Copyrtght Nature
Copyrtght Nature

1) Ambient and Supercooled Water

It is known since several decades that many properties of water such density, compressibility, heat capacity etc. become strongly anomalous as the temperature decreases. In particular, this deviation from a simple liquid behaviour becomes strongly enhanced as water is cooled below the freezing point into the metastable supercooled regime. Some of these properties seem to diverge around a mysterious temperature of 228 K and different theories have been proposed to explain this unusual behaviour. One of the most popular and that we are currently investigating with experimental techniques is the liquid-liquid transition (LLT) and liquid-liquid critical point (LLCP) model. Here we base our studies on using x-ray lasers to investigate deep supercooled water on timescales that is shorter than time for ice nucleation. It is also important to realize that the anomalous regime already occurs at much warmer temperatures even above room temperature. We are, therefore, also investigating water in the stable regime with an overall aim to establish a unified understanding of water from hot to deep supercooled conditions using synchrotron radiation. Here the hypothesis is that water at ambient temperature encompasses fluctuations around two local structures and that the dominating structure is a strongly distorted H-bonded environment but the tetrahedral local structure that are organised in small patches grows in population and size with decreasing temperature. The experimental effort is supported by theoretical investigations.

Some important publications:

The Structure of the First Coordination Shell in Liquid Water, P. Wernet, D. Nordlund, U. Bergmann, H. Ogasawara, M. Cavalleri, L.Å. Näslund, T. K. Hirsch, L. Ojamäe, P. Glatzel, M. Odelius, L.G.M. Pettersson, and A. Nilsson. Science 304 (2004) 995.

High Resolution X-ray Emission Spectroscopy of Liquid Water: the Observation of Two Structural Motifs T. Tokushima, Y. Harada, O. Takahashi, Y. Senba, H. Ohashi, L.G.M. Pettersson, A. Nilsson, and S. Shin. Chem. Phys. Lett. 460 (2008) 387

Diffraction and IR/Raman Data Do Not Prove Tetrahedral Water M. Leetmaa, K. T. Wikfeldt, M. P. Ljungberg, M. Odelius, J. Swenson, A. Nilsson, and L. G.M. Pettersson. J. Chem. Phys 129 (2008) 084502

On the Range of Water Structure Models Compatible with X-ray and Neutron Diffraction Data K. T. Wikfeldt, M. Leetmaa, M. P. Ljungberg, A. Nilsson, and L. G.M. Pettersson. J. Phys. Chem. B 113 (2009) 6246

The Inhomogeneous Structure of Water at Ambient Conditions 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, A. Lenz, L. Ojamäe, A. P. Lyubartsev, S. Shin, L. G. M. Pettersson and A. Nilsson Proc. Natl. Acad. Sci. USA 106 (2009) 15214

Increasing correlation length in bulk supercooled H2O, D2O and NaCl solution determined from small angle x-ray scattering C. Huang, T. M. Weiss, D. Nordlund, K. T. Wikfeldt, L. G. M. Pettersson and A. Nilsson J. Chem. Phys. 133 (2010) 134504

Spatially inhomogeneous bimodal inherent structure in simulated liquid water K. T. Wikfeldt, A. Nilsson and L. G. M. Pettersson Phys. Chem. Chem. Phys. 13, 19918 (2011).

Wide-Angle X-ray Diffraction and Molecular Dynamics Study of Medium-Range Order in Ambient and Hot Water C. Huang, K. T. Wikfeldt, D. Nordlund, U. Bergmann, T. McQueen, J. Sellberg, L. G. M. Pettersson and A. Nilsson Phys. Chem. Chem. Phys. 13 (2011) 19997

Ab initio van der Waals Interactions in Simulations of Water Alter Structure from Mainly Tetrahedral to High-Density-Like A. Møgelhøj, A. K. Kelkkanen, K. T. Wikfeldt, J. Schiøtz, J. J. Mortensen, L. G.M. Pettersson, B. I. Lundqvist, K. W. Jacobsen, A. Nilsson, and J. K. NØrskov J. Phys. B. 115 (2011) 14149

Benchmark oxygen-oxygen pair-distribution function of ambient water from x-ray diffraction measurements with a wide Q-range L. Skinner, C. Huang, D. Schlesinger, L. G. M. Pettersson, A. Nilsson and C. J. Benmore J. Chem. Phys. 138 (2013) 074506.

Ultrafast X-ray probing of water structure below the homogeneous ice nucleation temperature J. A. Sellberg, C. Huang, T. A. McQueen, N. D. Loh, H. Laksmono, D. Schlesinger, R. G. Sierra, D. Nordlund, C. Y. Hampton, D. Starodub, D. P. DePonte, M. Beye, C. Chen, A. V. Martin, A. Barty, K. T. Wikfeldt, T. M. Weiss, C. Caronna, J. Feldkamp, L. B. Skinner, M. M. Seibert, M. Messerschmidt, G. J.Williams, S. Boutet, L. G. M. Pettersson, M. J. Bogan and A. Nilsson Nature 510, 381 (2014)

Anomalous Behavior of the Homogeneous Ice Nucleation Rate in “No-Man’s Land” H. Laksmono, T. A. McQueen, J. A. Sellberg, N. D. Loh, C. Huang, D. Schlesinger, R. G. Sierra, C. Y. Hampton, D. Nordlund, M. Beye, A. V. Martin, A. Barty, M. M. Seibert, M. Messerschmidt, G. J. Williams, S. Boutet, K. Amann-Winkel, T. Loerting, L. G. M. Pettersson, M. J. Bogan, and A. Nilsson J. Phys. Chem. Lett. 6, 2826 (2015)

Review Papers and Book Chapters:

Perspective on the Structure of Liquid Water A. Nilsson and L. G. M. Pettersson Chem. Phys. 389 (2011) 1.

Fluctuations in Ambient Water A. Nilsson, C. Huang and L.G. M. Pettersson J. Mol. Liq. 176 (2012) 2.

The Structure of Water: from Ambient to Deeply Supercooled L. G. M. Pettersson and A. Nilsson J. Non-Crysts Solids 407, 399 (2015).

X-ray Spectroscopy, Scattering and Simulation Studies of Instantaneous Structures in Water A. Nilsson , D. Schlesinger and L. G. M. Pettersson

Water: Fundamental as the Basis for Understanding the Environment and Promoting Technology, Ed P. G. Debenedetti, M. A. Ricci and F. Bruni, Proceedings of the International School of Physics “ Enrico Fermi”, IOS press.

The structural origin of Anomalous properties of liquid water A. Nilsson and Lars G. M. Pettersson Nature Comm. 6, 8998 (2015)


2) Glassy Water

To explain the origin of water´s anomalies, different theories and scenarios have been discussed controversially over the last 30 years. Experimental studies of the solid states of water are a key for better understanding of the properties of water. In particular the study of the amorphous (glassy) states of ice are important.

Amorphous ice can be prepared in many different ways. The most direct way might be deposition of water vapour on a cold substrate, as happening in nature on interstellar dust grains and first successfully prepared in the lab by Burton and Oliver in 1935. The prepared ice is called amorphous solid water (ASW). Depending on the preparation specifications ASW is a highly porous material, but after sufficient annealing has the same density and structure of low-density amorphous ice (LDA).

Mishima et al. succeeded to prepare high-density amorphous ice in 1984 by compression of hexagonal ice at 77 K to 1.6 GPa. They also showed that HDA undergoes a first order transition to an amorphous form of lower density (LDA). Since that discovery it is highly debated if the two amorphous states HDA and LDA are directly connected to two liquid states of water LDL and HDL.

For low-density amorphous ices a glass transition onset temperature of ~136 K was detected by following the change in heat capacity upon heating LDA ice at ambient pressure with a rate of 10 K/min (Johari, Mayer et al. 1987). The real nature of this very feeble signal has been discussed over decades. For HDA the glass transition at ambient pressure has been detected at ~116 K using calorimetry and dielectric spectroscopy as well (Amann-Winkel et al. 2013).

Although recent measurements give considerable support for the liquid-liquid theory, the topic is still debated controversially in literature. Our group is now going to study the origin of these glass-to-liquid transitions using X-ray scattering as well as X-ray Photon Correlation Spectroscopy (XPCS).


3) Dynamics

With the development of ultrafast x-ray lasers which provide coherent beams, a new domain for x-ray diffraction of disordered materials becomes possible which can be used to probe the water dynamics on a molecular level. Using X-ray Photon Correlation Spectroscopy (XPCS) we investigate the true ground state equilibrium dynamics of water, which range from 10-100s of femtoseconds in liquid water under ambient conditions down to seconds near the glass transition. The dynamical content is encoded in the speckle pattern and reflects motion in reciprocal space. By varying the scattering geometry from small angle x-ray scattering (SAXS) to wide angles (WAXS) one can additionally implement spatial resolution and further resolve structurally the dynamical heterogeneities, which range from neighboring water molecules to larger domains in the order of 10-100 nm.