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CICLE DE SEMINARIS SOBRE LÍQUIDS MOLECULARS I SOLUCIONS IÒNIQUES


 

SPEAKER: Valentino Bianco (Universitat de Barcelona)
TITLE: Hydrophobic confinement: effect on a supercooled water monolayer.
DATE / PLACE: 12pm March 6th in the seminar room B4-212
ABSTRACT:
Water is extremely important for life and, at the same time, very anomalous with respect to simple substances. Different theories have been proposed in order to explain tho origin of  such anomalies. A way to discriminate between these theories is to analyze, with  experiments and simulations, the behavior of metastable supercooled water. In particular it has been suggested that water under confinement at low temperatures could be related to highly supercooled bulk water.
We contribute to the debate by analyzing the behavior of  a water monolayer confined between  hydrophobic walls. By efficient Monte Carlo simulations we are able to simulate extremely large systems for extremely long time scales, finding the anomalies and relating them to the low temperature phase diagram. We find a first order phase transition line separating two metastable liquids: the high-density liquid (HDL) at higher temperatures and pressures and the low-density liquid (LDL) at lower temperatures and pressures. Such line ends in a liquid-liquid critical point (LLCP). By finite size scaling of the appropriate order parameter, we find that the LLCP belongs to the universality class of the two-dimensional (2D) Ising model in the limit of infinite walls. However, for wall sizes up to fifty times larger than the monolayer thickness h, the LLCP is better described by the 3D Ising model universality class, something unexpected based on studies for simple liquids. We ascribe this result to the strong cooperativity and the low coordination number of the hydrogen bond network.