The inhomogeneous structure of water at ambient conditions
2009 (English)In: PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA, ISSN 0027-8424, Vol. 106, no 36, 15214-15218 p.Article in journal (Refereed) Published
Small-angle X-ray scattering (SAXS) is used to demonstrate the presence of density fluctuations in ambient water on a physical length-scale of approximate to 1 nm; this is retained with decreasing temperature while the magnitude is enhanced. In contrast, the magnitude of fluctuations in a normal liquid, such as CCl4, exhibits no enhancement with decreasing temperature, as is also the case for water from molecular dynamics simulations under ambient conditions. Based on X-ray emission spectroscopy and X-ray Raman scattering data we propose that the density difference contrast in SAXS is due to fluctuations between tetrahedral-like and hydrogen-bond distorted structures related to, respectively, low and high density water. We combine our experimental observations to propose a model of water as a temperature-dependent, fluctuating equilibrium between the two types of local structures driven by incommensurate requirements for minimizing enthalpy (strong near-tetrahedral hydrogen-bonds) and maximizing entropy (non-directional H-bonds and disorder). The present results provide experimental evidence that the extreme differences anticipated in the hydrogen-bonding environment in the deeply supercooled regime surprisingly remain in bulk water even at conditions ranging from ambient up to close to the boiling point.
Place, publisher, year, edition, pages
2009. Vol. 106, no 36, 15214-15218 p.
density fluctuations, liquid-liquid hypothesis, small angle X-ray scattering, water structure, X-ray spectroscopy
IdentifiersURN: urn:nbn:se:liu:diva-20741DOI: 10.1073/pnas.0904743106OAI: oai:DiVA.org:liu-20741DiVA: diva2:235962
C Huang, K T Wikfeldt, T Tokushima, D Nordlund, Y Harada, U Bergmann, M Niebuhr,
T M Weiss, Y Horikawa, M Leetmaa, M P Ljungberg, O Takahashi, Annika Lenz,
Lars Ojamäe, A P Lyubartsev, S Shin, L G M Pettersson and A Nilsson, The inhomogeneous structure of water at ambient conditions, 2009, PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA, (106), 36, 15214-15218.
Copyright: National Academy of Sciences