研究者詳細 - 松本　正和

Structure, dynamics and thermodynamic stability of high-pressure ices and clathrate hydrates 査読

Yagasaki, T., Himoto, K., Nakamura, T., Matsumoto, M., Tanaka, H.

Molecular Simulation 41 ( 10-12 ) 868 - 873 2015年

Effects of thermodynamic inhibitors on the dissociation of methane hydrate: A molecular dynamics study 査読

Yagasaki, T., Matsumoto, M., Tanaka, H.

Physical Chemistry Chemical Physics 17 ( 48 ) 32347 - 32357 2015年

Spin-One Ising Model for Ice VII-Plastic Ice Phase Transitions 査読

Masakazu Matsumoto, Kazuhiro Himoto, Hideki Tanaka

JOURNAL OF PHYSICAL CHEMISTRY B 118 ( 47 ) 13387 - 13392 2014年11月

担当区分：筆頭著者,　責任著者記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：AMER CHEMICAL SOC

We propose a spin model compatible with ice VII-plastic ice phase transitions and critical phenomena discovered recently by computer simulations. The Blume-Capel spin-1 Ising model is extended in order to describe the entropic stabilization effect in the plastic ice phase. The model shares the same set of tricritical exponents with simulation, indicating that they are of the same universality class.

DOI： 10.1021/jp5049502

Dissociation of Methane Hydrate in Aqueous NaCl Solutions 査読

Takuma Yagasaki, Masakazu Matsumoto, Yoshimichi Andoh, Susumu Okazaki, Hideki Tanaka

JOURNAL OF PHYSICAL CHEMISTRY B 118 ( 40 ) 11797 - 11804 2014年10月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：AMER CHEMICAL SOC

Molecular dynamics simulations of the dissociation of methane hydrate in aqueous NaCl solutions are performed. It is shown that the dissociation of the hydrate is accelerated by the formation of methane bubbles both in NaCl solutions and in pure water. We find two significant effects on the kinetics of the hydrate dissociation by NaCl. One is slowing down in an early stage before bubble formation, and another is swift bubble formation that enhances the dissociation. These effects arise from the low solubility of methane in NaCl solution, which gives rise to a nonuniform spatial distribution of solvated methane in the aqueous phase. We also demonstrate that bubbles form near the hydrate interface in dense NaCl solutions and that the hydrate dissociation proceeds inhomogeneously due to the bubbles.

DOI： 10.1021/jp507978u

Spontaneous liquid-liquid phase separation of water 査読

Takuma Yagasaki, Masakazu Matsumoto, Hideki Tanaka

PHYSICAL REVIEW E 89 ( 2 ) 020301 2014年2月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：AMER PHYSICAL SOC

We report a molecular dynamics simulation demonstrating a fast spontaneous liquid-liquid phase separation of water and a subsequent slow crystallization to ice. It is found that supercooled water separates rapidly into low-and high-density domains so as to reduce the surface energy in the rectangular simulation cell at certain thermodynamic states. The liquid-liquid phase separation, which is about two orders of magnitude faster than the crystallization, suggests a possibility to observe this phenomenon experimentally.

DOI： 10.1103/PhysRevE.89.020301

Effect of Bubble Formation on the Dissociation of Methane Hydrate in Water: A Molecular Dynamics Study 査読

その他リンク： http://orcid.org/0000-0002-4969-4715

Takuma Yagasaki, Masakazu Matsumoto, Yoshimichi Andoh, Susumu Okazaki, Hideki Tanaka

JOURNAL OF PHYSICAL CHEMISTRY B 118 ( 7 ) 1900 - 1906 2014年2月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：AMER CHEMICAL SOC

We investigate the dissociation of methane hydrate in liquid water using molecular dynamics simulations. As dissociation of the hydrate proceeds, methane molecules are released into the aqueous phase and eventually they form bubbles. It is shown that this bubble formation, which causes change in the methane concentration in the aqueous phase, significantly affects the dissociation kinetics of methane hydrate. A large system size employed in this study makes it possible to analyze the effects of the change in the methane concentration and the formation of bubbles on the dissociation kinetics in detail. It is found that the dissociation rate decreases with time until the bubble formation and then it turns to increase. It is also demonstrated that methane hydrate can exist as a metastable superheated solid if there exists no bubble.

DOI： 10.1021/jp412692d

水素を含む高圧氷の構造と熱力学的安定性招待査読

L. Hakimu, 矢ヶ﨑琢磨, 松本正和, 田中秀樹

高圧力の科学と技術 24 ( 4 ) 265 - 269 2014年

Yet another criticality of water 査読

Kazuhiro Himoto, Masakazu Matsumoto, Hideki Tanaka

PHYSICAL CHEMISTRY CHEMICAL PHYSICS 16 ( 11 ) 5081 - 5087 2014年

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：ROYAL SOC CHEMISTRY

A phase behavior around the transition between ice VII and a plastic phase of water is investigated by molecular dynamics simulation and the subsequent analysis on the basis of Landau theory. The prior works have predicted that the phase transition between ice VII and plastic ice is a first-order transition on the ground of a weak hysteresis and so on. A rigorous survey in the present report, however, augments their prediction with new evidence that a first-order phase transition line gives way to a second-order one at higher pressures, where a tricritical point joins these phase boundaries together. Critical phenomena are also observed whereby, other than that associated with the hypothetical critical point in the deeply supercooled state, which could influence the physical properties in a wide range of temperatures and pressures. A new critical behavior is affirmed by the result that the scaling law holds at any pressure on the second-order phase transition line for which the critical exponents are estimated. We introduce an appropriate order parameter to obtain the Landau free energy functional and the change in the functional against temperature accounts for the phase behaviors. This also enables an estimate of the coexistence and the spinodal lines at pressures below the tricritical point, all of which compensate those obtained directly by molecular dynamics simulations. These results allow us to anticipate that the critical fluctuations may give us a clue for determining the phase boundary experimentally.

DOI： 10.1039/c3cp54726d

Diversity of transition pathways in the course of crystallization into ice VII 査読

Kenji Mochizuki, Kazuhiro Himoto, Masakazu Matsumoto

Phys. Chem. Chem. Phys. 16 ( 31 ) 16419 - 16425 2014年

担当区分：最終著者記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Royal Society of Chemistry (RSC)

<p>A new metastable ice phase is discovered in the freezing pathway into ice VII in accord with Ostwald's step rule.</p>

DOI： 10.1039/c4cp01616e

Defect pair separation as the controlling step in homogeneous ice melting. 査読

Mochizuki K, Matsumoto M, Ohmine I

Nature 498 ( 7454 ) 350 - 354 2013年6月

On the thermodynamic stability of hydrogen hydrates in the presence of promoter molecules 査読

Takato Nakayama, Masakazu Matsumoto, Hideki Tanaka

AIP Conference Proceedings 1568 46 - 52 2013年

記述言語：英語掲載種別：研究論文（国際会議プロシーディングス）出版者・発行元：American Institute of Physics Inc.

Cage occupancies of hydrogen molecules in a clathrate hydrate have been examined by means of semi-grand canonical Monte Carlo simulations where hydrogen molecules enter into or leave from it in the presence of promoter species. This kind of simulation allows to evaluate the thermodynamic stability via the chemical potential of water at a given temperature and pressure. In order to make a better estimation of the chemical potential, we adopt a different standard state from the corresponding empty one. It is revealed that the present method is indeed effective to minimize errors associated with the numerical simulations.

DOI： 10.1063/1.4848090

STATISTICAL MECHANICAL APPROACH TO THE THERMODYNAMIC STABILITY OF CLATHRATE HYDRATES 査読

Hideki Tanaka, Masakazu Matsumoto

LIQUID POLYMORPHISM 152 421 - 462 2013年

Rotational Dynamics of Plastic Ice 査読

Kazuhiro Himoto, Masakazu Matsumoto, Hideki Tanaka

JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 81 ( SUPPL. A ) 2012年9月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：PHYSICAL SOC JAPAN

A plastic phase predicted to exist between crystalline ice VII and liquid water has been investigated. The present work focuses on the dynamics of the water molecules in the phases at high temperature and pressure, i.e. ice VII, plastic ice, and liquid water. The hydrogen-bond correlation function providing the lifetime of hydrogen bonds is compared to the reorientational correlation function to examine a relation between a rotation of an individual molecule and an energetic relaxation process. The hydrogen-bond correlation function of plastic ice decays in a way similar to liquid but it converges to a finite value as seen in ice VII, reflecting the rotational motion of the water molecule at the fixed location. In addition, the relaxation times of the two correlation functions for plastic ice resemble one another, confirming the fact that only the rotational motion invokes the hydrogen-bond rearrangements in plastic ice.

On the Occupancy of Carbon Dioxide Clathrate Hydrates: Grandcanonical Monte Carlo Simulations 査読

Masato Matsuo, Yoshio Takii, Masakazu Matsumoto, Hideki Tanaka

JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 81 ( SUPPL. A ) 2012年9月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：PHYSICAL SOC JAPAN

Grandcanonical Monte Carlo simulations are performed in order to examine the cage occupancies of carbon dioxide clathrate hydrate in both the larger and the smaller cages, the latter of which has been controversial issue and is related significantly with its phase behavior. It is found that occupancy of CO2 in the smaller cage of clathrate structure I is negligible at a pressure of CO2 below 1 MPa while that in the larger cage increases gradually with increasing the pressure of CO2 in equilibrium with the clathrate hydrate. It is suggested by the present simulations that CO2 clathrate hydrate exhibits a different character in occupancy from ethane, which is a little larger than CO2 and cannot enter into the smaller cage.

Structure and Dynamics of Aqueous Solutions of Electrolytes in Confined Space 査読

Yoshimasa Yamakawa, Masakazu Matsumoto, Hideki Tanaka

JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 81 ( SUPPL. A ) 2012年9月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：PHYSICAL SOC JAPAN

We perform isothermal-isobaric molecular dynamics simulations of aqueous solutions of potassium and chloride ions with varying tube diameter. An equilibrium state is attained within 1 ns, but the relaxation time to equilibrium is dependent on the initial arrangement of ions. When the tube diameter is larger than 1 nm, ions exchange their axial positions in few tens of picosecond to be the most stable configuration in which counterions are lined up alternately. However, ions in a tube narrower than 1 nm cannot exchange the mutual positions in axial-coordinate within an order of nano second. The axial self-diffusion coefficients are also examined. It is found that they increase with increasing the tube size once an equilibrium is attained. These results suggest the partial hydration and dehydration play a certain role in diffusion of the electrolytes in confined space like tubes and channels.

Inclusion of Neon Inside Ice I-c and Its Influence to the Ice Structure 査読

Hakim Lukman, Matsumoto Masakazu, Koga Kenichiro, Tanaka Hideki

JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 81 ( SUPPL. A ) 2012年9月

Metastable Polymorphs of Clathrate Hydrate 査読

Masakazu Matsumoto, Hideki Tanaka

JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 81 ( SUPPL. A ) 2012年9月

担当区分：筆頭著者,　責任著者記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：PHYSICAL SOC JAPAN

We show a relevant metastable phase diagram of the polymorphs of the Frank-Kasper type clathrate hydrate by estimating the chemical potential of the second most stable phase as well as the most stable one at given thermodynamic conditions with arbitrarily chosen guest molecules.