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I took apart my cooling platform Something like this :Cooling Platform

And I found something like this inside :

Canyon of dust 1 Canyon of dust 2 Canyon of dust 3

I wonder why around the hollows are the "canyon like" structures.

PS: I also drop this platform on the floor, maybe this could be a reason ?

EDIT :

Everybody seems (except Brandon Enright answer) to ignore the word "dust" in this question. Those structures are not in the plastic itself. It is dust ON the plastic.

Proof :

Dust canyon

Completely wiped out with my finger :

Dust canyon wiped

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  • $\begingroup$ Is it really dust (i.e., can you wipe it away) because it looks like stress cracks in the plastic. $\endgroup$ – Kyle Kanos Oct 16 '13 at 18:47
  • $\begingroup$ Very intriguing pictures. Whatever those are, I would also love an explanation $\endgroup$ – kleingordon Oct 16 '13 at 18:57
  • $\begingroup$ Is the fan suctioning the air out or throwing the air in?Plus it seems to be around the round circular cavity.It may be that a vortex of air and dust formd in these depressions.The dust could charge electrostatically while moving in the vortex.When you stop the device the charged dust may be settling on in chanels previously ionised on the plastic.It looks similar to ionisation channels when lightning occurs.The lightning will always follow the same ionisation channel. $\endgroup$ – Chappy May 13 '17 at 8:26
  • $\begingroup$ Would the same/similar pattern form if the casing was metallic ie conducting and not made of plastic? $\endgroup$ – Chappy May 25 '17 at 18:03
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I've seen this too. The circles that the "dust canyons" are around are marks from the injection molding process. Specifically, they're the ejector pin marks made when the pins push the part out of the mold. The force of pushing the part out probably creates radial stress cracks in the grain of the plastic. If you use a microscope to look at the surface of the plastic you'll probably see a rougher patch in the shape of those canyon lines and that's what dust is clinging on to.

There are a lot of different types of injection molding defects. Splay marks are a similar feature of injection molding that could look like your image.

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    $\begingroup$ There's a lot of "probably" here. Speculation does not constitute an answer. I mean no offense. $\endgroup$ – Wossname May 9 '17 at 18:20
  • $\begingroup$ @Wossname on the other hand, how much of physics are we absolutely sure on? If that's the criteria, we have no answers about anything. $\endgroup$ – Asher May 15 '17 at 15:57
  • $\begingroup$ In the linked question patterns are visible which are not associated with the ejector pin marks.The ejection process may act as a precipitating factor. $\endgroup$ – Chappy May 16 '17 at 5:52
  • $\begingroup$ @Asher, I completely agree but, existentialism aside, it is still possible to apply our scientific method to a question. $\endgroup$ – Wossname May 21 '17 at 13:32
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These kind of braching structures can form by Diffusion-limited-aggregation (DLA). The way this works is that little particles of dust clumps wander at random (due to Brownian motion) until they hit another particle and then stick together.

If you simulate the DLA process on a computer by placing a particle at the center and then introducing particles at random places around the edges of the screen and allow them to move according to Brownian Motion and and stick to eachother when they hit, then you get these branching structures that look like they have "fingers" coming out of them.

So why don't these structures just accumulate and look like a circular ink blot with irregular edges? Why are they branched?

This is because of a positive feedback loop. When a bump appears by chance it pokes out beyond the rest, so there is a higher chance that other brownian particles will hit it. So the bump will grow even faster.

If you look at this image you will see that it would be very hard for a randomly moving particle to avoid all the branches and hit the center (the dark blue area). Thus the fingers get longer and longer. enter image description here

So why would these form at the canyons?

As seen in the image of the duplicate question these branching structures don't only form at the circular canyons. They form around the other edges of the injection-moulding features too, because the surface allows the small particles to latch on at these irregularities and stick to the plastic. Even if only a few particles manage to latch on there it will grow by the rules of the DLA process.

So is this really how these structures formed?

Just by visual similarity we can't prove that this is really how these structures formed. There are actually many different processes that can generate the same patterns. One method if we wanted to see if we can rule out DLA would be to look at the fractal dimension of this structure. The fractal dimension is a measure of how densely packed the branches are and in DLA processes the clusters are fractals with a dimension of about 1.71.

DLA can be observed in many systems such as electrodeposition, Hele-Shaw flow, mineral deposits, and dielectric breakdown.

When comparing the pictures of the same question that was just posted recently, one cannot be sure that in these two cases these patterns were formed by the same process. It seems plausible, but it doesn't have to be. enter image description here enter image description here

If you look at bacterial colonies they can have branching structures as the ones pictured above. enter image description here(This image is from this paper)

By varying the growth conditions of bacteria one can achieve a great range of different branching structures. Below a certain nutrient concentration for example one can achieve these branching structures. Although these structures may look similar to DLA structures, they grow very differently. They are dependent on the food available, bacterial reproduction and the movement of the bacteria. The bacteria can even communicate by emitting chemicals that guide their direction of motion.

The reasons why they accumulate at the craters could be very similar, namely that organic particles and humidity that the bacteria grow on aggregate at the irregularities.

Any comments, edits, calculations and experiments are very much appreciated. I think it should be possible to figure out exactly how these structures formed with more input from the community.

I asked on the Biology StackExchange here to figure out if we can rule out that it is a bacterial colony or if that is a possibility.

Much of this answer is informed by this book on branching structures by Philip Ball.

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    $\begingroup$ I think DLA is a great candidate for what is happening. The wikipedia entry gives the example of Hele-Shaw flow for a process that leads to DLA. It is for flow between two parallel plates with a (infinitely) small gap between them; which would be a good approximation for what happens in these fan cases. $\endgroup$ – JMac May 15 '17 at 11:13
  • $\begingroup$ Much better answer than mine! $\endgroup$ – Brandon Enright May 19 '17 at 2:18
  • $\begingroup$ +1 This is a great bit of research. Now the "ejector pin marks" on the plastic make sense as "seed" points for the pattern, the slight glitches in the plastic surface are a place that particles moving in Brownian motion might be more likely to collide with and attach to. Absolutely fascinating. $\endgroup$ – Wossname May 21 '17 at 13:43
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Further to the answers that refer to stress "cracks":

It is also possible that, in the absence of any actual physical crack, the stresses imposed on the plastic could have changed the electrostatic properties of the plastic. This in turn could alter how dust collects on the plastic, making the changes visible.

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They seem to be Lichtenberg patterns. Quote "After discharging a high voltage point to the surface of an insulator, he recorded the resulting radial patterns by sprinkling various powdered materials onto the surface. By then pressing blank sheets of paper onto these patterns, Lichtenberg was able to transfer and record these images, thereby discovering the basic principle of modern xerography." https://en.m.wikipedia.org/wiki/Lichtenberg_figure

It seems that some how the plastic which is a dielectric is getting stressed by high voltage.The source of the voltage stressing it would have to be investigated.It may be that whirling around of dust in a vortex which gets charged due to triboelelectric effect may be causing this.Then when the device is switched off...the dust would settle over firming the Lichtenberg pattern. Further reference can be found here

https://books.google.co.in/books?id=TVpMXfBkX40C&pg=PA1&lpg=PA1&dq=lichtenberg+patterns+xerography&source=bl&ots=sOzdu3B8v8&sig=nvwUlmumxExfnRyA5-NXXy_v2Po&hl=en&sa=X&ved=0ahUKEwiZmaWTv-zTAhUKqo8KHVZGAVkQ6AEIODAE#v=onepage&q=lichtenberg%20patterns%20xerography&f=false

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  • $\begingroup$ The book from the link above tells about the electrograph by which patterns made by atmospheric electricity on a surface were made visible. $\endgroup$ – Chappy May 13 '17 at 9:27
  • $\begingroup$ From the Wikipedia. "A lightning strike can also create a large Lichtenberg figure in grass surrounding the point struck. These are sometimes found on golf courses or in grassy meadows.[12] Branching root-shaped "fulgurite" mineral deposits may also be created as sand and soil is fused into glassy tubes " $\endgroup$ – Chappy May 13 '17 at 9:38
  • $\begingroup$ Again quoting from the Wikipedia "there is also a marked difference in the form of the figure, according to the polarity of the electrical charge that was applied to the plate. If the charge areas were positive, a widely extending patch is seen on the plate, consisting of a dense nucleus, from which branches radiate in all directions. Negatively charged areas are considerably smaller and have a sharp circular or fan-like boundary entirely devoid of branches. Heinrich Rudolf Hertz employed Lichtenberg dust figures in his seminal work proving Maxwell's electromagnetic wave theories." $\endgroup$ – Chappy May 13 '17 at 9:42
  • $\begingroup$ Here's a video I found of something similar done at the fermi lab. The reason is high voltage no doubt but how it comes about has to be investigated. youtu.be/9lHxBQvqlaU $\endgroup$ – Chappy May 13 '17 at 11:24
  • $\begingroup$ See also the linked question, where a similar effect was observed in a device with no fans. $\endgroup$ – Emilio Pisanty May 13 '17 at 11:58
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Have you ever spilled a soft drink on it? Or any other liquid with sugar?

If so, it could be that something is actually in your cooling platform. If it has condensed in there, it could be that when you set your computer on it, it heats up enough to cause the substance to leak out a little. Those circles may also have some sort of epoxy (if something didn't leak in from the outside.)

The vibrations from the fans running could have caused them to spread into those fractal-like structures, from there the dust may have been stuck into the sticky substance.

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  • $\begingroup$ Those circles are the result of the molding process when manufactured. The cracks are more likely related to stress than to sugary drinks. $\endgroup$ – Kyle Kanos Oct 16 '13 at 20:05
  • $\begingroup$ the user still hasn't verified they are cracks. $\endgroup$ – codeAndStuff Oct 16 '13 at 20:25
  • $\begingroup$ You are suggesting that a spilled drink managed to stay only at these "canyons" (and not get everywhere) but make those patterns after repeated heating with help from vibrations. The seems unreasonable to me, especially considering injection molding defects. $\endgroup$ – Kyle Kanos Oct 17 '13 at 15:29
  • $\begingroup$ Initially I guess I didn't read the problem carefully enough to realize that these were inside of the shell rather than outside. Had this been the case, he could have wiped the outside and some residue remained inside that eventually leaked out. Simply misunderstood the question. I don't contend that it is much more likely that these effects are due to the manufacturing process and/or propagating stress fractures. $\endgroup$ – codeAndStuff Oct 17 '13 at 15:43
  • $\begingroup$ Those are not crack, Wait minute I will provide photos. $\endgroup$ – Paul Brewczynski Oct 17 '13 at 20:11
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Polymers have an amorphous structure and a crystalline structure.In reality both these phases exist in between each other.The interfacial region between the two are where charges separation occurs called Maxwell Wagner Interfacial Polarization. https://books.google.co.in/books?id=Ta04BQAAQBAJ&pg=PA23&lpg=PA23&dq=maxwell+wagner+effect+amorphous+crystalline+interface&source=bl&ots=ijnUsqOKET&sig=GUHgpyPMO7mG1_l6aHZcVEf_0Fg&hl=en&sa=X&ved=0ahUKEwjXns6pjfHTAhXLLo8KHX2GAd8Q6AEIRTAI#v=onepage&q=maxwell%20wagner%20effect%20amorphous%20crystalline%20interface&f=false Hence charges already exist separated wuthin the plastic. Application of pressure at the time of ejecting the piece would lower the dielectric strength of the plastic at the surface radial to the applied pressure. These charges would be free to migrate closer to the surface which would act to attract dust over the areas of static charge.

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