The Strangeness of Water

Normal water is characterized by being one of the fluids with anomalous behaviour. On the other hand, possibly thanks to its anomalies, it is a basic substance for life. Recent research results show that the structural change of water on the nanoscale could explain its macroscopic anomalies.

In a recent study published in Scientific Reports, an online and open access journal from the publishers of Nature, in which the researcher Giancarlo Franzese, from the Department of Fundamental Physics at the University of Barcelona, has participated, the behaviour of water at extremely low temperature and high pressure was simulated. The results showed evidence, on the nanoscale, that in water there co-exist two liquid states of different density and energy which respond to different molecular configurations and which could be the reason for the anomalies that this fluid presents.

In this research, carried out in collaboration with researchers from the Swiss Federal Institute of Technology in Zurich (ETH Zurich); Yeshiva University, in New York, and Boston University, the simulations, which are difficult to develop experimentally, have shown evidence that on the nanoscale water molecules have many ways of combining among themselves, meaning that they exhibit different configurations which, in conditions of suitable temperature and pressure, change from one type of configuration to another in nanoseconds.

The two configurations detected are characterized by different densities and energy. So it is observed that the less density substances have the more energy they have. For this reason, when temperature is reduced, in general, the density increases. However, in the case of water, less density corresponds to less energy. This peculiar property shows itself in a clear way in extreme conditions, very close to the point when water forms amorphous ice, and when, according to the researchers, there exists a separation between a lighter, lower energy phase of water and another phase of water which is heavier and has more energy.

Far from these extreme conditions, these configurations of different density and energy survive on the nanoscale and compete with each other, constantly fluctuating and resulting, according to the researchers, in the macroscopic anomalies of water. According to Franzese, from the Faculty of Physics of the UB, affiliated to the BKC, “the consequences of this phenomenon could be decisive in the biological processes, owing to the fact that fluctuations among the different configurations could be the origin, for example, of the fluctuations that permit proteins to function”.