Talk:Diffusion

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rated top as high school/SAT biology content - tameeria 14:30, 17 February 2007 (UTC) - Also: Concentration gradient redirects here - tameeria 19:28, 22 February 2007 (UTC)

The article could need an expansion on diffusion in biological systems. The current diffusion across biological membranes section is just a list of bullet points. - tameeria 17:59, 18 February 2007 (UTC)

Contents


[edit] Mathematics

It is to specialistic for the general reader looking up diffusion.145.116.1.3 (talk) 07:45, 5 June 2008 (UTC)


[edit] General discussion

Diffusion is the movement from a high to low concentration along the concentration gradient. In ternary solutions particles can be tranported from low to high concentrations. Joao

This can happen in binary alloys, too Olof

Diffusion as noted in the last paragraph generally implies a dilution or mixing of the medium. Hence I'm not totally happy by a contrast with radiation as this is itself a diffusion mechanism. Indeed the reference to heat through a window is indeed diffusion by radiation. Rjstott

Heat through a window was a bad example. Maybe heat through a window at nighttime was what I was thinking. Perhaps heat through an oven door is a better example. However, I think its correct to say radiation and diffusion are completely different transport phenomena: in heat transport by radiation, photons get emitted by thermal activation and carry the energy until the photons are absorbed somewhere else. heat transport by diffusion is governed by the thermal conductivity of the material and the temperature gradient. Olof

Way back in school, there were three heat transport mechanisms, conduction, convection and radiation. I believe that heat can be diffused by any of these three. Light is an electromagnetic radiation and diffusion is often associated with light too. Perhaps an example based on light diffusion might work better? Rjstott

You are right about the three mechanisms: Radiation is when photons carry the energy from one place to another. Heat disappears from a material when the photon gets created, and reappears at the place where the photon gets absorbed. The key part there is that the material needs to be hot enough so that it can thermally activate a photon creation, as when a metal is 'red hot'. Of course, at lower temperatures, the photons are lower energy and there is some radiative heat transport. Convection is when, for example, the hot air next to the oven rises to the ceiling, and the air that used to be near the ceiling moves to.... and so on. It is only applicable to fluids. Conduction is when heat diffuses through a material, and it is the only one of the three mechanisms which is strictly a diffusion. By this I mean that the mathematical equation which is used to model the heat flow is the diffusion equation. Olof

I was also thinking of adding a section on computer graphics diffusion: the process whereby an image is blurred by an image editing program also follows the same math. Olof

[edit] Disambiguation

I hate it when one page is used for two topics. Something needs to be done! Either create a page for Diffusion (physics) and Diffusion (anthropology) or kill the anthropology on the diffusion page.

Osmosis= diffusion of water not general diffusion surely. Equally my GCSE biology teacher could have been lying to me...

I agree the osmosis reference should be removed, and I did so. Danrs 18:45, 15 August 2007 (UTC)

[edit] Types of diffusion in separate pages

I just made a major change to the layout of the page. Since there were alot different types (and sub-types) of diffusion listed inthe article, I grouped them all in one section and moved the relevant information to separate pages on the particular types of diffusion. Hope that made the page a bit clearer than before. Cheers Karol 18:01, 15 September 2005 (UTC)

[edit] Diffusion and Turbulence

I think diffusion is not connected to turbulence, the example of smoke dissipating into the air is a bad example since it involves convection. I have removed the parts accordingly. Lirnup 20:28, 28 September 2005 (UTC)

Good work catching that. Also, diffusion isn't quite the same thing as Brownian motion, no? Karol 06:06, 29 September 2005 (UTC)
As I understand it, in the case of diffusion the particles move one by one by brownian motion, but I'm not really an expert on that. Lirnup 06:21, 29 September 2005 (UTC)
Sure, in the case of the diffusion of particles, but that is only one type of diffusion since not only particles diffuse. There is also the subtle difference that BM is a description of the stochastic motion of single particles in itself, whereas diffusion is more a dsecription of a process, in which there is a net transport and flux of the diffusing quantity (related to some kind of gradient). Karol 14:37, 29 September 2005 (UTC)
Yes, the brownian motion thing came in only to make a kind of juxtaposition. We better take this out there Lirnup 10:28, 4 October 2005 (UTC)

[edit] A redlink story

At 11h04 today (31 october 2005), I added a link to collective diffusion in this article. At 11h06, or 2 minutes later, this link was deleted by user:Karol Langner, on the basis that I should first create the collective diffusion article (I created this article "only" at 11h17). So Karol, a question: are you going to delete all the red links that have existed for more than 2 minutes in this encyclopedia, or should I conclude that you are specifically after my edits? ThorinMuglindir 12:32, 31 October 2005 (UTC)

OK sorry Karol I was a bit upset when I dscovered you had canceled my edit. Now, admit the real reason why you canceled it is because it conflicted with yours, and having to cope with those 2 text boxes is a mess. So that you thought that since your edit as big and mine was just a link, it wouldn't be much of a deal for me to add it back... I prefer that to you being specifically after my edits. ThorinMuglindir 14:27, 31 October 2005 (UTC)

BTW in hopes that you'd visit it quickly, I added a red link to the following page:

Talk:Degrees of freedom (physics and chemistry) ThorinMuglindir 14:27, 31 October 2005 (UTC)
I wasn't even aware that it was your edit, and deleted the red link, because it didn't add anything to that list. And I didn't look at the time, so I also didn't get that the page would be created soon. In any case, I'm not stalking you. Sorry. My bad. Karol 15:01, 31 October 2005 (UTC)
OK no problem. Your edits you do appear sound to me btw. We'd better get across as clearly as possible that diffusion is a very general phenomenon.ThorinMuglindir 16:21, 31 October 2005 (UTC)

[edit] Diffusion (mathematics)

I find this page only gives the physical view. There is also the mathematical term of a diffusion (process). Of course these concepts are related, but it's not the same. LARS 18:58, 19 November 2005 (UTC)

The mathematical term--and the other uses of diffusion--are in analogy to the mathematical models for the physical process, no? You can discuss the diffusion equation or a random walk without reference to the physical process, but then there are already articles on those topics. I added a statement about the analogies in the intro. Danrs 18:53, 15 August 2007 (UTC)

[edit] Giant animation

Somebody might want to remove the giant animated GIF from this page. Just sayin'.

  • What's your screen resolution? You might want to increase it... — 0918BRIAN • 2006-04-3 07:37
    • It's distracting and irritating, and the size contributes to this. My screen resolution is higher than average, yet I still find the image too big; I have a higher resolution because I want a greater density of information. It really doesn't take a 12x12 square of pixels to represent a particle. The image should be reduced to half size, and possibly slowed down (most of the animation shows random motion - the reader currently needs to watch the loop several times to catch the three seconds or so of diffusion). --Will 152.78.191.84 12:16, 14 June 2006 (UTC)

[edit] Why does diffusion happen faster in warmer systems?

Isn't it because warmer systems have more energy and higher energy molecules move fast? too bad i don't have a reference for that Tsinoyboi 16:16, 21 September 2006 (UTC)

[edit] Examples of diffusion

The example of the sugar cube in WATER is wrong, unless we could guarantee that water is completely still. Otherwise there will be some transport due to convection, and it is also likely that the "sugar water" neat the sugar cube will sink to the bottom of the glass due to its higher density and the gravitational force.—The preceding unsigned comment was added by 201.231.152.118 (talk • contribs) .

I have removed the examples listed as not being examples of diffusion, because the statement implies that they do not really contribute to the article. Perhaps they could be reworded so they can be included in the article. For instance, I would still think diffusion plays an important role (in addition to convection). Perheps this could be reworded to reflect the role of diffusion?--GregRM 21:57, 19 July 2006 (UTC)

Could it be convection and diffusion? i'm finding in my chemistry textbook that convection in an isolated system such as a closed flask are examples. Maybe the difference is that it be closed and a room has too much outside energy such as people or light. Tsinoyboi 17:14, 21 September 2006 (UTC)

[edit] Removed section

The following are NOT examples of diffusion:

  • A gas distributes itself over a room by diffusion
  • A sugar cube in a glass of water that is not stirred will dissolve slowly and the sugar molecules will distribute over the water by diffusion
  • Ink in a beaker of water is an example of diffusion. In the end, the ink particles spread evenly throughout the mass of water

According to my textbook, Chemistry & Chemical Reactivity, 6th edition, Thomson Brooks/Cole ISBN 0-495-01013-8, cover seen here http://www.newtexts.com/newtexts/book.cfm?book_id=3038, those count as diffusion that ultimately they become scattered. It says so on page It's supposed to be closed containers so they can be closed systems, it's just that those systems are open to other sources of energy to affect the rate system. Rate doesn't mean it's not diffusion. Warmer molecules will just mix faster. Being open systems, heat may be introduced like windows or people in a room, or escape like water evaporating from a beaker. The listed items are still molecules diffusion.

[edit] Diffusion and Thermodynamics

Diffusion and Thermodynamics are definitely related but can you say that diffusion occurs as a result of the second law of thermodynamics? isn't it more that The second law of thermodynamics works because of diffusion of heat? Tsinoyboi 16:15, 21 September 2006 (UTC)

Also, i found on Thermodynamic equilibrium #Equilibrium overview, "diffusive equilibrium" is used but there's no page for it. Tsinoyboi 16:34, 21 September 2006 (UTC)

hmm, i guess in Chemical potential, it states that entropy remains unchanged at equilibrium, but then again how is chemical potential related to diffusion? I still stand by diffusion as a result of the second law is incorrect. Tsinoyboi 16:34, 21 September 2006 (UTC)

I changed the third paragraph of nature of diffusion. I even cited my source --Tsinoyboi 07:28, 29 September 2006 (UTC)

Chemical potential gradients are what cause diffusion. This is why diffusion of, for example, matter, does not have to occur 'down a concentration gradient' - it will go in any direction which reduces the chemical potential. If this weren't true, we couldn't get spinodal decomposition. Mike 17:07, 17 May 2007 (UTC)

[edit] Example Animation is Convection not Diffusion

The example animation on the page shows a clear example of convection and bulk flow; the higher-density dye sinks in the glass of liquid (with turbulent fluid flow); barely any of the visible mixing is due to diffusion. After all, diffusion constants for small molecules tend to be a few hundred microns squared per second, meaning that it would take millions of seconds (weeks) for diffusion to equilibrate the dye concentration in the glass.

Does anyone want to keep that graphic as an example of "mixing that isn't diffusion"? Otherwise, even though it looks cool, I'll just delete it. Ichoran 04:29, 15 October 2006 (UTC)


You are right. http://en.wikipedia.org/wiki/Image:Diffusion.gif must be deleted from the diffusion or edited. -V.I. 17 November 2006

WHY?????? goddammit, quit deleting my edit...Will987654321 06:08, 1 December 2006 (UTC)will987654321

Because it is NOT diffusion -V.I.

I agree that the illustration is NOT an example of diffusion in the Fickian sense that this article is referring to. It is an example of convection. The time it would take to see Fickian diffusion at that scale is BIG. I think that the animation is very misleading and should be removed. When I get some time I will make a simulation of Fickian diffusion. -ZBS

I agree with the point that convection is not diffusion and doesn't belong here. A quibble about the use of "Fickian": usually it's used to contrast with other (non-Fickian) forms of diffusion, for example in complex systems, or where the flux depends on the magnitude of the concentration (in addition to the concentration gradient). It's a little odd to use Fickian to contrast with convection, which is not diffusion at all. Also, see Fick's law section below. Danrs 19:04, 15 August 2007 (UTC)

[edit] Fick's law

The introduction implied that Fick's law and Fourier's law were alternate names of the diffusion equation. Fick's law is used to derive the diffusion equation, but is not identical to it. Also, I think the important aspect of Fick's law is not that it labels the diffusing substance as mass (as opposed heat), which was implied, but that the net transport is proportional to the concentration gradient. There are other possibilities for purely diffusive systems! I tried to clarify this in the introduction. Danrs 20:04, 15 August 2007 (UTC)

[edit] Spontaneous Process

See my comment in the Spontaneous Process talk page.

[edit] A section for the shmucks

Is it possible for us to add a section into the article where this process is explained simply? I'm staring at the screen and cringing when I read this - maybe I just have unnaturally low intelligence. The Last Melon 01:53, 26 June 2007 (UTC)


I've tried to make the introductory paragraph more accessible to non-experts. Ichoran 19:03, 17 July 2007 (UTC)

Unfortunately, the introductory paragraph was edited to say that diffusion *is* the movement of particles, rather than that this is an *example*. I'm restoring the more general (i.e. more accurate) text. If there is a compelling reason to do otherwise, please mention the reasoning here! 128.177.16.8 19:10, 3 October 2007 (UTC)

[edit] Concentration gradient

"A concentration gradient is the difference between the high concentration and the low concentration. It also determines how fast diffusion occurs."

Isn't it more like the concentration gradient is a measure of how fast the diffusion is? // habj 21:17, 3 August 2007 (UTC)

No. The diffusion coefficient is the measure of how fast the diffusion is. The concentration gradient is the result of the initial condition, which diffusion tends to erase.
Both sentences from the quoted text have problems. The gradient is the difference between the high and low concentration _divided by the distance_. Also, it's the flux through a surface that is affected by the concentration gradient, not diffusion. Simple diffusion occurs independent of concentration and can be measured even in a uniform concentration field. For instance, the motions of particles in a well-mixed solution can be measured (e.g. using a microscope), and assuming pure diffusion their mean squared displacement will increase linearly in time (a dynamical hallmark of diffusion), with the constant of proportionality giving the diffusion coefficient, as described in the "Diffusion displacement" section. Danrs 22:16, 13 August 2007 (UTC)

[edit] Thermal diffusion ≠ Heat flow

Thermal diffusion ≠ Heat flow. Currently Thermal diffusion redirects here, and then this article sends it off to "Heat flow", which redirects to Heat transfer). This is not the best understanding of Thermal diffusion as in the OED or most places. — DIV (128.250.204.118 06:03, 21 September 2007 (UTC))

WHY CANT YOU ANSWER ANY OF MY QUESTIONS? —Preceding unsigned comment added by 88.107.212.41 (talk) 17:43, 2 October 2007 (UTC)

[edit] Diffusion experiments

The diffusion experiment with ammonia and cotton wool seems a little suspect to me. Won't the rapid evaporation of ammonia increase the local pressure and thus cause slight bulk flow within the tube? Wouldn't stabbing gelatin with a needle with ink be a better experiment? The key to doing a good experiment that demonstrates diffusion is to choose a system where non-diffusive flow is greatly retarded by viscosity or somesuch. Ichoran 19:55, 3 October 2007 (UTC)

[edit] WikiProject class rating

This article was automatically assessed because at least one WikiProject had rated the article as start, and the rating on other projects was brought up to start class. BetacommandBot 09:48, 10 November 200

this isn't reliable!!!!!!!!!!!!!!1

[edit] This etymology is complete bullshit.

The term diffusion is derived from the Latin verb husionere which means "to break" but can also mean "leave way"

There is no such word "husionere" in Latin. In fact, I can only assume this is vandalism, since it doesn't bear even a passing resemblance to reality.

http://www.m-w.com/

diffuse

Etymology: Middle English, from Latin diffusus, past participle of diffundere to spread out, from dis- + fundere to pour

dis-

Etymology: Middle English dis-, des-, from Anglo-French & Latin; Anglo-French des-, dis-, from Latin dis-, literally, apart;

http://archives.nd.edu/latgramm.htm

diffusilis -e [capable of spreading , elastic]

fusus (1) -a -um partic. from fundo; q.v.

fundo (1) fundere fudi fusum: of liquids [to pour , pour out]; of metals, [to melt, cast]. Transf., [to pour out, shower, give abundantly]; [to squander]; 'se fundere', [to rush, stream]; of sounds, [to utter]; with emphasis on distribution, [to spread, extend, scatter]; milit., [to rout, defeat, scatter, put to flight]. Hence partic. fusus -a -um, [spread out, extended]; 'crines', [flowing free]; of speech, [diffuse]; adv. fuse, [widely, copiously].

Proving once again that an encyclopedia predicated on popular consensus... sucks.

--75.63.48.18 (talk) 08:02, 8 January 2008 (UTC)