Thermodynamic response functions and Stokes-Einstein breakdown in superheated water under gigapascal pressure

Abstract

Liquid water is the most intriguing liquid in nature, both because of its importance to every known form of life, and its numerous anomalous properties, largely magni ed under supercooled conditions. Among the anomalous properties of water is the seeming divergence of the thermodynamic response functions and dynamic properties below the homogenous nucleation temperature (~232 K). Furthermore, water exhibits an increasingly decoupling of the viscosity and diffusion, upon cooling, resulting in the breakdown of the Stokes-Einstein relationship (SER). At high temperatures and pressures, however, water behaves more like a "simple" liquid. Nonetheless, experiments at 400 K and GPa pressures (Bove et al. (2011) Phys. Rev. Lett., 111:185901) showed that although the diffusion decreases monotonically with the pressure, opposite to pressurized supercooled water, a decoupling of the viscosity and diffusion, larger than that found in supercooled water at normal pressure, is observed. Here, we studied the thermodynamic response functions and breakdown of the SER along the 400 K isotherm up to 3 GPa, through molecular dynamics. Seven water models were investigated. A monotonic increase of the density (~50 %) and decrease of the isothermal compressibility (~90 %) and thermal expansion (~65 %) is found. Our results also show that compressed hot water has various resemblances to cool water at normal pressure, with pressure inducing the formation of a new second coordination sphere and a monotonic decrease of the diffusion and viscosity coe cients. Whereas all water models provide a good account of the viscosity, the magnitude of the violation of the SER at high pressures (> ~1 GPa) is signi cantly smaller than that found through experiments. Thus, violation of the SER in simulations is comparable to that observed for liquid supercooled water, indicating possible limitations of the water models to account for the local structure and self-diffusion of superheated water above ~1 GPa.

Laterally Heterogeneous Structure and Dynamics of Water and Ion inside a Nanochannel of a Covalent Organic Framework Membrane Designed for Osmotic Energy Conversion

“…For this, we calculate two-dimensional profile of hydrogen (H−)-bond number between water molecules N H ‑ bond , presented in Figure B for COF –3 . An H-bond between two water molecules is defined by the standard criteria, r O D O A < 3.5 Å and ∠H D O D O A < 30°, where “D” and “A” stand for the H-bond donor and acceptor molecules, respectively. − As expected, the first hydration layer of the channel wall has lower number of H-bond. At the center of the channel, the number of H-bonds per water molecule is ∼3.6, which is expected for bulk water.…”

Anomalous lateral diffusion of lipids during the fluid/gel phase transition of a lipid membrane

“…The previous work was authored by one of us, where the non-Gaussian displacement distribution was observed in a raft mimetic membrane having liquid-ordered (L o ) and liquid-disordered (L d ) phases coexisting together. 127 It was also found that the FnGD behaviour could be explained both by the ''diffusing diffusion'' picture, 184 and the translational jump-diffusion (TJD) model, 127 previously employed to explain the diffusion-viscosity decoupling in supercooled water 130,134,[185][186][187][188][189] and aqueous solution. 131,132,135,136,190 Interestingly, similar FnGD behaviour was not observed for the pure L o and L d phases of the membrane.…”