Study of percolation and clustering in supercritical water-CO2 mixtures

The microscopic structure of supercritical water-CO2 mixture is investigated by neutron diffraction experiments exploiting the isotopic H/D substitution. The investigated water reach mixtures are in the liquidlike region of the phase diagram, according to the behavior of the radial distribution functions, yet a reduction of the average number of hydrogen bonds, compared to equivalent states of pure water, is found. As a consequence, the average dimension of water clusters is reduced and the system stays below the percolation threshold. These results, along with the shift of the main peaks of the site-site radial distribution functions, suggest that the excess volume in these supercritical mixtures is likely associated with the CO2 solvation shell. (c) 2008 American Institute of Physics.