There are two states of liquid water, says an international team of physicists led by Oxford University’s Dr. Laura Maestro.
L.M. Maestro et al find that two states of liquid water play an important role in the thermal and optical properties of nanomedical systems; the team’s preliminary findings also suggest that the structure of liquid water strongly influences the thermal stability of proteins. Image credit: Martin Str.
Writing in the International Journal of Nanotechnology, Dr. Maestro and co-authors explain how the physical and chemical properties of water have been extensively studied for over 100 years and revealed some odd behavior not seen in other substances.
For instance, when water freezes it expands. By contrast, almost every other known substance contracts when it is cooled.
Water also exists as solid, liquid and gas within a very small temperature range (100 degrees Celsius) whereas the melting and boiling points of most other compounds span a much greater range.
Many of water’s bizarre properties are due to the molecule’s ability to form short-lived connections with each other known as hydrogen bonds.
There is a residual positive charge on the hydrogen atoms in the V-shaped water molecule either or both of which can form such bonds with the negative electrons on the oxygen atom at the point of the V.
This makes fleeting networks in water possible that are frozen in place when the liquid solidifies. The bonds are so short-lived that they do not endow the liquid with any structure or memory, of course.
Dr. Maestro and her colleagues from Spain and Mexico have looked closely at a variety of physical properties of liquid water, including thermal conductivity, proton spin-lattice relaxation time, refractive index, conductivity, surface tension and the piezo-optical coefficient.
They have found that these phenomena seem to flip between two particular characters at around 50 degrees Celsius, give or take 10 degrees, i.e. from 40 to 60 degrees Celsius.
“With the exception of piezo-optical coefficients, we observe a bilinear dependence defining a crossover temperature: approximately 64 degrees Celsius for thermal conductivity, about 50 degrees Celsius for proton spin-lattice relaxation time, 50 degrees Celsius for refractive index, about 53 degrees Celsius for conductivity, and 57 degrees Celsius for surface tension,” the scientists explained.
“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.”
Other properties of liquid water also show variations in this temperature range.
“It was recently reported that the thermal expansion coefficient presents a crossover temperature at 42 degrees Celsius and, at the same temperature, the isothermal compressibility shows a minimum,” the researchers said.
“Note that the speed of sound in liquid water, which is correlated with the thermal expansion coefficient, also presents a maximum at approximately 60 degrees Celsius.”
“These results confirm the existence of a crossover in the behavior of water that is probably related to the presence of two different liquid states with a temperature shift lying in a broad range between approximately 40 and 60 degrees Celsius.”
The two states in liquid water could have important implications for studying and using nanoparticles where the character of water at the molecule level becomes important for the thermal and optical properties of such particles.
Moreover, the preliminary findings suggest that the structure of liquid water can strongly influence the stability of proteins and how they are denatured at the crossover temperature, which may well have implications for understanding protein processing in the food industry but also in understanding how disease arises when proteins misfold.
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L.M. Maestro et al. 2016. On the existence of two states in liquid water: impact on biological and nanoscopic systems. International Journal of Nanotechnology 13: 8-9; doi: 10.1504/IJNT.2016.079670
