American Physical Society Acta Medica Okayama 0031-9007 115 19 2015 Chiral Ordering in Supercooled Liquid Water and Amorphous Ice 197801 EN Masakazu Matsumoto Takuma Yagasaki Hideki Tanaka The emergence of homochiral domains in supercooled liquid water is presented using molecular dynamics simulations. An individual water molecule possesses neither a chiral center nor a twisted conformation that can cause spontaneous chiral resolution. However, an aggregation of water molecules will naturally give rise to a collective chirality. Such homochiral domains possess obvious topological and geometrical orders and are energetically more stable than the average. However, homochiral domains cannot grow into macroscopic homogeneous structures due to geometrical frustrations arising from their icosahedral local order. Homochiral domains are the major constituent of supercooled liquid water and the origin of heterogeneity in that substance, and are expected to be enhanced in low-density amorphous ice at lower temperatures. No potential conflict of interest relevant to this article was reported.

American Institute of Physics Acta Medica Okayama 00219606 150 4 2019 Phase diagram of ice polymorphs under negative pressure considering the limits of mechanical stability 041102 EN Takahiro Matsui Graduate School of Natural Science and Technology, Okayama University Takuma Yagasaki Research Institute for Interdisciplinary Science, Okayama University Masakazu Matsumoto Research Institute for Interdisciplinary Science, Okayama University Hideki Tanaka Research Institute for Interdisciplinary Science, Okayama University Thermodynamic and mechanical stabilities of various ultralow-density ices are examined using computer simulations to construct the phase diagram of ice under negative pressure. Some ultralow-density ices, which were predicted to be thermodynamically metastable under negative pressures on the basis of the quasi-harmonic approximation, can exist only in a narrow pressure range at very low temperatures because they are mechanically fragile due to the large distortion in the hydrogen bonding network. By contrast, relatively dense ices such as ice Ih and ice XVI withstand large negative pressure. Consequently, various ices appear one after another in the phase diagram. The phase diagram of ice under negative pressure exhibits a different complexity from that of positive pressure because of the mechanical instability. No potential conflict of interest relevant to this article was reported.

American Institute of Physics Acta Medica Okayama 0021-9606 150 21 2019 A Bayesian approach for identification of ice Ih, ice Ic, high density, and low density liquid water with a torsional order parameter 214504 EN Masakazu Matsumoto Research Institute for Interdisciplinary Science, Okayama University Takuma Yagasaki Research Institute for Interdisciplinary Science, Okayama University Hideki Tanaka Research Institute for Interdisciplinary Science, Okayama University An order parameter is proposed to classify the local structures of liquid and solid water. The order parameter, which is calculated from the O–O–O–O dihedral angles, can distinguish ice Ih, ice Ic, high density, and low density liquid water. Three coloring schemes are proposed to visualize each of the coexisting phases in a system using the order parameter on the basis of Bayesian decision theory. The schemes are applied to a molecular dynamics trajectory in which ice nucleation occurs following spontaneous liquid-liquid separation in the deeply supercooled region as a demonstration. No potential conflict of interest relevant to this article was reported.

American Institute of Physics Acta Medica Okayama 00219606 150 21 2019 Liquid-liquid separation of aqueous solutions: A molecular dynamics study 214506 EN Takuma Yagasaki Research Institute for Interdisciplinary Science, Okayama University Masakazu Matsumoto Research Institute for Interdisciplinary Science, Okayama University Hideki Tanaka Research Institute for Interdisciplinary Science, Okayama University In the liquid-liquid phase transition scenario, supercooled water separates into the high density liquid (HDL) and low density liquid (LDL) phases at temperatures lower than the second critical point. We investigate the effects of hydrophilic and hydrophobic solutes on the liquid-liquid phase transition using molecular dynamics simulations. It is found that a supercooled aqueous NaCl solution separates into solute-rich HDL and solute-poor LDL parts at low pressures. By contrast, a supercooled aqueous Ne solution separates into solute-rich LDL and solute-poor HDL parts at high pressures. Both the solutes increase the high temperature limit of the liquid-liquid separation. The degree of separation is quantified using the local density of solute particles to determine the liquid-liquid coexistence region in the pressure-temperature phase diagram. The effects of NaCl and Ne on the phase diagram of supercooled water are explained in terms of preferential solvation of ions in HDL and that of small hydrophobic particles in LDL, respectively. No potential conflict of interest relevant to this article was reported.

American Institute of Physics Acta Medica Okayama 00219606 151 2019 Formation of Hot Ice Caused by Carbon Nanobrushes 064702 EN Takuma Yagasaki Research Institute for Interdisciplinary Science, Okayama University Masaru Yamasaki Graduate School of Natural Science and Technology, Okayama University Masakazu Matsumoto Research Institute for Interdisciplinary Science, Okayama University Hideki Tanaka Research Institute for Interdisciplinary Science, Okayama University Confinement in nanoscaled porous materials changes properties of water significantly. We perform molecular dynamics simulations of water in a model of a nanobrush made of carbon nanotubes. Water crystallizes into a novel structure called dtc in the nanobrush when (6,6) nanotubes are located in a triangular arrangement, and there is a space that can accommodate two layers of water molecules between the tubes. The mechanism of the solidification is analogous to formation of gas hydrates: hydrophobic molecules promote crystallization when their arrangement matches ordered structures of water. This is supported by a statistical mechanical calculation, which bears resemblance to the theory on the clathrate hydrate stability. No potential conflict of interest relevant to this article was reported.