The origin of water's range properties

Water, an element that is common and necessary for life on earth, has properties that are different from other substances. How water's density, specific heat, viscosity, and compressibility respond to changes in temperature and pressure is completely opposite to liquids that we know. For instance, the water that has the temperature higher than 4 degrees Celsius increases density when it is cooled down. This is not different from the properties of other liquids. However, when the temperature of the water is below 4 degrees Celsius, its density decreases when it is cooled. This unique property of the water explains why ice floats on the surface of the water instead of sinking to the bottom. Normally, the solid state of a substance should have a higher density than its liquid state. Since the density of the water decrease when it is cooled under 4 degrees Celsius, its solid form has a lower density than its liquid form. When you put an object that has a lower density than that of the water, it floats on the surface. That is why we see ice cubes float on the top of the water in a glass of ice water.

After knowing that water behaves strongly below 4 degrees Celsius, you may wonder if this strangeness had the limit. How cold the water should be when it stops behaving strangely you might ask. Researchers at Stockholm University use x-ray laser to observe the water and figured out how water fluctuates between two different states when it is cooled. They found out that water can exists in two different liquid states that have different ways to bond molecules. Water fluctuates between these states and the fluctuation reaches the maximum at - 44-degree Celsius. The ability of the water to shift between two different states gives it its unusual properties. As the water cools down, the strangeness increase because of the fluctuation increases.

To observes the liquid water at a temperature below the freezing point of the water, researchers had to  "supercool" the water. Supercooling means cooling down a liquid below its freezing point without making it become solid. To understand how supercooling works, we have to understand how a liquid becomes solid. As the temperature of a liquid drop, its molecules movement become slower. When the velocity of the molecules becomes very low, they have more chance to bond with each other and form a solid. However, the low velocity of the molecules does not guarantee the formation of the solid. To form a solid, the presence of a nucleus around which a crystal structure can be formed is essential. Without the nucleus, a liquid can't be crystallized and become solid. Therefore, supercooling of the water can be achieved by preventing the presence of such nucleus. To supercool the water, we must purify the water since the minerals in the water provide the nucleus and allow the water to crystallize. Moreover, a sudden rupture of the water should be avoided since the rupture may allow molecules to cluster and form a nucleus. In fact, there is no professional technique required to make supercool water. We can make supercool water at home by putting the purified water in the freezer and take it out after about two hours. If you make the supercool water successfully, you will see that bottle of water turns to ice suddenly when you shake the bottle.