has been compounded by experiments first performed in the 1920s [4] and later rigorously repeated [5,6] that demonstrate that even identical insulators can transfer charges during rubbing. In one sense, this should come as little surprise, since charge is also generated through contact between identical materials in the best known electrification system: atmospheric lightning. Similarly, large charges are acquired by aeolian transport of desert sands, which have little to rub against beyond other sand [7–9]. It is troublesomely unclear how insulators in general acquire the free charges that they convey during tribocharging, and how identical insulators in particular can charge one another at all We note that because the two disks are of the same size and roll without slipping with the same speed, local regions come into repeated contact against one another, and so we can examine local, as well as global, charging of the disks. We do this by isolating two regions from the data record, one positive and one negative on each disk, as identified in fig. 2(b) in cyan and magenta rectangles. We show the averages of voltages within these regions as a function of time in correspondingly colored insets in fig. 2(c). Evidently locally as well as globally, charged regions consistently retain their polarity and increase their magnitude over time.

The results of these two experiments are surprising, both because it is unclear what provokes the symmetry breaking seen and because the very act of symmetry breaking works against the apparent electrostatic gradient imposed by Coulomb’s law, which ought to oppose the motion of positive (negative) charges to the more electro- positive (-negative) surface. To analyze the effect, we next quantify the spatial and temporal distributions of acquired charges, which we do in three ways.
...

Discussion. –

We have shown in two examples —first using common latex balloons rubbed by hand, and second using instrumented polycarbonate disks rotated with step- per motors— that similar materials can tribocharge when symmetrically rubbed against one another, despite lacking either an obvious source for charge carriers or an apparent triboelectric gradient to drive the charge transfer. We have found both by quantitative measurement of voltage as a function of distance and by qualitative examination of the patterns on charged balloons that the charges that accu- mulate appear to be complex and may be consistent with a recursive, self-similar, model for charge formation, a result supported by power spectral analysis of the disk experi- ment. We have proposed and confirmed by direct simula- tion that once a fixed spot of charge forms on an insulating surface, an oppositely charged halo appears to catalyze the downstream formation of smaller clusters of similar charge to the original spot. We have conjectured that this may be the source of the positive self-similar charge distributions seen. The negative charge distributions (fig. 4(b)) could in this scenario be Lichtenberg discharge patterns formed by the discharge of the free negative ions produced by the model (fig. 4(c)).

Although only speculative at this stage, the hypothesis that positive spots generate more positive spots and liberate free negative ions appears to explain many of the observations seen in natural and laboratory tribocharging. In particular, this hypothesis suggests that the mechanism of triboelectric charging may be intrinsically unstable, so that very small variations in surface charges, geometry or chemistry may tend to become amplified. Thus, a single charge on a surface may become an engine for the generation of like charges. The notion that charges may generate more charges of the same sign is counterintuitive, however the phenomena that we seek to understand are themselves inexplicable without some such mechanism, and we propose that this first hypothesis may serve as a catalyst for more rigorous testing.

(more at link: http://coewww.rutgers.edu/~shinbrot/Web2009/PdfFiles/Balloon.pdf )

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Re: Spontaneous tribocharging of similar materials

Post by LongtimeAirman on Fri Feb 06, 2015 11:48 pm

Cr6, Thanks for the posting, relatively simple experimental findings on a basic electromagnetic subject - tribocharging. I always thought it was just static electricity.

By applying contact and motion pressure, then releasing (or breaking contact), between insulating materials (laytex balloons or polycarbonate disks are described in this paper), positive and negative charge distributions are created on the material surfaces, seemingly at random, and with possible fractal qualities. Charge tends to increase to a limit after repeated contacts. There doesn’t seem to be any like sign repulsion effect in charge accumulation. Different colored toners attracted to the charged surfaces provide detailed images of the charge distribution. Washing the materials and repeating the experiment yields a new charge distribution pattern. Positive areas may appear more as spots, while negative charge may appear more as streaks. Branched patterns can occur. Charging occurs in the presence of an “atmosphere” and not in an inert gas. And more that I cannot say I understand.

Reviewing Wiki: http://en.wikipedia.org/wiki/Triboelectric_effect , It’s long been known that contact between various materials yield varying charge strengths. “John Carl Wilcke published the first triboelectric series in a 1757 paper on static charges”. Tribocharging, though not well understood, is explained by making and breaking molecular chemical bonds between insulating materials. “After coming into contact, a chemical bond is formed between parts of the two surfaces, called adhesion, and charges move from one material to the other to equalize their electrochemical potential”. It’s not clear to me whether there’s supposed to be a conservation of charge. Repeated contact/friction, low humidity and cold conditions can cause high voltages and often lead to the strongest static discharges. For comparison, consider; “From actual tests, there is little or no measurable difference in charge affinity between metals, probably because the rapid motion of conduction electrons cancels such differences.”

I thought just electrons were involved, but “Equalizing electrochemical potential”, doesn’t sound electron exclusive. Miles might ridicule the idea of chemical bonding; who but he knows? To be fair, the experimenters considered airborne ions as a possible necessary condition. Still, the experimental results provided data that cannot be adequately explained, even considering the wiki definition. The results demand further study and discussion. The Standard Theory falls short. But we already know that.

Does Miles explain electrostatics? I haven't seen electrostatics mentioned. Can we add the charge field to the experimental discussion to lead to better understanding? I’m certain of it. Lloyd has asked me to explain positive and negative charge behavior beyond apparent attraction a la Miles several times. I’ve been stumped but I’ve been thinking about it.

Briefly rub two balloons together. Several times. Starting from the Unified Field - both gravity and the charge field are present. Neglect the earth’s gravity and E/M fields, leaving just the earth’s charge field. We are working with two different material objects; setting them in motion and contact against each other in our living room. We know that the earth’s charge field is a veritable sea of photons raising from the earth’s surface. All objects themselves emit their own charge fields; ghostly, compared to the earth’s, as each electron, proton and neutron recycles photons they receive from the earth, roughly 18 times their mass in photonic matter each second in the case of the proton. The balloons’ contacted surfaces have a higher energy level. They recycle slightly more charge, appear less ghostly, and they can spark.

An electrostatic (or electromagnetic) field can only manifest in the presence of ions and electrons. We know from experience that dragging our feet on a rug (another two different materials rubbing together) will result in sparks. Electrons are displaced by the contact, motion and release actions. Two electron possibilities come to mind:

1. Some surface electrons positions are striped vacant. Some ions become exposed. The charge field channel flow rate at electron vacancies is increased, presenting increased charge emission (repulsion) at charge channel exits and increased “attraction” at charge channel entrances. Both attraction and repulsion here are due to charge field “flow” direction.

2. The brief, higher energy “pressing” interval - allows some excess electrons to group together in various numbers expressed by John Wilcke's table. I imagine some charge flow inputs being clogged with clumps of electrons. When the two surfaces are close, large electron aggregates can quickly respond to charge channel direction changes to fill many charge channel entrances. Given enough time, I believe the electrons will sort themselves out. Of course, Miles hasn’t addressed electron matter either, other than citing Ken Shoulder’s work.

My neck is out there. Please chew.

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Re: Spontaneous tribocharging of similar materials

Post by Cr6 on Sat Feb 07, 2015 2:04 am

LongtimeAirman wrote:Cr6, Thanks for the posting, relatively simple experimental findings on a basic electromagnetic subject - tribocharging. I always thought it was just static electricity.
....
 Two electron possibilities come to mind:

1. Some surface electrons positions are striped vacant. Some ions become exposed. The charge field channel flow rate at electron vacancies is increased, presenting increased charge emission (repulsion) at charge channel exits and increased “attraction” at charge channel entrances. Both attraction and repulsion here are due to charge field “flow” direction.

2. The brief, higher energy “pressing” interval - allows some excess electrons to group together in various numbers expressed by John Wilcke's table. I imagine some charge flow inputs being clogged with clumps of electrons. When the two surfaces are close, large electron aggregates can quickly respond to charge channel direction changes to fill many charge channel entrances. Given enough time, I believe the electrons will sort themselves out. Of course, Miles hasn’t addressed electron matter either, other than citing Ken Shoulder’s work.

My neck is out there. Please chew.

Thanks for the extended reply LTAM.  That is along the lines of what I was thinking as well. "Simple Experiment" with unexpected results that can't be reconciled with most "electron-QT" theories. I like your "clumping" theory because that follows the experiments logically. The need for "dust" and "dust clouds" to create "charge" indicates to me that these "clouds" are shaping Mathis' charge field. The atoms-molecules are recycling charge via "particulate matter in a cloud" in a way that "ionizes" it due to the way the Charge Field flows through it. 

This quote:


Now let us develop the mass of the photon from another direction, and compare that number with the number we found from G and 1821. The energy of a photon is around 10-19 J, which, using the equation E = mc2, gives us a mass equivalence of 1.11 x 10-36 kg. That is within a factor of 4 of the mass we found by the first method, as you see. To make the correction, we just use a slightly less energetic photon. Photons have a range of energies, so this is easy to do. What kind of photon matches our first prediction exactly? A photon with a mass equivalence of 2.77 x 10-37 kg, or an energy of 2.5 x 10-20J, which is a frequency of 3.77 x 1013/s, which is an infrared photon.

An infrared photon has a mass equivalence that is 1.66 x 10-10 smaller than the proton mass. Which means the proton is 18213 more massive than the infrared photon. Is this a coincidence? No. For one thing, the infrared photon is the most common photon, being a large part of the emission from the sun as well as majority of molecular motion. Yes, molecules vibrate in the infrared, for the most part.

http://milesmathis.com/photon.html

If one really digs into various defintions of "friction" and "Chemical-bonding" it gets rather murky very quickly. What "rubs" against what to create charge? Is it chemically related or something else (ala Charge Field).  There is enough specific incongruent phenomena around this to make it "center stage". I think Mathis' theories at least give clues into how this works. Tesla used large and long rotating cotton bands to create enormous charges from ambient air via a Triboelectric process.  I really think the current accepted theory for this is not sufficient to explain most of the phenomena.   I agree that Mathis and Ken Shoulder's give a bit more to chew on theoretically... especially Shoulder's "Electron Ensembles":



The triboelectric effect is related to friction only because they both involve adhesion. However, the effect is greatly enhanced by rubbing the materials together, as they touch and separate many times. For surfaces with differing geometry, rubbing may also lead to heating of protrusions, causing pyroelectric charge separation which may add to the existing contact electrification, or which may oppose the existing polarity. Surface nano-effects are not well understood, and the atomic force microscope has enabled rapid progress in this field of physics.
https://en.wikipedia.org/wiki/Electrochemical_potential

Also:

"Saturation", or maximum charge that can be transferred: Beyond a certain amount of charge transferred, additional friction energy (rubbing) does not produce any additional charging. Apparently, two effects limit the amount of charge per area that can be transferred. If the spark E-field (10 KV/cm) is exceeded, the two surfaces will spark to each other (after being separated from each other by at least about 1 mm), reducing the charge transferred below 10 KV/cm. This maximum charge per area is about Q/A = 1 nC/cm2, from this formula. A second, lower charging limit seems to apply to surfaces with an affinity difference of < (about) 50 nC/J. Two materials that are this close to each other in the triboelectric series never seem to reach a charge difference as high as 2 nC/cm2, no matter how much they are rubbed together. Although not yet fully verified, it is proposed that the maximum Q/A (in nC/cm2) is roughly 0.02 x the difference in affinities (in nJ/C) if the two materials are within 50 nC/J of each other. Surfaces that cannot reach spark potential obviously cannot spontaneously dump charge into the air. This is therefore a good reason to select contacting materials such that their affinity difference is small.

Inaccurate information about air being "positive", etc.-- A triboelectric series table has been circulating on the internet, and it contains various inaccuracies. Though attribution is rarely given, it appears to be mostly from a 1987 book. It lists air as the most positive of all materials, polyurethane as highly negative, and various metals being positive or negative, apparently based on their known chemical electron affinities, rather than on electrostatic experiments. (From actual tests, there is little or no measurable difference in charge affinity between different types of metal, possibly because the fast motion of conduction electrons cancels such differences.) In gaseous form, air is generally unable to impart any charge to or from solids, even at very high pressure or speed. If chilled to a solid or liquid, air is expected to be slightly negative, not positive. There are three cases where air can charge matter (in the absence of external high voltage). 

1. If contaminated by dust, high-speed air can charge surfaces, but this charge comes from contact with the dust, not the air. The charge polarity depends on the type of dust.
2. If air is blown across a wet surface, negative ions are formed due to the evaporation of water. In this case, the wet surface charges positive, so the air becomes negative.
3. If air is hot (above about 1000°C), it begins emitting ions (both + and -.) This is thermal in nature, not triboelectric.

http://www.trifield.com/content/tribo-electric-series/

Electron Ensembles

http://blog.hasslberger.com/2007/10/ken_shoulders_evos_exotic_vacu.html

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