研究者詳細 - 松本　正和

On the Thermodynamic Stability of Clathrate Hydrates VI: Complete Phase Diagram 査読

Tanaka Hideki, Yagasaki Takuma, Matsumoto Masakazu

The Journal of Physical Chemistry B 122 ( 1 ) 297 - 308 2018年

Adsorption of Kinetic Hydrate Inhibitors on Growing Surfaces: A Molecular Dynamics Study 査読

Yagasaki Takuma, Matsumoto Masakazu, Tanaka Hideki

The Journal of Physical Chemistry B 122 ( 13 ) 3396 - 3406 2018年

Phase Diagram of TIP4P/2005 Water at High Pressure 査読

Masanori Hirata, Takuma Yagasaki, Masakazu Matsumoto, Hideki Tanaka

Langmuir 33 ( 42 ) 11561 - 11569 2017年10月

Communication: Hypothetical ultralow-density ice polymorphs 査読

Takahiro Matsui, Masanori Hirata, Takuma Yagasaki, Masakazu Matsumoto, Hideki Tanaka

JOURNAL OF CHEMICAL PHYSICS 147 ( 9 ) 091101 - 091101 2017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：AMER INST PHYSICS

More than 300 kinds of porous ice structures derived from zeolite frameworks and space fullerenes are examined using classical molecular dynamics simulations. It is found that a hypothetical zeolitic ice phase is less dense and more stable than the sparse ice structures reported by Huang et al. [Chem. Phys. Lett. 671, 186 (2017)]. In association with the zeolitic ice structure, even less dense structures, "aeroices," are proposed. It is found that aeroices are the most stable solid phases of water near the absolute zero temperature under negative pressure. (C) 2017 Author(s).

DOI： 10.1063/1.4994757

Formation of Clathrate Hydrates of Water-Soluble Guest Molecules 査読

Takuma Yagasaki, Masakazu Matsumoto, Hideki Tanaka

JOURNAL OF PHYSICAL CHEMISTRY C 120 ( 38 ) 21512 - 21521 2016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：AMER CHEMICAL SOC

Clathrate hydrates of water-soluble guest molecules, such as ethylene oxide (EO) and tetrahydrofuran (THF); have been often investigated in experimental studies instead of gas hydrates because their dissociation temperatures are higher than the ice point under ambient pressure. We examine the formation mechanism of EO and THF hydrates using molecular dynamics simulations. The crystal growth rates are determined by the simulations of the hydrate/solution two-phase coexistence. It is found that the growth rate of EO hydrate is an order of magnitude higher than that of THF hydrate. The growth rates of THF hydrate largely deviate from the Wilson-Frenkel model, while the model well approximates the growth rates of EO hydrate, indicating that trapping of guest molecules on the hydrate surface, which causes the slowing of crystal growth of THF hydrate, is insignificant for EO hydrate. We also perform long-time simulations of aqueous EO and THF solutions to examine nucleation of clathrate hydrate. Spontaneous nucleation occurs only in the EO solution within the simulation time. Similar to previous studies on methane hydrate, the obtained solid structure exhibits no long-range order. It is found that the 5(12) hydrate cage, which is the most dominant cage type in the early stage of the nucleation of methane hydrate, is not a major cage type in the nucleation process of EO hydrate.

DOI： 10.1021/acs.jpcc.6b06498

Thermodynamic Stability of Ice II and Its Hydrogen-Disordered Counterpart: Role of Zero-Point Energy 査読

Tatsuya Nakamura, Masakazu Matsumoto, Takuma Yagasaki, Hideki Tanaka

JOURNAL OF PHYSICAL CHEMISTRY B 120 ( 8 ) 1843 - 1848 2016年3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 why no hydrogen-disordered form of ice II has been found in nature despite the fact that most of hydrogen-ordered ices have hydrogen-disordered counterparts. The thermodynamic stability of a set of hydrogen-ordered ice II variants relative to ice II is evaluated theoretically. It is found that ice II is more stable than the disordered variants so generated as to satisfy the simple ice rule due to the lower zero point energy as well as the pair interaction energy. The residual entropy of the disordered ice II phase gradually compensates the unfavorable free energy with increasing temperature. The crossover, however, occurs at a high temperature well above the melting point of ice III. Consequently, the hydrogen-disordered phase does not exist in nature. The thermodynamic stability of partially hydrogen-disordered ices is also scrutinized by examining the free-energy components of several variants obtained by systematic inversion of OH directions in ice II. The potential energy of one variant is lower than that of the ice II structure, but its Gibbs free energy is slightly higher than that of ice II due to the zero-point energy. The slight difference in the thermodynamic stability leaves the possibility of the partial hydrogen-disorder in real ice II.

DOI： 10.1021/acs.jpcb.5b09544

Mechanism of Slow Crystal Growth of Tetrahydrofuran Clathrate Hydrate 査読

その他リンク： http://orcid.org/0000-0002-6799-6813

Takuma Yagasaki, Masakazu Matsumoto, Hideki Tanaka

JOURNAL OF PHYSICAL CHEMISTRY C 120 ( 6 ) 3305 - 3313 2016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

Tetrahydrofuran (THF) clathrate hydrate has been frequently used in experimental studies instead of gas hydrates because it forms at a temperature higher than the ice point under ambient pressure. In this paper, we compare the crystal growth rates of THF hydrate and ice using molecular dynamics simulations. It is demonstrated that the crystal growth of THF hydrate is much slower than that of ice. The growth rates of THF hydrate significantly deviate from a standard kinetic model known as the Wilson-Frenkel model, whereas it reproduces, the temperature dependence of the growth rate of ice. The slow crystal growth and the deviation from the Wilson-Frenkel model are attributed to the trapping of THF molecules in open small cages at the hydrate surface. We calculate the free energy profile of a THF molecule transferring from the bulk solution phase to the hydrate surface using the umbrella sampling technique. It is shown that a THF molecule trapped in an open small cage needs to cross one or two free energy barriers to escape from the surface region. We also refer to the similarity between the mechanism of slow growth of THF hydrate and the effect of kinetic hydrate inhibitors.

DOI： 10.1021/acs.jpcc.5b10293

Anomalous thermodynamic properties of ice XVI and metastable hydrates 査読

その他リンク： http://orcid.org/0000-0002-6799-6813

Takuma Yagasaki, Masakazu Matsumoto, Hideki Tanaka

PHYSICAL REVIEW B 93 ( 5 ) 2016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

A new ice polymorph, called ice XVI, has recently been discovered experimentally by extracting the guest molecules from Ne hydrate. The ice and its filled form (clathrate hydrate) have a unique network topology which results in several interesting properties. Here we provide a theoretical method to calculate thermodynamic properties of a semiopen system in equilibrium with guest gas and thus occupancy of the guest can be varied with temperature and pressure. Experimental observations such as the disappearance of negative thermal expansivity and contraction of the host lattice upon encaging guest molecules are well reproduced, and those behaviors are elucidated in terms of the free energy of cage occupation and its temperature and pressure dependence. We propose an application of the method for preparing ice XVI to create metastable clathrate hydrates having intriguing properties with much lower occupancy of guest molecules than that at equilibrium, which otherwise cannot form.

DOI： 10.1103/PhysRevB.93.054118

その他リンク： http://orcid.org/0000-0002-6799-6813

Chiral Ordering in Supercooled Liquid Water and Amorphous Ice 査読

Masakazu Matsumoto, Takuma Yagasaki, Hideki Tanaka

PHYSICAL REVIEW LETTERS 115 ( 19 ) 2015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 PHYSICAL SOC

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.

DOI： 10.1103/PhysRevLett.115.197801

Adsorption Mechanism of Inhibitor and Guest Molecules on the Surface of Gas Hydrates 査読

その他リンク： http://orcid.org/0000-0002-6799-6813

Takuma Yagasaki, Masakazu Matsumoto, Hideki Tanaka

JOURNAL OF THE AMERICAN CHEMICAL SOCIETY 137 ( 37 ) 12079 - 12085 2015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：AMER CHEMICAL SOC

The adsorption of guest and kinetic inhibitor molecules on the surface of methane hydrate is investigated by using molecular dynamics simulations. We calculate the free energy profile for transferring a solute molecule from bulk water to the hydrate surface for various molecules. Spherical solutes with a diameter of similar to 0.5 nm are significantly stabilized at the hydrate surface, whereas smaller and larger solutes exhibit lower adsorption affinity than the solutes of intermediate size. The range of the attractive force is subnanoscale, implying that this force has no effect on the macroscopic mass transfer of guest molecules in crystal growth processes of gas hydrates. We also examine the adsorption mechanism of a kinetic hydrate inhibitor. It is found that a monomer of the kinetic hydrate inhibitor is strongly adsorbed on the hydrate surface. However, the hydrogen bonding between the amide group of the inhibitor and water molecules on the hydrate surface, which was believed to be the driving force for the adsorption, makes no contribution to the adsorption affinity. The preferential adsorption of both the kinetic inhibitor and the spherical molecules to the surface is mainly due to the entropic stabilization arising from the presence of cavities at the hydrate surface. The dependence of surface affinity on the size of adsorbed molecules is also explained by this mechanism.

DOI： 10.1021/jacs.5b07417