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Among all fluids, water has always been of special concern for scientists from a broad variety of research fields due to its rich behavior. In particular, some questions remain unanswered nowadays concerning the temperature dependence of bulk and interfacial transport properties of supercooled and liquid water, e.g. regarding the fundamentals of the violation of the Stokes-Einstein relation in the supercooled regime or the subtle relation between structure and dynamical properties. Here we investigated the temperature dependence of the bulk transport properties from ab initio molecular dynamics based on density functional theory, down to the supercooled regime. We determined from a selection of functionals, that SCAN better describes the experimental viscosity and self-diffusion coefficient, although we found disagreements at the lowest temperatures. For a limited set of temperatures, we also explored the role of nuclear quantum effects on water dynamics using ab initio molecular dynamics that has been accelerated via a recently introduced machine learning approach. We then investigated the molecular mechanisms underlying the different functionals performance and assessed the validity of the Stokes-Einstein relation. We also explored the connection between structural properties and the transport coefficients, verifying the validity of the excess entropy scaling relations for all the functionals. These results pave the way to predict the transport coefficients from the radial distribution function, helping to develop better functionals. On this line, they indicate the importance of describing the long-range features of the radial distribution function., Comment: 10 pages, 5 figures

The search for materials with high thermal resistance has promising applications in thermoelectric devices and boiling crisis retardation. In this paper, we study the interfacial heat transfer between water and gold, nanostructuring the gold surface and coating it with graphene. By trapping air (or vacuum in our simulations) between graphene and the nanopatterned surface, we observe a considerable increase in the interfacial resistance compared to the planar gold situation, which is shown to scale with the effective graphene–gold contact surface for both monolayer and multilayer graphene. With the massive thermal resistances we predict (up to 200 nm in terms of Kapitza length), the system proposed here represents a robust alternative to superhydrophobic Cassie materials. Moreover, since the low thermal conductance is achieved primarily due to geometry (vacuum trapping), it is straightforward to extend our results to any material with a structure equivalent to that of the nanopatterned gold wall considered here.