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Bang But No Splash

Hemos posted about 9 years ago | from the scientific-progress-goes-spash dept.

Science 252

BishopBerkeley writes "When a drop of ethanol is dropped on a surface at low pressures (1/5 atmosphere or less), it makes no splash. Science offers a brief synopsis and fascinating pictures of the phenomenon. The results seem to confirm the (perhaps counterintuitive) prediction that more viscous liquids are more likely to splash, not less likely . Links to the researchers' home page at U of Chicago (as of now, the site is timing out) and pdf version of the article on arxiv can be found on the Science page also."

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first moon (-1, Offtopic)

Anonymous Coward | about 9 years ago | (#12044985)


Slashdotted Already? (-1, Offtopic)

JuMpInG (728407) | about 9 years ago | (#12044993)

Finally, conclusive evidence that time travel is possible!

Re:Slashdotted Already? (-1)

Anonymous Coward | about 9 years ago | (#12045085)

It was down even before the article appeared here!

Synopsis: (3, Informative)

martensitic (747168) | about 9 years ago | (#12044994)

I do not have access to this item.

Fascinating. ----- Ut Tensio, Sic Vis

Re:Synopsis: (5, Informative)

Neophytus (642863) | about 9 years ago | (#12045001)

The PDF has the pictures [nyud.net]. I wish people wouldn't link redundant urls.

Re:Synopsis: (0)

Anonymous Coward | about 9 years ago | (#12045304)

Maybe it's my small monitor, but the graphs appear to be plotted with little wingdings of Robot Ducks equipped with propellers attached to shafts sticking out of their heads.

Re:Synopsis: (1)

pdbaby (609052) | about 9 years ago | (#12045470)

Yes, heaven forbid you were given a choice of how to access the content!
As we know from the computing industry, redundancy has absolutely no benefits...

The splash-dot has been slash-dotted (-1)

Anonymous Coward | about 9 years ago | (#12045277)


Nice! (3, Informative)

Anonymous Coward | about 9 years ago | (#12044995)

Your Free Registration does not grant access to this item:
Full Text : Cho,Sucking Away the Splatter, ScienceNOW 2005: 4

ScienceNOW text (5, Informative)

Anonymous Coward | about 9 years ago | (#12045069)

Sucking Away the Splatter

LOS ANGELES--Nature may abhor a vacuum, but a vacuum abhors a mess. In the absence of air, a droplet of liquid can crash into a smooth surface without splattering, physicists report. The odd phenomenon might be useful for controlling droplet formation in technological processes like inkjet printing.

Splashdown. A drop of ethanol hits a smooth glass at atmospheric pressure (above) and 1/5 atmospheric pressure (below).
CREDIT: Lei Xu et al./The University of Chicago

It seems obvious and inevitable that a fast-moving droplet will splatter when it hits a hard surface. Researchers have studied the distribution of droplet sizes and energies in such splashes, and physicists Lei Xu, Sidney Nagel, and colleagues at the University of Chicago were searching for ways to control those sizes and energies when they discovered something unexpected: By pumping away some of the surrounding air they could eliminate the splatter entirely.
Within a tall vacuum chamber, the researchers released droplets of alcohol onto a dry glass plate from heights ranging from 20 centimeters to 3 meters. They recorded the resulting splashes with a high speed video camera as they varied the pressure in their apparatus, sucking it down as low as one hundredth of atmospheric pressure. The droplets struck the surface with speeds ranging from 2 to 7 meters per second, and for a given speed, the researchers found they could eliminate the splash by lowering the pressure beyond a specific threshold.

The team explains the results with a simple theory. As a drop strikes a surface, liquid begins to spread sideways at supersonic speed, creating a shockwave. The shockwave pushes back on the liquid, and if that force is greater than the internal forces holding the drop together, the shockwave will lift the liquid off the surface and create a splash. Reducing the pressure reduces the force exerted by the shock wave.

Ironically, the theory predicts that a thicker liquid should splash more than a thinner one. The researchers tested this curious prediction by studying the splash made by three types of alcohol with different viscosities. Indeed, the more viscous the alcohol, the lower the pressure needed to prevent splashing, the team reported here this week at a meeting of the American Physical Society.

"It's not uncommon to see a lovely phenomenon, but it is uncommon to get all the factors straight," says Walter Goldburg, an experimenter at the University of Pittsburgh in Pennsylvania. Bulbul Chakraborty, a theoretical physicist at Brandeis University in Waltham, Massachusetts, says the researchers' analysis opens the way to controlling splashing in, for example, spray coating surfaces with various substances.

Re:Nice! (2, Insightful)

Anonymous Coward | about 9 years ago | (#12045111)

I guess the conversation was something like:

<sciencemag> Hi, we'd like to increase our readsership, in the following demographic: nerds
<osdn> Okay, we can give you the following options:
<osdn> "Sponsored Link", that'll cost you 100$
<osdn> "Flash ad", in science section, at 1000$
<osdb> "Flash ad", front page article, 2000$
<osdn> "Article in Science Section", it 5000$
<osdn> or, our most wanted product:
<osdn> "Article, Front page". 10000 $. Really really a lot of value.
<sciencemag> Can the article be a simple subscription link ?
<osdn> You pay, you do whatever you like
<sciencemag> What's the catch ?
<osdn> Well, we can't guarantee when we'll post it, as we're currently running a big Google campain. But it should be possible in a couple of days.
<sciencemag> Okay, we'll take that front page thing. Bye.
<osdn> Thanks. At your service.

Re:Nice! (3, Insightful)

MrP- (45616) | about 9 years ago | (#12045185)

this is the second article in 2 days posted on /. that requires payment.. yesterday there was an article that required you to be an AOL member to read it

wtf is going on??

Re:Nice! (5, Funny)

Eccles (932) | about 9 years ago | (#12045445)

Your Free Registration does not grant access to this item:
Full Text : Cho,Sucking Away the Splatter,

With a title like that, you would think it's "adult" content they're charging for...

Ethanol (5, Funny)

KiloByte (825081) | about 9 years ago | (#12044997)

Uh oh. Someone left some ethanol next to bored scientists again.

People like my friends know the right thing to do, but it appears that this knowledge is not common enough.

heh (0)

Anonymous Coward | about 9 years ago | (#12045114)

reminds me of a chemistry department in a university. They do some testing on beer samples, but only require a few drops .. now what happens to the rest of the beer in the can or bottle?

Re:heh (0)

Anonymous Coward | about 9 years ago | (#12045208)

Lemme guess - Do they throw it away?

From the article (1)

Lucky Kevin (305138) | about 9 years ago | (#12045258)

"These photographs were taken with a digital camera that can snap 47,000 images per second."

A bit faster than my Canon 10D! I want one!

Re:From the article (0)

Anonymous Coward | about 9 years ago | (#12045335)

Ahh, but the 10D is a fine camera nevertheless!

More beer research ... (3, Informative)

mikael (484) | about 9 years ago | (#12045496)

You might also want to read the following papers:

A Comparison Analysis of the Greater Carbohydrate and Increased Photosynthetic Element Count of Budweiser Versus the Similar Enzyme Content of Bud Light [msu.edu]

Next to medicine and biowarfare, brewing and fermentation technology [byo.com] is a major funding source for microbiology.

Some research suggests that drinking beer may stop your hair from turning grey [japancorp.net]

And possibly the most expensive PDF's in the world [just-drinks.com]

Hmm (4, Funny)

iLEZ (594245) | about 9 years ago | (#12045003)

" Your Subscription does not grant access to this item: Full Text : Cho,Sucking Away the Splatter, ScienceNOW 2005: 4"

Sounds like a whole different kind of webpage..

But does this apply to methanol? (-1, Offtopic)

vidarlo (134906) | about 9 years ago | (#12045004)

Otherwise, we finally have the solution we have awaited! Only to look for difference when dropping a drop of alcohol in your low-pressure chamber you always carry at parties... Oh wait, we where not supposed to drink t...

Bang AND splash (4, Funny)

Anonymous Coward | about 9 years ago | (#12045011)

When a few drops of ethyl alcohol are dropped into a low-tolerance system, you get bangs, splashes, crashes, all kinds of stuff.

More study is clearly needed.

An accessible page, more types of fluids tested (5, Informative)

ylikone (589264) | about 9 years ago | (#12045019)

Click here [uchicago.edu] to see.

Re:An accessible page, more types of fluids tested (5, Informative)

andy753421 (850820) | about 9 years ago | (#12045141)

For everyone without real player just change the *.splash.rm to *.splash.avi [uchicago.edu] on the video link since even the 'AVI format' link points to a real media file.
The movie seems to me much more effective than the jpg image, I was supprised by them skipping head so far between the 3rd and 4th frame, seems leaves out some of the important parts..

Re:An accessible page, more types of fluids tested (4, Informative)

shockbeton (669384) | about 9 years ago | (#12045167)

The link to the AVI is erroneous on the parent's linked-to page. It should be:

http://www-news.uchicago.edu/releases/05/050322.sp lash.avi [uchicago.edu]

A marvelous movie!

Re:An accessible page, more types of fluids tested (3, Insightful)

FatBear (835919) | about 9 years ago | (#12045478)

Yes it is a good movie. I see that the drop in the top frame is flattened, presumeably due to the resistance of the thicker air it is passing through. The drop in the lower frame/lower atmospheric pressure is more nearly a perfect sphere. Maybe that accounts for the splash/no splash effect? Kind of like the difference between a belly flop (flattened sphere) and a clean dive.

bah, registration required (-1, Offtopic)

Anonymous Coward | about 9 years ago | (#12045022)

nuff said

We know quarks, but not this... (5, Insightful)

Psychic Burrito (611532) | about 9 years ago | (#12045028)

Isn't it amazing that we're investigating quarks but haven't yet fully understood the properties of athmosphere and vacuum? We could have found those phenomena 400 years ago, but no...

Makes one wonder what else the laws of physics are hiding from us yet... and whether we have really tried to analyse physics systematically enough.

Re:We know quarks, but not this... (5, Interesting)

hey! (33014) | about 9 years ago | (#12045092)

Well, to be fair to the upper crust Elizabethan gentleman scientists of yore, photography wouldn't be invented for another two hundred years, and high speed emulsions for some decades after that. Now those 20th century scientists -- thats a different kettle of fish.

Re:We know quarks, but not this... (4, Insightful)

efatapo (567889) | about 9 years ago | (#12045093)

This doesn't seem that counter-intuitive though...High viscosity liquids have a greater molecular attraction to one another than low viscosity liquids. They would therefore show a resistance to spreading out on the glass. This would give them more solid-like properties and therefore would be more like a ball hitting a wall, where energy is transfered in a rebound. The lower viscosity liquids would not be held tightly together and would therefore spread out easier.

To test this it seems like you could perform the experiment at higher temperatures. The hypothesis would be that the higher temps overcome the molecular interactions and decrease the viscosity.

I just looked at the pictures and am a biochemist so take this analysis, like everything else on /., with a grain of salt. But this seems to make sense to me.

Daniel Coughlin's Photographs [pbase.com]

Re:We know quarks, but not this... (0)

Anonymous Coward | about 9 years ago | (#12045543)

Well, that's the thing. It didn't seem "counter-intuitive" to me either. Who decides what the heck is "intuitive" anyway? e.g. I was hopelessly confused for years by people telling me the X11 Server/Client thing was intuitively the "wrong way round". NO IT FREAKING ISN'T, DAMNIT! You're all MENTAL!

Re:We know quarks, but not this... (5, Insightful)

Hognoxious (631665) | about 9 years ago | (#12045107)

Isn't it amazing that we're investigating quarks but haven't yet fully understood the properties of athmosphere and vacuum? We could have found those phenomena 400 years ago, but no...
I'm not sure this is new. A housemate (who worked in a dairy) told me many years ago that milk is transported in vaccuum tankers to avoid it arriving as butter.

Re:We know quarks, but not this... (1)

madprof (4723) | about 9 years ago | (#12045142)

Scientific investigation takes places in many areas at once. It should come as no surprise that we have people investigating quantum phenomena while others are still exploring the properties of physical behaviour on a larger scale.

Re:We know quarks, but not this... (1)

Rostin (691447) | about 9 years ago | (#12045150)

In a sense, it is amazing. It seems like behaviors like these should be "easy" because we've had the tools to investigate macroscopic properties of fluids for a really long time.

But think of it this way. Your task is to understand the physics of one ping-pong ball verses the physics of many interacting ping-pong balls. Which do you think will be simpler?

As Dave Barry pointed out.... (5, Insightful)

MemeRot (80975) | about 9 years ago | (#12045222)

We invented nuclear bombs before we invented intermittent wipers for cars. Progress is never a smooth line.

Re:As Dave Barry pointed out.... (5, Funny)

That's Unpossible! (722232) | about 9 years ago | (#12045507)

Yes, but they only decided to proceed on the nuclear bombs when they realized dropping intermittent wipers on the Japanese would not end the war.

Re:As Dave Barry pointed out.... (-1, Offtopic)

aminorex (141494) | about 9 years ago | (#12045919)

A nuclear bomb can be detonated by taking two lumps of metal and banging them together real fast. The romans could have done that, easily.

In the Deccan plain of India, we
find cities made of sun-dried bricks that are glassified on one side, and significantly radioactive.

I don't know if Gurkha in his vimana used intermittent wipers, but he seems to have witnessed
something similar to a nuclear device in its
energy release, as we read in the Mahabharata: ...a single projectile
Charged with all the power of the Universe.
An incandescent column of smoke and flame
As bright as the thousand suns
Rose in all its splendour... ..it was an unknown weapon,
An iron thunderbolt,
A gigantic messenger of death,
Which reduced to ashes
The entire race of the Vrishnis and the Andhakas. ..The corpses were so burned
As to be unrecognisable.
The hair and nails fell out;
Pottery broke without apparent cause,
And the birds turned white.

After a few hours
All foodstuffs were infected... ...to escape from this fire
The soldiers threw themselves in streams
To wash themselves and their equipment...

Re:We know quarks, but not this... (1)

MtViewGuy (197597) | about 9 years ago | (#12045350)

I'm not surprised they found these results. After all, fluids of all types tends to behave really differently if you drastically change it from 980 millibars, the standard sea level air pressure. It has all kinds of applications from studying how explosives work to designing high-pressure hydraulic systems for airplanes.

Re:We know quarks, but not this... (0)

Scott7477 (785439) | about 9 years ago | (#12045750)

There are plenty of things that have yet to be understood by science: sonoluminescence, electron tunneling, chaotic fluid flow...the list goes on.
There was a book that came out a few years ago titled "The End of Science" which proposed that there was basically nothing new to discover. This was actually the mindset that prevailed at the end of the 19th century, right before the discovery of quantum physics. Kind of makes you wonder....

Yes, this is incredibly basic stuff. (1)

CarpetShark (865376) | about 9 years ago | (#12045870)

I'm not a physicist, but even I can (seemingly) work this stuff out from first principles: a rubber ball bounces more than a brick because it's a soft body that can be bent, distorted, and recoiled by the forces involved in hitting the ground. Likewise, a more viscous liquid can hold in its forces more than a "lesser" liquid, and its shape will bend and distort as the forces (and fluid) push around inside it. Nothing counter-intuitive there to me.

Now, knowing something intuitively and validating it scientifically are two different things, and I (at least) wasn't aware that some liquids don't bounce, so I welcome this research of course. But I hope it leads to something a little more groundbreaking than that ;)

I'd also like to know if this ethanol is REALLY not bouncing all of a sudden, or if it's just bouncing less so that it becomes undetectable.

Re:We know quarks, but not this... (5, Interesting)

nameer (706715) | about 9 years ago | (#12046040)

This one has me stumped:

A small balloon is inflated in atmospheric pressure until it pops. The resulting fragments are a few large pieces of latex.

A simmilar balloon is inflated by tying it off, placing it in a bell jar, and evacuating the jar. When the balloon pops, the result is a shredded mess of many small pieces of latex.

The guy at the museum who showed this demonstration couldn't explain to me why it did this. He just kept saying, "It pops everywhere at once". Okay, but why?

since the article is already /. (2, Funny)

leuk_he (194174) | about 9 years ago | (#12045043)

(1 seems to be subscription only, other is alredy /.?)

Lets continue doing those experiments with alcohol ourself. In a plane. Mixed with lots of water (beer) , mixed with less water (jenever). Ans splashing.

Anything more useful to report about alcohol abuse?

Just in case you have no access to the pdf either (1)

kabbor (856635) | about 9 years ago | (#12045047)

1 Drop splashing on a dry smooth surface Lei Xu, Wendy W. Zhang, Sidney R. Nagel* The James Franck Institute and Department of Physics, The University of Chicago, 5640 South Ellis Avenue, Chicago, Illinois 60637, USA. *To whom correspondence should be addressed. Email: srnagel@uchicago.edu The corona splash due to the impact of a liquid drop on a smooth dry substrate is investigated with high speed photography. A striking phenomenon is observed: splashing can be completely suppressed by decreasing the pressure of the surrounding gas. The threshold pressure where a splash first occurs is measured as a function of the impact velocity and found to scale with the molecular weight of the gas and the viscosity of the liquid. Both experimental scaling relations support a model in which compressible effects in the gas are responsible for splashing in liquid solid impacts. 2 What is the mechanism for the violent shattering that takes place as a liquid drop hits a smooth dry surface and splashes? How does the energy, originally distributed uniformly as kinetic energy throughout the drop, become partitioned into small regions as the liquid disintegrates into thousands of disconnected pieces? It is not surprising that the velocity of impact, the drop size and shape, or the liquid surface tension has an important effect on the mass and energy distribution of the ejected droplets [1, 2]. However, it is perhaps more difficult to imagine that the surrounding air has a significant role to play in this all-too-common occurrence. More to the point, one would hardly expect the splash to disappear if the surrounding atmosphere were removed. Nevertheless this is the case. The elegant shapes formed during a splash have captured the attention of many photographers since the remarkable early images of Worthington showing the shapes that occur as milk or mercury hits a smooth substrate [3]. Many studies have focused on the fingering dynamics [4 7] and the effect of surface roughness [1, 2, 8]. In the present study, we focus only on a drop hitting a smooth substrate. The top row of Figure 1 shows four frames from a movie of an alcohol drop hitting a dry glass slide in a background of air at atmospheric pressure. The drop, after impact, spreads and creates a corona with a thickened rim which first develops undulations along the rim and then breaks up due to surface tension. During this process, the thin sheet comprising the corona surface retracts and rips into pieces. These images are reminiscent of the corona caused by a drop hitting a thin layer of fluid photographed by Edgerton and his colleagues [9]. However, in our case we have made sure that the slide is completely dry prior to impact. Our images illustrate an important puzzle: why do we see a corona form at all? At the substrate surface the liquid 3 momentum points horizontally outward. Without a layer of fluid to push against (such as in the photographs of Edgerton), how does the expanding layer gain any momentum component in the vertical direction? Fig. 1. Photographs of a liquid drop hitting a smooth dry substrate. A 3.4 ± 0.1 mm diameter alcohol drop hits a smooth glass substrate at impact velocity V0 = 3.74 ± 0.02 m/s in the presence of different background pressures of air. Each row shows the drop at four times. The first frame shows the drop just as it is about to hit the substrate. The next three frames in each row show the evolution of the drop at 0.276 ms, at 0.552 ms and at 2.484 ms after impact. In the top row, with the air at 100 kPa (atmospheric pressure), the drop splashes. In the second row, with the air just slightly above the threshold pressure, PT = 38.4 kPa, the drop emits only a few droplets. In the third row, at a pressure of 30.0 kPa, no droplets are emitted and no splashing occurs. However, there is an undulation in the thickness of the rim. In the fourth row, taken at 17.2 kPa, there is no splashing and no apparent undulation in the rim of the drop. 4 Our experiment is straightforward: Reproducible drops of diameter D = 3.4±0.1 mm were released from rest at different heights above a glass microscope slide laid horizontally inside a transparent vacuum chamber. The pressure, P, could be varied between 1 kPa and 100 kPa (atmospheric pressure) and the height of the nozzle above the substrate could be varied between 0.2 m and 3.0 m. The subsequent splash was recorded by a Phantom V7 high-speed video camera at a frame rate of 47,000 fps. The impact speed of the drop was also determined from these movies. Because the drop shape oscillates after it leaves the nozzle, we adjusted the height carefully so that, in all the measurements reported below, the profile of the drop was nearly circular at the instant that it made contact with the slide. Also, in order to avoid contamination of the glass due to the possible residue left by previous drops, we replaced the substrate with a fresh slide after every measurement. We have used three different liquids (methanol, ethanol and 2-propanol) for the drop and four different gases (helium, air, krypton and SF6) for the surrounding atmosphere. The liquids that we chose all wet the substrate so that there is no subsequent retraction and rebound of the drop [10]. The rows of Fig. 1 show images of the splash at different background air pressures for a drop of ethanol hitting the substrate at a velocity V0 = 3.74 ± 0.02 m/s. Surprisingly, as the pressure is lowered, fewer droplets are ejected from the surface; below P = 30 kPa no droplets emerge at all after impact. We are able to determine the threshold pressure at which splashing occurs, PT [11], as a function of impact velocity, V0. In Fig. 2a, we show PT versus V0. As expected over most of the range, PT decreases as the impact velocity is raised. However, there is one region below V*, where this is not true and the curve is nonmonotonic. In this low velocity regime, splashing is doubly re-entrant. As we will show, this effect appears with other liquids and other gases. 5 Fig. 2. Threshold pressure versus impact velocity. (a), PT is plotted versus V0 in a background atmosphere of air. The data is non-monotonic in the region V0 V*, for the four gases shown in the inset. 6 Clearly the pressure of the gas is essential for determining whether or not the drop will splash. However it is not obvious what physical property of the gas is important. We note that the dynamic viscosity of the air does not vary with pressure until the mean free path of the molecules is the size of the geometric length scales of the system. We are well above that regime in these experiments. We also measured [12] that the surface tension of the liquid does not vary with pressure in our experimental regime. In order to understand its role better, we have varied the composition of the gas. The inset to Fig. 2b shows the threshold pressure versus impact velocity for four different gases; the values of PT are displaced from each other but the trends in the data have the same qualitative shape. We note that the four gases used have similar viscosities (varying only from 15.3 Pa s for SF6 to 25.6 Pa s for Kr) [13] but have very different molecular weights, MG (MHe = 4, Mair = 29, MKr = 83.8, and MSF6 = 146 Daltons) [13]. We have tried to scale the different curves on top of one another and found that the best data collapse, in the region with impact velocities greater than V*, is obtained by plotting (MG/Mair) 0.5 PT versus V0. The result is shown in the main panel of Fig. 2b. Our analysis concentrates entirely on the regime with V0 > V*. We consider two contributions to the stress on the expanding liquid layer after impact: the first, £G, is due to the restraining pressure of the gas on the spreading liquid, which acts to destabilize the advancing front and deflect it upward; the second, £L, is due to the surface tension of the liquid, which favours keeping the liquid layer intact after impact. When the two stresses become comparable, we expect the spreading liquid to become unstable and to break up into droplets. On impact, the drop spreads out suddenly and rapidly. An estimate of £G should therefore include the effects of the shock wave that the liquid creates in the air. We apply 7 the water-hammer equation [8] to the gas phase [14] which states that the stress is proportional to the gas density, ÁG, the speed of sound in the gas, CG, and the expanding velocity of the liquid layer on the substrate, Ve: G G CG Ve PMG k BT k B T MG RV 0 2 t . (1) Here is the adiabatic constant of the gas, T is the temperature, kB is Boltzmann's constant, R is the initial radius of the drop and t is the time measured from the instant of impact. In order to estimate £L, we consider the surface tension pressure near the front of the advancing liquid. This is given by the surface tension coefficient, Ã, divided by the thickness of the layer, d. The thickness d is assumed to be the boundary layer thickness which is controlled by the diffusion of vorticity from the solid substrate [15]. Thus: L = / d / Lt (2) where ½L is the kinematic viscosity of the liquid. These estimates imply: G L M G P RV0 2k BT L (3) which is independent of time. When the two stresses are comparable, the expanding liquid rim is slowly destabilized and deflected upwards for an extended period of time, finally resulting in the ejection of droplets. This equation predicts another non-intuitive result: a more viscous liquid splashes more easily than a less viscous one. That is, the threshold pressure should decrease if the liquid viscosity is raised. To test this prediction, we have studied splashes from three different alcohols (methanol, ethanol and 2-propanol) that have essentially the same density and surface tension but different kinematic viscosity (½meth = 8 0.68, ½eth =1.36, and ½2-prop = 2.60 Pa s m3/kg) [13]. The results for PT versus V0 are shown in the inset to Fig. 3. Indeed, it is the case that 2-propanol, the liquid with the largest viscosity, has the lowest threshold pressure. The main panel of Fig. 3 shows PT (½L /½eth) 0.5 versus V0 for all the liquids studied in the regime V0 > V*. There is a good collapse of the data. In Fig. 4, we show the ratio: £G/£L at the threshold pressure for all our data with V0 > V*. The ratio is approximately constant, independent of impact velocity, with £G/£L ~ 0.45. This indicates that £G and £L are comparable at the threshold pressure, as we expected. Fig. 3. Effect of liquid viscosity. Inset shows PT versus V0 for three liquids: methanol ( ), ethanol ( ) and 2-propanol (+), in a background atmosphere of air. Main panel shows the scaled threshold pressure, PT (½L/½eth) 0.5, versus the impact velocity, V0, in the region V0 > V*, for the three liquids shown in the inset. We have shown that, surprisingly, the presence of a surrounding gas is essential for splashing to occur on a dry flat substrate. Moreover, it provides a means for creating the 9 corona with a vertical component of momentum which would be difficult to produce without gas being present. Several puzzles remain. Although we have made an estimate, which concurs with the experimental data, for where splashing should occur if the impact velocity is sufficiently large, we have no similar estimate for what should happen in the low-velocity regime. Indeed, we do not yet know why there is a separate regime at small V0. Likewise, we suspect that there may be other regimes, for example when the liquid viscosity becomes large or when the impact velocity becomes comparable to the sound speed in the gas. Fig. 4. Ratio at threshold of £G, the destabilizing stress due to the gas, to £L, the stabilizing stress due to surface tension. £G / £L is plotted versus V0, in the region V0 > V*, for all the liquids and gases studied. The discovery that the surrounding pressure and gas composition can influence the occurrence of splashes, should have important technological ramifications in the many situations where splashing is involved such as in combustion of liquid fuels [16], spray drying [17], ink-jet printing [18], and industrial washing. For example in the case of 10 surface coating, where splashing causes problems, we can either pull a vacuum or simply vary the composition of the gas to one with a low molecular weight. In other cases, where splashing is desired, we can do just the opposite. This provides a technique to control splashing precisely. We wish to thank Christophe Clanet, Itai Cohen, Haim Diamant, Christophe Josserand, Stephan Zaleski, and Ling-Nan Zou for helpful discussions. This work was supported by NSF 0352777 and NSF MRSEC DMR-0213745. References and Notes [1] C. Mundo, M. Sommerfeld, C. Tropea, Int. J. Multiphase Flow 21, 151 (1995). [2] C.D. Stow, M.G. Hadfield, Proc. R. Soc. Lond. A: Math. Phys. Sci. 373, 419 (1981). [3] A.M. Worthington, Proc. R. Soc. Lond. 25, 261 (1876-1877). [4] S.T. Thoroddsen, J. Sakakibara, Phys. Fluids 10, 1359 (1998). [5] R. Bhola, S. Chandra, J. Mater. Sci. 34, 4883 (1999). [6] M. Bussmann, S. Chandra, J. Mostaghimi, Phys. Fluids 12, 3121 (2000). [7] N. Z. Mehdizadeh, S. Chandra, J. Mostaghimi, J. Fluid Mech. 510, 353 (2004). [8] O.G. Engel, J. Res. Natl. Bur. Stand. 54, 281 (1955). [9] H. E. Edgerton, J. R. Killian, Jr., Flash! Seeing the Unseen by Ultra High-speed Photography (Boston C.T. Branford Co., Boston, 1954). [10] D. Richard, C. Clanet, D. Quéré, Nature 417, 811 (2002). [11] Oscillations in the drop after it leaves the nozzle can induce small variations in the measured value of PT of ±4 kPa depending on the drop shape as it hits the substrate. By focusing only on drops that have a circular profile on impact, we eliminate this effect. 11 [12] F. K. Hansen, G. Rodsrud, J. Colloid Interface Sci. 141, 1 (1991). [13] D. R. Lide, Ed., CRC Handbook of Chemistry and Physics (CRC, New York, 1996 1997). [14] It is worth noting that we are applying the "water hammer" equation to the gas phase while it is normally applied to the liquid phase. [15] C. Josserand, S. Zaleski, Phys. Fluids 15, 1650 (2003). [16] K. R. Koederitz, M. R. Evers, G. B. Wilkinson, J. A. Drallmeier, Int. J. Engine Research 3, 37 (2002). [17] F. V. Shaw, Ceramic Bulletin 69, 1484 (1990). [18] J. L. Zable, IBM J. Res. Develop. 21, 315 (1977).
(formatting and pictures lost. Sosume)

Bang But No Splash: (-1, Offtopic)

Anonymous Coward | about 9 years ago | (#12045054)

she makes you wear a condom.


you shoot yourself but there's no exit wound.

How would superfluids behave? (3, Interesting)

ram4 (636018) | about 9 years ago | (#12045058)

It would be interesting to investigate how superfluids behave.

Since the article hints that the more viscosity, the lower the pressure must be to avoid splashing of the droplet, would superfluids (which have no viscosity at all) behave as expected even under the atmospheric pressure, or even a higher pressure?

Offhand, why are they using ethanol and not water for their study though?

Re:How would superfluids behave? (1)

ram4 (636018) | about 9 years ago | (#12045072)

Following up on myself: they are using ethanol and not water because water is much harder to splash than ethanol.

I found the answer in another article dealing with the subject.

Re:How would superfluids behave? (5, Informative)

MustardMan (52102) | about 9 years ago | (#12045215)

To follow up on your follow-up, water is hard to splash because it's a polar molecule. There's a slight positive charge off to one side and a slight negative charge off to the other. Hence, the molecules of water tend to attract each other. They also attract lots of other stuff, which is why water is so great as a solvent, why you get a meniscus at the top of a test tube, why rain droplets form nice round bubbles on the surface of your car, etcetera.

Sometimes in science I tend to get caught up with the complex math and theory, and forget the basic stuff. Water is a truly fascinating material, and can give us a lot of insight into the workings of the world.

Re:How would superfluids behave? (1, Informative)

Anonymous Coward | about 9 years ago | (#12045994)

Ethanol is a polar molecule aswell, not as polar as water though.

Makes you wonder - (-1, Troll)

syrinje (781614) | about 9 years ago | (#12045059)

- who or what is a Cho and why is it/he/she sucking splatter? WTF is splatter an euphemism for now? What's that you say...? Ewwwwwwwwww......

slow day eh ... (-1, Troll)

Anonymous Coward | about 9 years ago | (#12045063)

why is this story worthy of /.? can anyone explain?

Sigh (-1, Troll)

edittard (805475) | about 9 years ago | (#12045077)

Science offers a brief synopsis and fascinating pictures of the phenomenon.
As they say in France, oppsite water. Or as they say in English, no it fucking well doesn't. Nice to see that when michael 'left', Hemos (with a silent exual) stepped up to the plate and batted like a true cretinous fucktard.

So... (-1, Troll)

TrappedByMyself (861094) | about 9 years ago | (#12045089)

is this one of those empowerment articles they occasionally post to make Slashdot readers feel all smart and stuff?

"Oh noes! People say that we're just a Linux hype machine!"
"Quick, do a Google search on 'science' and post the first thing you see!"

Ethanol cooled by Liquid Nitrogen (0)

Anonymous Coward | about 9 years ago | (#12045095)

Ethanol turns into a thick syrup when cooled sufficiently. LN2 works nicely. And, yes, I've tried it. Just don't try to drink it.

a very interesting question... (3, Insightful)

dAzED1 (33635) | about 9 years ago | (#12045128)

Our images illustrate an
important puzzle: why do we see a corona form at all? At the substrate surface the liquid momentum points horizontally outward. Without a layer of fluid to push against (such as in the photographs of Edgerton), how does the expanding layer gain any momentum component in the vertical direction?

That is an interesting question...sounds like a potential thesis for a few people out there.

Re:a very interesting question... (1)

Nasher (868384) | about 9 years ago | (#12045272)

It is interesting. Looking at the profile where the liquid first starts to seperate from the surface it reminded me of a boundary layer forming. Perhaps it's liked to that initially, a step change then as the shock forms and the air becomes incompressible causing the fluid to break in the horizontal and all motion to be vertical. But what then causes it to kink back out again at the top of the vertical travel? Some sort of pressure effect perhaps.

Re:a very interesting question... (2, Interesting)

rorrison (74822) | about 9 years ago | (#12045336)

Off the top of my head... as the liquid is moving horizontally along the surface, it encounters air molecules, which causes the leading edge of the surface to pile up. As it piles up, it acquires the vertical component. Less air pressure -> less air molecules encountered -> less piling up -> less vertical component -> less splashing.

Friction with the surface will slow down the liquid at the surface, but without the air resistance liquid not in contact with the surface just flows over the slower liquid at the surface and so doesn't pile up.

Of course, IANAP, so this worth exactly what you paid for it. If, on the other hand, I happen to be right -- remember, you heard it here first!

Re:a very interesting question... (-1)

Anonymous Coward | about 9 years ago | (#12045823)

I think you'd get that even in a hard vacuum, because the leading edge has to deal with the surface tension grabbing the surface. The edge of the puddle has to be pushed to overcome this, so it'll pile up somewhat.

LESS viscous liquids are more likely to splash (2, Informative)

Dikeman (620856) | about 9 years ago | (#12045157)

The posting says:
"The results seem to confirm the (perhaps counterintuitive) prediction that more viscous liquids are more likely to splash, not less likely"

While the article says:
"Xu tested water splash as well. Water exhibits the same behavior, but its higher surface tension narrows the range of splash-forming impact velocity and creates a much larger margin for experimental error.
"It's much harder to splash than ethanol," he said."

Is say, this is a classic RTFA

Re:LESS viscous liquids are more likely to splash (5, Informative)

Herbster (641217) | about 9 years ago | (#12045238)

uh. surface tension and viscosity are NOT the same thing.

Nope. (1)

anpe (217106) | about 9 years ago | (#12046020)

Have a look at the PDF:
This equation predicts another non-intuitive result: a more viscous liquid splashes more easily than a less viscous one.

Bad link (1)

The Cisco Kid (31490) | about 9 years ago | (#12045223)

The link given is to a login page, not to an article. It would be really nice if the editors caught these and filtered them out before posting.

Re:Bad link (3, Interesting)

Dachannien (617929) | about 9 years ago | (#12045874)

The OP is probably at an institution where they have a site subscription to Science (most American universities worth their salt do, for example), so when they go to the link they get the article right away. If Hemos is somewhere that has a site subscription to Science, he'd get the same thing, and it would be a relatively subtle thing to figure out whether nonsubscribers can read the article or not.

Is this the same everywhere? NO! (-1, Redundant)

LokieLizzy (858962) | about 9 years ago | (#12045251)

In Soviet Russia, the globs of ethanol drop YOU!

(I'm sorry, *someone* had to do it)

Camera - OT (1, Interesting)

FreeLinux (555387) | about 9 years ago | (#12045254)

The pictures were captured by the Phantom V7 camera at a rate of 47,000fps.

I wonder how long it will take to get a digital equivalent of this camera?

Re:Camera - OT (0)

Anonymous Coward | about 9 years ago | (#12045378)

that camera is digital.

Re:Camera - OT (5, Funny)

cluke (30394) | about 9 years ago | (#12045408)

Good job too. Imagine leaving that into the chemist to get developed. "Just the the one set of my 47,000 prints please". And then you get them all back with a 'photography tips' sticker on as you had your thumb over the lens.

Re:Camera - OT (-1)

Anonymous Coward | about 9 years ago | (#12045455)

i work with these cameras and they are pretty neat

Re:Camera - OT (-1)

Anonymous Coward | about 9 years ago | (#12045494)

Actually, it *is* a digital camera.

Does drop size matter? (0)

Anonymous Coward | about 9 years ago | (#12045273)

I tried a thought experiment. What would happen if I dropped a pail of marbles on the floor (this being like a liquid with zero surface tension). As each marble hits the floor it would like to bounce upward but it is constrained by the marbles above it. It would therefore tend to go horizontally. If I made the marbles sufficiently small and numerous, I suspect that I wouldn't see anything that looked like a splash. ie. the splash-like behaviour would be small in relation to the size of the 'drop'.

My question is this: If you made the liquid drops sufficiently small, would the behaviour change?

Re:Does drop size matter? (1)

hcob$ (766699) | about 9 years ago | (#12045323)

As any geek will tell you... size ALWAYS matters! Even if it's only related to the hardware you recently bought.

Re:Does drop size matter? (0)

Anonymous Coward | about 9 years ago | (#12045463)

10 years ago, as part of coursework for A-level phsyics we had to find something to investigate and write-up etc...
I decided to try to determine the factors behind splash height when dropping various masses and sizes of marbles into containers of water.
Got set up with borrowed video camera and was most amused to find that virtually every marble dropped from heights up to 1 meter or so caused no splashes what-so-ever...
Had to make up all the results in the end, just so I'd have something to report.

Air pressure is critical (5, Informative)

jbeaupre (752124) | about 9 years ago | (#12045325)

This was discussed in Science News (or maybe elsewhere) some time back so I'm working from memory. One of the things reseachers noted was that air was crucial for splashing. It's rather intuitive in a way. All of the momentum is downward, then converted to radially outward. What makes it go up? The leading edge of the droplet is rushing outward. With the right speed and gas pressure, it splashes up like popping the hood of your car while going down the highway. Get rid of the speed or the gas and it will stay low.

looking at the pix (3, Insightful)

GuyFawkes (729054) | about 9 years ago | (#12045361)

it looks like all the "splash" is created by the outward spread of the liquid from ground zero, it rushes outwards, but appears to "catch air" presumably because the surface tension / minimum stable raduis has been exceeded, and from that point on it becomes chaotic mixture of small droplets going every which way.

f=ma & you can't push a string (0)

Anonymous Coward | about 9 years ago | (#12045491)

"Researchers in the field previously had seen no reason for low atmospheric pressure to affect the results of their splash experiments."

researchers in the field must not know much about fluid dynamics and boundaries.

the liquid tries to displace the gas which is somewhat 'stuck' to the surface. lower pressure results in less mass to displace and less 'stickiness'. if the mess around with surface textures they'll see classical fluid dynamics variations. nano-scale aspects would make for interesting study.

elegant (5, Funny)

FLOOBYDUST (737287) | about 9 years ago | (#12045500)

Science at its best. Their explanation passes the three fingers rule. If a complicated subject can be distilled into a written answer that makes sense and can be covered with three fingers, that is elegance. However, don't be confused with answers that makes sense after ingesting three fingers of straight ethanol......

Simulations? (3, Interesting)

geordieboy (515166) | about 9 years ago | (#12045623)

What would be great is to check this phenomenon out with computer simulation. It might be tough to set up though, since you'd have to deal with a compressible gas phase and incompressible fluid phase, and keep track of the fluid surface to account for surface tension. I'm sure it could be done though. Axisymmetric simulation would probably be fine to start off.

Keyword: multiphase flows, fluid-fluid interaction (2, Informative)

xlurker (253257) | about 9 years ago | (#12046022)

What would be great is to check this phenomenon out with computer simulation.

That's exactly the first thing I thought of. And this begs to be simulated.

It might be tough to set up though, since you'd have to deal with a compressible gas phase and incompressible fluid phase, and keep track of the fluid surface to account for surface tension.

You pretty much described what is done. The Navier-Stokes equations for compresible and incompressible fluids are used. But in this case air-compression is so low, that incompressiblity could be assumed. All of the difficulty here is tracking the surface and maintaining surface tension. From the equations you can read that the surface tension will depend on two things: pressure jump and the jump of the normal derivative of the fluid velocity. Possibly an artificial surface tension could be added that depended on the change of curvature of the interface surface.

I'm sure it could be done though. Axisymmetric simulation would probably be fine to start off.

Only recently, the preferred approach to date uses a method called the level set method. Here the interface is explcitly tracked. Problems arise here because originally the numerical methods and underlying mathematics that are used weren't set up for changing domains i.e. changing differential equations in the middle of a discrete spacial cell in (a finite element).

I think this is the ink application they mentioned (2, Funny)

kb9vcr (127764) | about 9 years ago | (#12045702)

Note: This printer has been designed to work in a low atomosphere environment for optimal ink transfers. Reduce air pressure to 17.2 kPa before printing else warrenty will be VOID.

Bang But, No Splatter, Sucking Away the Splatter? (0)

Anonymous Coward | about 9 years ago | (#12045838)

I think the choice of words is a bit distracting...

Real world.. (3, Insightful)

Keamos (857162) | about 9 years ago | (#12046037)

Can someone explain to me what the significance of this in the real world is? I'm failing to see this (honestly, I'm not trying to be a troll)
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