New research reveals hitherto-unknown state of liquid water


You’d think that we already know everything there is to know about water, a compound that makes up nearly 60-percent of our body. Turns out there’s more to it than meets the eye. As part of a new study, for instance, scientists have discovered a second, hitherto-unknown state of liquid water, achieved when heated to temperatures between 40 and 60 degrees Celsius. According to the researchers, there seems to be a “crossover temperature”, at which the substance undergoes a change in state.

Up until now, water was believed to exist in three basic states: solid, liquid and gas. Despite being one of the most abundant compounds on Earth, it boasts several impressive characteristics, including the highest surface tension among all liquids. Unlike most other substances, water’s solid state is capable of floating on its liquid state and, is known to expand when frozen.

Compared to other hydrides like hydrogen sulfide and hydrogen telluride, whose boiling points decrease with decreasing molecular size, H2O has a very high boiling point despite having a small molecule weight. Speaking about the study, Philip Ball writes in Nature:

No one really understands water. It’s embarrassing to admit it, but the stuff that covers two-thirds of our planet is still a mystery. Worse, the more we look, the more the problems accumulate: new techniques probing deeper into the molecular architecture of liquid water are throwing up more puzzles.

According to the new discovery, liquid water exhibits two states, when heated between temperatures of around 40 and 60 degrees Celsius (approx. 104 and 140 degrees Fahrenheit). To uncover the findings, an international team, led by Laura Maestro of Oxford University, studied the different properties of water, such as thermal conductivity, electrical conductivity, dielectric constant, surface tension and refractive index. They also examined the responses H2O has to varying temperatures between 0 and 100 degrees Celsius.

When heated beyond 40 degrees Celsius, these properties seemed to change gradually until about 60 degrees Celsius. Within this range, the team explained, each property came with a different “crossover temperature”: 50 degrees Celsius for refractive index, 57 for surface tension, 64 degrees Celsius for thermal conductivity and finally, 53 for electrical conductivity. The scientists added:

These results confirm that in the 0-100 degrees Celsius range, liquid water presents a crossover temperature in many of its properties close to 50 degrees Celsius.

The discovery, as pointed out by the researchers, could explain the various unusual properties water has. Two or more water molecules are held together by means of weak, short-lived bondsthat are in fact a lot more feeble than the connections binding hydrogen and oxygen atoms together within a molecule. The former is constantly undergoing changes, which in turn H2O many of its strange properties. Ball goes on to say:

Everyone is agreed that one aspect of water’s molecular structure sets it apart from most other liquids: fleeting hydrogen bonds. These feeble bonds that link the molecules constantly break and form above water’s melting point, yet still impose a degree of structure on the molecular jumble. That’s where the consensus ends.

Recently published in the International Journal of Nanotechnology, the discovery could greatly enhance our understanding of biological as well as nanoscale systems. The team states:

For example, the optical properties of metallic (gold and silver) nanoparticles dispersed in water, used as nanoprobes, and the emission properties of … quantum dots, used for fluorescence bioimaging and tumor targeting, show a singular behavior in this temperature range. [It also] raises the question of whether temperature-driven structural changes in water affect biological macromolecules in aqueous solutions, and in particular in proteins, which are the vital functional biological units in living cells.

Source: Nature

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