Charges at low conductivity

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Revision as of 22:39, 23 November 2008 by Nick (Talk | contribs) (Lightning)

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Ions will associate if they get closer than an energy that corresponds to -kT. <math>\text{ }E_{coul}=\frac{-e^{2}}{4\pi \varepsilon _{r}\varepsilon _{0}d}</math>
In water: <math>\varepsilon _{H_{2}O}\simeq 80\text{ and }d\gg 0.7nm</math>
In oil: <math>\varepsilon _{oil}\simeq 2\text{ and }d\gg 27nm</math>

In oil the electrostatic attraction is longer range than in water. In oil the “solvated” ion must be much larger than in water.

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Oil "Electrolytes"

The micelle core is highly polar. Possibly like a molten salt?
The diameters are 10’s of nanometers.
Single polymer molecules may be sufficient.

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Creation of charged micelles in oil

Micelles exchange ions with each other and with surfaces.

The equilibrium is a dynamic balance.


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Creation of charged surfaces in oil




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Electrical double layers in oil

The electrostatic repulsion is determined by Coulombic forces between the charged particles: <math>\Delta G^{R}=\frac{\pi D\varepsilon _{0}d^{2}\zeta ^{2}}{d+H}</math>

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Electric charges at low conductivity!!!

There is a great book on preview in Google Books called the Microphysics of Clouds and Precipitation that has a great chapter on cloud electricity.

The section 18.4 of the chapter talks about weakly charged clouds, and how the charges seem to be distributed over the volume of the cloud. One would expect that base of the cloud, since it is a poor conductor, would be negative, while the top would be full of positive ions; this actually ends up not being experimentally true in some cases, though this is not discussed in the book that I could find. Dr. Morrison did mention that depending on the nucleating particles there could be a charge variance in clouds of different geographical regions: has anyone found a reference for this?

The chapter then goes on to discuss the individual particles in the cloud, and how this distribution is varied in thunder clouds versus fair weather clouds. This was an interesting graph about the electric charges on differently sized drops and types of clouds, although not all of the supporting text is available online.

Looking over the book, I feel like the case for clouds being a form of Soft Matter. Does anyone have any thoughts on it?


I just checked out the interesting graph mentioned above, and thought the qualitative trends are quite clear, in that electrical charge per drop goes up with drop size following an approximate power-law; assuming all charges live on the surface and have a fixed density, then one would expect, as mentioned in the text, that the exponent of this power-law is close to 2; seems like some data shows a slightly weaker power-law. Quantitatively, though, I was curious to understand how much charge was really on the surface of these drops and how that might be interpreted in terms of charges per unit of surface. So what is an "e.s.u." or electrostatic unit?

Encyclopaedia Brittanica online gives the following definition: "If an electric force of one unit (one dyne) arises between two equal electric charges one centimetre apart in a vacuum, the amount of each charge is one electrostatic unit, esu, or statcoulomb. In the metre–kilogram–second and the SI systems, the unit of force (newton), the unit of charge (coulomb), and the unit of distance (metre), are all defined..." In terms of actual numbers for an esu, what does this mean?

One dyne is equivalent to 1E-5 Newtons. One centimeter is 1E-2 meters as we all know. All we have to do is plug these numbers into Coulomb's equation for electric forces in vacuum. We get that the charge of one esu is about 3.3E-10 coulombs, or roughly 2 billions electrons! Not a small number.

Now, if we look at some of that data... some of the lower numbers give about 1E-9 esus for a 10-micron droplet. That's only 2 electrons for the whole surface droplet. Really not that much, is it? Each electron can occupy an area of roughly 100 square microns on the surface. The higher data points for 10-micron droplets give almost 1E-6 esus, so about 1,000 electrons on the whole surface, or roughly 1 electron per square micron. That's a little bit more. The data points to the top right show 0.2esus for a 3000 micron diameter droplet, or about 10 electrons per square micron.

What do we make of all this? How might this variation in the surface charge density give us information on the droplet, its composition and/or history, or even physical properties?

I would think that the classification would depend very significantly on the drop density and mean temperature in the cloud. If we stick to the definition of "soft matter" having energy scales of order kT, an energy scale we can set would be the following. If the drop density is <math>n</math> and each drop has charge <math>q</math>, then the mean distance between drops is <math>d \approx n^{1/3}</math> leading to an electrostatic energy scale of <math>q^2/d^2 \approx q^2/n^{2/3}</math>. Thus it might make sense to require the drop charge and density to satisfy <math>q^2 \approx k T n^{2/3}</math>.

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Explosion in oil processing

Klinkenberg and van der Minne (1958)
“Early in 1954 a large tank in Shell’s refinery at Pernis exploded 40 minutes after the start of a blending operation in which a tops-naphtha mixture was being pumped into straight-run naphtha...

On the following day …again an explosion occurred 40 minutes …”

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"Static" Electricity

"Static" electricity is the accumulation of excess electric charge in a place with low electrical conductivity. Most people know of this excess charge because of what we can see (sparks) and hear when this charge is neutralized by contact with a conductor.

The phenomenon of "static" electricity was first known at least around 6th century BC, as discovered by Thales of Miletus. Thales thought objects can change to become other objects, such as water into earth (obviously wrong on this). Even though he did not know what static electricity was, Thales did address the topic, approaching it through magnets and amber, which attracted when electrified by rubbing. Scientific interest in this topic started from this point on.

Research into the subject began when machines were able to create electricity, e.g. friction generator developed by Otto von Guericke in the 17th century. Furthermore, the connection between static electricity and storm clouds was famously demonstrated by Benjamin Franklin in 1750. Most famously, Michael Faraday in 1832 published the results of his experiment on the electric charges. Although at the time, physics world thought this "static electricity" was different that other electric charge, Faraday proved that the electricity induced using a magnet, voltaic electricity produced by a battery, and static electricity were all the same. From this point on, branch of science studying static electricity merged with the study of electricity in general.

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Potential dangers with "static" electricity

The buildup of static electric charge can be damaging, especially in small electric devices. In these, force acting on the charge can cause breaking elements in the circuit. Therefore, a lot of manufacturers produce anti-static devices to prevent this behavior.

Also, discharge of static electricity can create serious hazards in industries dealing with flammable materials. In these cases, single electrical spark may ignite explosive mixtures. In a similar manner, charge can possibly build up, discharge and ignite fuel during pumping gas.

Finally, in outer-space, due to low humidity environment, large amounts of static charge can accumulate and potentially damage sensitive equipment.

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Common Misconceptions on "Static Electricity

For more detailed description go to this website(it's fun to read!):

  • 'Static Electricity' is electricity which is static? → No.Electrostatics is not about "staticness," instead it's about charge and forces.
  • Electric circuits have nothing to do with static electricty? → Wrong. Electric currents are caused by voltage, and the voltage in a circuit is caused by the imbalances of charge which are present on the surface of the metal wires. "Static electricity" is what makes circuits operate! Without the "static electricity" supplied by batteries or generators, modern electrical devices could not exist.
  • Friction causes 'static electricity?' → Wrong. Static electricity appears whenever two dissimilar insulating materials are placed into intimate contact and then separated again.
  • 'Static electricity' has nothing to do with High Voltage? → Wrong. Everyday "static electricity" involves immense voltages. The tiniest "static spark" is caused by about 1000 volts. Longer "car door sparks" and "doorknob sparks" can involve as much as 10,000 volts.
  • 'Static electricity' is a buildup of electrons? → Not exactly. It is not a buildup of anything, it is an IMBALANCE between quantities of positive and negative particles which existed beforehand.
  • Neutral objects have no charge? → Not quite. Electric charge is the major component of all atoms. Therefor matter is made out of canceled electric charge.
  • 'Charging' a capacitor fills it with charge? → No. 'Charged' and 'Uncharged' capacitors actually contatain equal amounts of charge.
  • We don't use 'Static electricity,' it's too weak and feeble? → Not exactly.
  • 'Static' is a useless and rare event? → Not really. "Static electricity" is important in many other places besides lightning, photocopiers, and doorknob sparks. For example, your muscles are driven by long-chain molecules which are forced to slide across each other. Also nerves function as tiny capacitors, with charge pumps to electrify them, and ion gates to discharge them.
  • Clouds are charged by rubbing together? → No.
  • Ben Franklin's kite was struck by lightning? → No. He just showed that a kite would collect a tiny bit of electric charge out of the sky during a thunderstorm.
  • Electrostatics" is the study of electricity at rest? → No.

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