Why Does Water Expand When it Cools? A New Explanation

Jul 17, 2009 By Miranda Marquit feature
water
Water Droplet. Image: Wikimedia Commons.

(PhysOrg.com) -- Most of us, when we take our first science classes, learn that when things cool down, they shrink. (When they heat up, we learn, they usually expand.) However, water seems to be the exception to the rule. Instead of shrinking as it cools, this common liquid actually expands. In order to explain this phenomenon, some scientists have adopted the “mixture” model, which purports that low-density, ice-like components dominate due to cooling. Masakazu Matsumoto, at the Nagoya University Research Center for Materials Science in Japan, has a different idea. He describes his findings in Physical Review Letters: "Why Does Water Expand When It Cools?"

“Theoreticians often describe that ice-like local structure emerges in the super-cooled liquid water by cooling, and increase of such heterogeneous low-density domain causes the density anomalies,” Matsumoto tells PhysOrg.com. “Such an explanation is easy to imagine and looks plausible. Experimentalists tend to believe the theoretician’s beautiful and simple model, and interpret their data based on this.”

However, such heterogeneity as must occur in this mixed model has not been truly proven experimentally. Matsumoto set out to model super-cooled water, and see if he could discover the mechanism behind the expansion of water under conditions that should make it shrink. In a previous work (M. Matsumoto, A. Baba, and I. Ohmine, J. Chem. Phys. 127, 134504 (2007)), Matsumoto offered a new method of analyzing the hydrogen bond found in super-cooled liquid water. “I found that the structure of supercooled water can be tessellated into a variety of polyhedron-like structure, vitrites,” he says. “I thought the issue would be a good chance to test my method.”

“Water is a network-forming matter. You can imagine the structure of the network as a kitchen sponge,” Matsumoto continues. “The sponge structure is originally a kind of foam but membranes are lost, and only the beams - bonds - remain. In both network of water and kitchen sponge, four bonds meet at a point, or node, to form a three dimensionally connected random network. As Plateau pointed out in 19th century, four beams of a foam crosses at a node with regular tetrahedral angle - Maraldi's angle - similar to the water’s hydrogen bond network.”

Matsumoto used computer simulation to look at three ways to change the volume of the foam cells: extension of the bonds, a change in the containing angle between the bonds, and a change in network topology. “By discriminating the three contributions, the mechanism became very clear. One contributes to thermal expansion, another one contributes to thermal contraction, and the last one does not. Density maximum is a result of these competing contributions,” he explains.

“I found that the thermal volume contraction is due to the deviation of bond angles from the regular tetrahedral angle,” Matsumoto says. He also applied his former idea of vitrites to classify local structures. “Any kind of local structure shrinks when bond angle is distorted from the regular tetrahedral angle. In other words, local structural variety is not the principal factor contributing to the thermal contraction. Water shrinks homogeneously by thermal angular distortion, regardless of local structural variety.”

Right now, though, reproducing the results of Matsumoto’s simulation experimentally is a rather difficult task. “It is still very difficult to observe microscopic heterogeneity by experiments.” He hopes, though, that his simulation will at least get theoreticians and experimentalists thinking about alternatives to idea of an ice-like, low-density domain growing in liquid water through cooling. “My finding will affect to the interpretation of experimental data on super-cooled water as well as water in the vicinity of walls, solutes, biomolecules.”

Moving forward, Matsumoto hopes to use computer simulation to tackle water polyamorphism. “There are several materials which invoke liquid-liquid coexistence. Most apparent case is observed in phosphor, and tetrahedral network materials such as water, silicon, silica and germanium, are supposed to be the case, too,” he insists. “By computer simulations, many people also have reproduced the liquid-liquid coexistence. However, nobody ever explained how and why two liquid phases of a single component can share the interface.”

It appears that water is much more interesting than many of us ever could have imagined.

More Information:

Masakazu Matsumoto, “Why Does Water Expand When It Cools?” (2009). Available online: http://link.aps.org/doi/10.1103/PhysRevLett.103.017801 .

M. Matsumoto, A. Baba, and I. Ohmine, “Network Motif of Water.” Journal of Chemical Physics (2007). Available online: theochem.chem.nagoya-u.ac.jp/w… rk+motif+of+water#p0 .

Copyright 2009 PhysOrg.com.
All rights reserved. This material may not be published, broadcast, rewritten or redistributed in whole or part without the express written permission of PhysOrg.com.

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User comments : 15

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robbor
1 / 5 (15) Jul 17, 2009
another question is why does the moon not rotate at all...not even a little bit.
RealScience
5 / 5 (14) Jul 17, 2009
That's not relevant to this article.

And the moon does rotate.
To a large extent it is tidally locked to the Earth, and hence rotates once a month to keep the same face towards the earth.
The locking is not perfect - even within that rotation the moon sways back and forth a little bit so that we see a bit more than half of the surface.
GPG
4.4 / 5 (5) Jul 18, 2009






The locking is not perfect - even within that rotation the moon sways back and forth a little bit so that we see a bit more than half of the surface.

Because it's orbit is elliptical.
JukriS
1 / 5 (14) Jul 18, 2009
This is because nucleus of atoms expand all a time. Nucleus of atoms explod all a time and emit/radiate waves of energy, that have a nature of electrons and particles. Also electrons and particles explod and amit/radiate waves of energy. Electrons just move to next eplod nucleus of atoms and get this expod faster and faster. Before that electrons just give some chabge of pressure for waves of energy who push themselfs out from explod nucleus of atoms and then born new electrons etc.....

Water molecul also control energy who coming other water molecul and water molecul can get this energy bending right there, where water molecul is. that happend easy way, when energy dont come so much from outside. When water is about 4 celsius, it working very well, you know!

http://onesimplep....com/296


.
JukriS
1 / 5 (12) Jul 18, 2009
When water is 2 celsius, outside is not coming so much energy and thats why watermolecul can control easy way waves of energy who come other water molecul with wavesof energy what water molecul emit/radiate. With this waves of energy water molecul get this waves of energy curving/bending right way there where water molecul is.

When water is 0 celsius and under, then expand/explod watermolecul logged to explod near by near.

Al that energy who go right to way next explod water molecul can push that water molecul strong way and thats why water expand faster that other stuff, when water get cooler!

When energy come more from outside and water get warm to 0 celsius to 4 celsius, then that outside energy, brake balance and that energy what watermolecul emit, cant go right away to next watermolecul and some go some other watermolecul who is behind next watermolecul.

Sapce dont expand or curv.

Nucleus of atoms is only energy that explod/expand all a time!

There is only one force and that force is PRESSURE. PUSH force.

changing of pressure and nothing else!
robbor
1 / 5 (5) Jul 19, 2009
get a ball and poke it with a 3 foot stick. hold the stick outward and rotate. the point at which the stick enters the ball always faces you. it does so because the ball is not rotating which is, in effect, the same as the moon. the moon does not rotate.
Alizee
Jul 19, 2009
This comment has been removed by a moderator.
QubitTamer
not rated yet Jul 20, 2009
When water is 2 celsius, outside is not coming so much energy and thats why watermolecul can control easy way waves of energy who come other water molecul with wavesof energy what water molecul emit/radiate. With this waves of energy water molecul get this waves of energy curving/bending right way there where water molecul is.







When water is 0 celsius and under, then expand/explod watermolecul logged to explod near by near.







Al that energy who go right to way next explod water molecul can push that water molecul strong way and thats why water expand faster that other stuff, when water get cooler!







When energy come more from outside and water get warm to 0 celsius to 4 celsius, then that outside energy, brake balance and that energy what watermolecul emit, cant go right away to next watermolecul and some go some other watermolecul who is behind next watermolecul.







Sapce dont expand or curv.







Nucleus of atoms is only energy that explod/expand all a time!







There is only one force and that force is PRESSURE. PUSH force.







changing of pressure and nothing else!

Space dont expand or curv, it WOBBLES!! (BUT IT DON'T FALL DOWN!!)

Pressure of voices in my head PUSHING me to rant!


I can has cheezburger????
QubitTamer
5 / 5 (4) Jul 20, 2009
get a ball and poke it with a 3 foot stick. hold the stick outward and rotate. the point at which the stick enters the ball always faces you. it does so because the ball is not rotating which is, in effect, the same as the moon. the moon does not rotate.


Please do this experiment in the left lane of the higway nearest you if you need someone to tell you why the moon doesn't rotate, not even a bit... M O O N that spells MOON... (props to Steven King for that line from "The Stand")
lysdexia
not rated yet Jul 20, 2009
cool down -> cool up

it's -> its

Are vitrites quasicrýstals?
Ricochet
not rated yet Jul 21, 2009
cool down -> cool up



it's -> its



Are vitrites quasicrýstals?


Ya down wit OCD?
(Ya, you know me!)
VOR
5 / 5 (3) Jul 21, 2009
get a ball and poke it with a 3 foot stick. hold the stick outward and rotate. the point at which the stick enters the ball always faces you. it does so because the ball is not rotating which is, in effect, the same as the moon. the moon does not rotate.

Oh sorry, but u win the Egnorance prize for that one. You were right about a stick being involved, but its not located in a ball. Try Uranus.
Velanarris
5 / 5 (2) Jul 21, 2009
How did such a terrible poke at water expansion turn into such great commentary?
getgoa
1 / 5 (1) Jul 22, 2009
Resurfacing the ice in hockey should prove this already?
darrennie
not rated yet Jul 24, 2009
another question is why does the moon not rotate at all...not even a little bit.


robbor, it's called a synchronous rotation,
now back to topic ?
Celyn
not rated yet Jul 27, 2009
I think that could be the simplest way to explain the theory of water molecules expansion and contraction , the freezing. :)

http://www.skinnyasap.com/