Water is an essential element for all forms of life; it is the basis of ecosystems and constitutes a large part of our body, as well as that of other animals and plants.

A water molecule, whose chemical formula is H₂O, consists of one atom of oxygen and two of hydrogen. Oxygen is more electronegative than hydrogen, therefore it attracts the bonding electrons towards the vertex of the water molecule, which thus shows a negative partial electric charge, while the ends a positive partial charge (electric dipole).

The unequal distribution of electrical charges means that the entire molecule has a polarity that allows it to attract and be attracted to other molecules. This attraction, called a hydrogen bond, is the basis for the interpretation of many of the typical properties that make it a unique substance on Earth, still in some ways unknown and therefore the subject of much scientific research.

In a new paper, the research team coordinated by Fabrizio Frezza of the Department of Information Engineering, Electronics and Telecommunications of Sapienza University of Rome has experimentally demonstrated that the electrical properties of the liquid of life (and other aqueous solutions) can only be explained if the water is described as a mixture of two fluids, with different structural and thermodynamic characteristics. The study, carried out in collaboration with ENEA's Physical Technologies for Safety and Health Division and the CNR's Institute of Complex Systems, has been published on the journal Physics Letters A.

The starting point of the analysis has been the two-fluid model, according to which liquid water is made up of two non-separable components: one high-density and one low-density. The origin of the two fluids is to be found in the existence of a fundamental state, predicted by quantum field theory, which involves many tens of molecules at the same time. The interaction generated in this fundamental state describes a collective behaviour and can be considered the theoretical basis of hydrogen bonding.

Subsequently, the researchers experimentally determined the relative percentages of the two different fluids through spectroscopic measurements, observing that they vary according to the temperature of the liquid and are modified by the presence of other substances dissolved in water.

"We have thus observed − says Fabrizio Frezza − that the relative percentages of these two fluids influence the polarizability of water. This makes it possible, for the first time, to predict the dielectric response of water with an analytical calculation and to design new materials to maximise signal transmission through water-based media."

The outcomes of the study add an important piece to the description of water as a two-fluid system even at room temperature and not only at very low temperatures, as recently proved by computer simulations. The latter observation can be of great interest for applications in the biological field such as the study of protein folding (the three-dimensional structure of proteins that determines their functionality) and the dielectric properties of biological matrices that determine the interactions between environmental electromagnetic fields and stability of living systems.

References:

Dielectric permittivity of aqueous solutions of electrolytes probed by THz time-domain and FTIR spectroscopy − A. De Ninno, E. Nikollari, M. Missori e F. Frezza − Physics Letters A, 2020. DOI: https://doi.org/10.1016/j.physleta.2020.126865

Further Information

Fabrizio Frezza 
Department of Information Engineering, Electronics and Telecommunications
fabrizio.frezza@uniroma1.it