Molecular Gas Flow LaboratoryAssociate Professor Shigeru Yonemura

Study of Gas Film Lubrication Appearing at the Micro/NanoscaleIt was reported that the coefficient of friction decreases drastically when a partly polished

diamond-coated surface slides on a rotating metallic disk. In this experiment, the sliding was

noiseless, which indicates that the sliding mechanism is the gas film lubrication, and the

diamond-coated surface is suspended in the air. In this study, we focused on and investigated the

micro/nanoscale gas flow between both surfaces, and clarified the floating mechanism of the

diamond-coated surface by performing numerical simulations and by theoretical consideration.

Results showed that the high gas pressure was generated by microasperities on the surface, and then

gas lubrication was achieved. This result indicates that if the fine structure on the surface is the same

with this simulation, then high gas pressure will be generated in the same way even if the surface

material is not diamond. This pressure generation becomes considerable when spacing between both

surfaces is reduced from microscale to nanoscale, and it disappears at macroscale. This gas

lubrication phenomenon appears only at the micro/nanoscale. Results of this study are expected to

spur development of a new gas lubrication system.

Fig. 1 Computational domain. Fig. 2 Pressure distribution

(u = 10 m/s, l1 = l2 = 11.52 μm, d = 1.44 μm)

Study of self-bias potential in the radio frequency magnetron plasmaRadio frequency (RF) magnetron discharge is widely used in fabrication processes, such as

sputtering, used for semiconductor devices. During sputtering, high-energy ions accelerated by an

electrical field hit the target and sputter atoms from the target. Those sputtered atoms are deposited

on the substrate, thereby producing a thin film. Ions cannot follow the RF electric field. They move

in accordance with the time-averaged electric field. Consequently, they are accelerated by the

potential difference between the time-averaged plasma potential and the self-bias potential appearing

on the target. The sputtering rate depends strongly on the energy of incident ions. Therefore, it is

important to elucidate the characteristics of the self-bias potential. Little is known about the self-bias

potential in RF magnetron discharge, although much knowledge related to self-bias potential in RF

capacitively-coupled plasmas without magnetic fields has been obtained experimentally and

theoretically. This study clarified the discharge structure and characteristics of the self-bias potential

in the RF magnetron discharge.

Study of microplasmaPlasma-enhanced chemical vapor deposition (PECVD) is used to fabricate thin films, which are

necessary to produce electronic devices such as liquid-crystal displays and solar cells. Along with

the recent miniaturization of devices, as seen in μ-TAS or MEMS, microplasma technology is

attracting attention. This study examined the SiH4 microplasma structure, as generated by DC

electrodes arranged on both ends of the glass tube, by performing self-consistent PIC/MC

simulations. Strong interaction was observed between the tube wall and the plasma bulk.

Most electrons were generated near the sheath edge along the tube surface. This structure

differs greatly from that of a traditional plasma reactor. Results show that the electron number

density becomes higher and the discharge starting voltage decreases when the tube radius is reduced

from 1.5 mm to 0.5 mm. We clarified the mechanisms of these phenomena theoretically.

Relevant journal papers

S. Yonemura and K. Nanbu, DC Self-bias Voltages in Radio Frequency Magnetron

Discharges, Thin Solid Films, Vol. 506-507, pp. 517-521 (2006).

L. Tong, S. Yonemura, H. Takana and H. Nishiyama, Effect of Configuration on

Microdischarge Structure in a Narrow Channel, Physics Letters A, Vol. 371, Issues 1-2, pp.

140-144 (2007).

S. Yonemura, M. Yamaguchi, T. Takeno, H. Miki and Toshiyuki Takagi, Effect of Micro Gas

Flow on Low Friction Properties of Diamond Coating with Partly Polished Surface, AIP

Conference Proceedings, Vol. 1084, pp. 1153-1157 (2008).

Related research budget

Grant-in-Aid for Young Scientists (B) (2005–2007), ¥2,500,000.

Grant-in-Aid for Scientific Research (C) (2008–2010), ¥4,550,000.

Grant-in-Aid for Scientific Research (C) (2011–2013), ¥5,330,000.

Molecular Heat Transfer LaboratoryProfessor Taku Ohara, Senior Assistant Professor (2011.4-)/Assistant Professor (2007.4–2011.3)/

Research Associate (2007.1–2007.4) Gota Kikugawa

Molecular Dynamics Mechanism Governing Thermal Transport Characteristics of Polymer Liquids and Soft Matter

Elucidation of molecular dynamics (MD) mechanisms that govern thermal energy transport in liquids gives an essential answer to the question of why the liquid exhibits this thermal conductivity. It also gives the required feature of molecules that exhibit desired properties, which leads to the design of thermal transport phenomena and the thermal media. In this study, contributions of inter- and intramolecular energy transfer to thermal energy transport in saturated liquid alkanes were evaluated quantitatively based on a newly derived MD expression of heat conduction flux. The results showed that the contribution of intramolecular energy transfer increases as the molecular chain length increases, and is a dominant factor at a molecular weight of several hundreds. These findings suggest that a peculiar anisotropic heat conduction occurs in soft matter formed by self-organization of polymer molecules with a certain orientation. This was demonstrated by a MD simulation of lipid membrane in water. It was found that the cross-membrane thermal conductivity is five times higher than the in-plane one.

Transport Properties at the Interface of Self-Assembled MonolayersSelf-assembled monolayer (SAM) and other organic thin materials are being studied extensively

as novel surface-modification techniques. An essential understanding of heat and mass transportproperties over such interfaces is of critical importance in various applications to nano- and

(a) (b)

Fig. 2 A snapshot of the alkanethiolate SAM and water solvent interface obtained from the molecular dynamics simulation. Figures (a) and (b) represent the methyl-terminated SAM (hydrophobic surface) and hydroxyl-terminated SAM (hydrophilic), respectively.

(a)

(b)

Fig. 1(a) Contribution of intramolecular energy transfer to heat conduction flux as a response to molecular chain length of liquid alkanes. (b) Lipid bilayer membrane formed by self-organization of chain lipid molecules.

biotechnologies. In this study, we performed molecular dynamics simulations of typical SAM interfaces with various solvents in order to investigate heat transfer characteristics in detail. As a result, it was found that the SAM modification enables a decrease of thermal resistance at the organic solvent–gold interface. Moreover, we discussed the effect of an affinity between SAM and solvent on thermal boundary resistance and the microscopic mechanisms of peculiar heat transfer inside the SAM layer, which has a highly ordered molecular orientation.

Mass Transport Characteristics in the Vicinity of Solid-Liquid InterfacesAdsorption and desorption of solute and

solvent molecules to/from a solid-liquid interface, which are influenced by the liquid structure in the interface region and mass transport characteristics, are governing factors in the processes of chemical treatment of nanostructures and dynamic coating. In this study, the processes of surface treatment of SiO2 and alcohol substitution of water are simulated by MD and the free energy distribution for transport of molecular species is measured. Based on these results, mass transport characteristics in liquids in the vicinity of solid surfacesand influences of molecular-scale structure in the liquids are analyzed.

Relevant journal papersD. Torii, T. Ohara and K. Ishida, Molecular scale mechanism of thermal resistance at solid-liquid interfaces (Influence of interaction parameters between solid and liquid molecules), Transactionsof ASME, Journal of Heat Transfer, Vol. 132, 012402 (2010).

T. Nakano, G. Kikugawa and T. Ohara, A molecular dynamics study on heat conduction characteristics in DPPC lipid bilayer, Journal of Chemical Physics, Vol. 133, 154705 (2010).

T. Ohara, Tan C.-Y., D. Torii, G. Kikugawa and N. Kosugi, Heat conduction in chain polymer liquids: Molecular dynamics study on the contributions of inter- and intramolecular energy transfer, Journal of Chemical Physics, Vol. 135, 034507 (2011).

Relevant research budgetsGrant-in-Aid for Scientific Research (C) (2006–2008), ¥3,500,000Grant-in-Aid for Scientific Research (C) (2009–2011), ¥4,680,000, and others

AwardsJSME Young Engineers Awards, Gota Kikugawa (2009.4.7)JSME Medal for Outstanding Paper, Taku Ohara (2009.4.7)JSME Thermal Eng. Division Awards for Outstanding Achievement, Taku Ohara (2011.3.31）Japan Society of Thermophysical Properties Best Paper Awards, Taku Ohara and Gota Kikugawa(2011.11.22)

(a)

(b)

Fig. 3(a) Measurement of free energy by the analysis of IPA molecules immersed at a SiO2(011)-water interface. (b) Substitution of water by IPA in the vicinity of a SiO2 surface.

Nanoscale Interfacial Flow LaboratoryAssociate Professor Takashi Tokumasu

Development of Next Generation Fuel Cell System by Large-scale Molecular Dynamics Simulations

We analyze the transport phenomena of reactant materials in a polymer electrolyte fuel cell (PEFC) using large scale molecular dynamics simulations with a supercomputer to develop materials or systems in which the reactant materials can transport efficiently. Proton, oxygen and water, as the reactant materials, must be transferred to electrode catalysts efficiently to improve the PEFC efficiency. These materials, however, transfer through flow fields of which the size is of the order of nanometer or micrometer. Therefore the flow characteristics cannot be obtained throughconventional continuum theory. In this study, we simulate the nanoscale transport phenomena in fuel cells by molecular dynamics and obtain the key factor to ascertain the characteristics of these transport phenomena to construct the design concept of a new system or material that has a structure suitable for the transport property of these reactant materials. The research is collaborative withvarious companies or research institutes. We play our role in helping Japan to establish the technology of this field earliest in the world.

0.04 0.06 0.08 0.10 0.12 0.14

0.0

0.2

0.4

0.6

0.8

1.0

Initial Translational Energy

DissociationProbability[-]

: Pt-Fix: T=0 K: T=300 K

Dissociation phenomena of H2 on Pt catalystOxygen permeability of ionomerin Catalyst Layer

Phase diagram of water in a nano pore of MPL(collaborative research)

Transport properties of nanoscale water droplet in MPL

Proton diffusivity in PEM

Relativeenergy(kcal/mol)

q (Å)

0 1 2 3 4 50

3

6

9

12

15

MSD of H3O+

Time [ps]

MSD[?

2]

Fig. 1. Large-scale molecular dynamics simulations of transport phenomena of materials

through the parts of PEFC.

Development of Simulation Method Considering the Quantum Effect of MoleculesMolecules have quantum effects to a greater or lesser degree. In many cases, the effects

strongly influence flow fields. Regarding the transport phenomena of proton, which determines the

efficiency of fuel cells, for instance, the Grotthus mechanism, in which dissociation and

recombination occurs between a proton and water

molecule, determines the transport ability. Regarding the

thermodynamic properties of liquid hydrogen, the

uncertainty of position of molecule becomes remarkable

because of the light mass of hydrogen atom, and the

phenomenon affects the pressure of liquid hydrogen.

This study was conducted to reproduce real flow

properties by molecular dynamics simulations and to

analyze the influence of the quantum effect on the flow

properties by including quantum effects of molecules in

molecular dynamics simulations.

Relevant journal papers

T. Tokumasu, D. Ito, The Dynamic Effects of Dissociation Probability of H2-Pt(111) System by

Embedded Atom Method, Journal of Applied Physics, Vol. 109, 063509 (2011).

T. Tokumasu, I. Ogawa, M. Koyama, T. Ishimoto, A. Miyamoto, A DFT Study of Bond

Dissociation Trends of Perfluorosulfonic Acid Membrane, Journal of Electrochemical Society,

Vol. 158, B175-B179 (2011).

T. Tokumasu, M.-H. Meurisse, N. Fillot, P. Vergne, A Molecular Dynamics Study of a

Nanoscale Liquid Bridge under Shear, Tribology International, accepted (2012).

Related research budgets

Grant-in-Aid for Scientific Research (B) (2012–2014), ¥19,282,000

New Energy and Industrial Technology Development Organization (NEDO), Strategic

Development of PEFC Technologies for Practical Application, ¥70,161,000

Awards

Japan Electrochemistry Poster Award, Takashi Tokumasu et al. (2008, 3, 30)

Fig. 2. Schematic diagram of liquid

hydrogen by centroid molecular

dynamics simulation.

Biological Nanoscale Reactive Flow LaboratoryProfessor Takehiko Sato

Activation and Inactivation Mechanisms of Cell Viability by Plasma Flow at Atmospheric Pressure

We aim at clarifying the effects of chemical species generated by a plasma flow on cell

viability for the fundamental study and the application of plasma medicine. We have clarified that

hydrogen peroxide among stable chemical species generated by the plasma flow is the main factor

for inactivation of cell viability by analyzing cell survival ratio, morphological observation (Fig. 1),

reactive oxygen species generation in the cells, effects of catalase on cell survival ratio and

comprehensive gene analysis (Fig. 2).

Sterilization and Chemical Transport Mechanisms by Plasma Flow at Atmospheric Pressure

To reduce infection risks posed by new strains of influenza, by nosocomial infection, and so on,

we aim at developing a plasma sterilization device and clarifying the sterilization mechanism. We

have clarified the radical transport in the plasma flow (Fig. 3) by the fluid engineering point and

damage such as potassium leakage and deformation of the E. coli to elucidate sterilization

mechanisms.

Fig. 1. Morphological observation of HeLa cells for the untreated case (a) and the plasma treated case (b).

Fig. 3 Visualization of the plasma flow (a) and emission distribution of the excited N2.

Fig.4 SEM images of E. coli for the untreated case (a) and plasma-treated case (b).

Fig. 2. Scatter plot of the gene expression intensities obtained by the comprehensive gene analysis for the plasma-treated and H2O2-added cases.

Thermal flow Field Analysis of a Gas–Liquid Plasma Flow and Functional Enhancement of Water

To apply medical applications and environmental treatment, we have clarified the thermal flow

field of an atmospheric plasma flow on water because a gas–liquid system is a typical case in many

applications. The gas flow (Fig. 5) and water flow were induced by the plasma. The flow is the main

factor of the chemical transport. We also obtained that oxygen–reduction potential (ORP) decreased

to -150 mV, which is high reduction property by plasma in water.

Fig. 5. Induced gas flow between the electrode and water surface in the air by the plasma flow.

Relevant journal papers

T. Sato, T. Miyahara, A. Doi, S. Ochiai, T. Urayama, T. Nakatani, Sterilization Mechanism for

Escherichia coli by Plasma Flow at Atmospheric Pressure, Applied Physics Letters, Vol. 89,

073902 (2006).

T. Sato, S. Ochiai, T. Urayama, Generation and Transport Mechanisms of Chemical Species by

a Post-Discharge Flow for Inactivation of Bacteria, New Journal of Physics, Vol. 11, 115018

(2009).

T. Sato, M. Yokoyama, K. Johkura, A key inactivation factor of HeLa cell viability by a plasma

flow, Journal of Physics D: Applied Physics, Vol. 44, 372001 (2011).

Related research budgets

Grant-in-Aid for Scientific Research (A) (2009–2011), ¥36,200,000

Grant-in-Aid for Scientific Research (B) (2007–2008), ¥15,600,000

Awards

JSME, Environmental Engineering Division, Research Achievement Award, Professor Takehiko

Sato (2011.6.30)

Patent No. 4902842, “Plasma Generation Method and Plasma Generation Device”, Takehiko Sato

et al. (registered on Jan. 13, 2012)

Complex Flow Systems LaboratoryAssistant Professor Yuka Iga

Professor (–2012.3) Toshiaki Ikohagi

Numerical Analysis of High-speed Droplet ImpactThe soundness of high-speed gas–liquid two-phase fluid systems is sometimes threatened by

flow phenomena. For instance, in a high-pressure vapor flow in a secondary condenser pipe installed at nuclear reactors, erosion of the pipe wall results from high-speed liquid droplets impacting on the wall. In this study, three-dimensional two-phase fluid / solid coupling numerical simulation areperformed for the liquid droplet impact. By introducing a new estimation index which is the elastic impact region, a power index of the relation between erosion volume and the droplet diameter or the impact speed is indicated. The power index of the relation agrees with the existing experimental equitation of erosion prediction. Additionally, the attenuating effect of a thin liquid film on a wall isindicated numerically, in which the maximum pressure and maximum equivalent stress decrease exponentially with increasing liquid film depth.

This study is linked directly to countermeasures against aging degradation of atomic power plants. The results are expected to contribute to the development of fluid system safety evaluation.

(a) Flat solid surface (b) Thin water film surface (c) Wedged surfaceFig. 1. Aspects of pressure-wave and stress-wave propagation in high-speed droplet impact on solid

surfaces of several types.

Development of Numerical Prediction Method of Cavitation ErosionIn high-speed liquid flow, erosion sometimes results from a cavitation bubble collapse.

Development of A numerical prediction method is anticipated. In this study, coupling numerical calculation is performed for homogeneous cavitating flow simulation around a hydrofoil, tracking simulation of spherical bubble in the cavitating flow, and simulation of a non-spherical bubble collapse near a wall, with consideration of the number density distribution of bubbles in an actual flow field. Then, the erosion rate can be predicted quantitatively using numerical simulation. Results show that the predicted erosion rate agrees well with the experimentally obtained value.

Fig. 2. Time evolution of the aspect of collapse and rebound of single bubble near a wall.

Cavitation Instabilities in Liquid Propellant Rocket TurbopumpIn a liquid-propellant rocket turbopump, cavitation instabilities sometimes occur, which

threaten the soundness. That suppression process increases the cost of the liquid rocket launch. The turbopump is ultra-high-speed and high-pressure fluid machinery. Clarification of the cavitation instabilities is not so easy to investigate solely through experimentation. In this laboratory, through collaboration between experiments performed at the JAXA Kakuda Space Center and supercomputing in IFS, the cavitation instabilities are investigated. In supercomputing, a three-blade inducer in the turbopump inlet is simulated using a three-blade cyclic cascade. The occurrence mechanism of a rotating cavitation, the propagation mechanism of pulsation in cavitation surge, and influence of acceleration during the launch on the cavitation instabilities were clarified and a control technique of the instabilities by tandem cascade was developed.

Fig. 3. Super-synchronous rotating cavitation arising in three-blade cyclic flat-plate cascade.

Relevant journal papers H. Sasaki, Y. Iga, T. Ikohagi, Study of Droplet Impingement Phenomena by Fluid/Solid Coupled

Simulation, Proc. Joint International Conference on Supercomputing in Nuclear Applications and Monte Carlo 2010/SNA+MC2010, Tokyo JAPAN (2010), No. 10189.

N. Ochiai, Y. Iga, M. Nohmi, T. Ikohagi, Numerical Analysis of Nonspherical Bubble Collapse Behavior and Induced Impulsive Pressure during First and Second Collapses near the Wall Boundary, Journal of Fluid Science and Technology, Vol. 6, 860-874 (2011).

Y. Iga, Y. Yoshida, Mechanism of Propagation Direction of Rotating Cavitations in a Cascade, Journal of Propulsion and Power, Vol. 27, 675-683 (2011).

Related research budgetsIntelligent Cosmos Research Institute, ”Structural Improvement of the stronger measures for aging degradation of atomic power plants” (2006–2010), ¥49,329,000Ebara Corporation, “Technique of cavitation analysis with considering of application to prediction of performance and erosion in fluid machineries” (2009–2011), ¥1,985,000

AwardsJSME Encouraging Prize (Research), Yuka IGA (2006. 4. 7)

JSME Fluid Ergineering Division Prize, Toshiaki Ikohagi(2008.10)

Advanced Computational Fluid Dynamics LaboratoryProfessor Yuji Hattori, Assistant Professor Wakana Nakano

Professor (–2009.3) Osamu Inoue, Assistant Professor (–2006.9) Nozomu Hatakeyama

Development of High-Precision Numerical Methods for Simulation of Flow in Complex and/or Deforming Geometries

Increasing needs are being expressed for highly accurate simulation of flows in complex

geometry and flows which involve moving and/or deforming bodies. We are developing numerical

methods for these flows by application of the volume penalization (VP) method, which is one of the

immersed boundary methods. First, by basic studies of a simple one-dimensional problem, we have

developed a new method for improving the accuracy of the VP method. Next, the method is applied

to simulate the formation of a vortex pair by piston motion and the evolution of localized

disturbances in the elliptic flow. Finally, the accuracy of the VP method for compressible flow is

investigated. The aeroacoustic sound generated from the flow past a square cylinder is simulated by

VP method and the sound is captured with sufficient precision, showing that the method is useful for

direct numerical simulation of aeroacoustic sound in complex and/or deforming geometries.

Fig. 1. Formation of a vortex pair simulated by VP method. Fig. 2. Sound generation simulated by VP method.

Statistical Properties of TurbulenceThe statistical properties of turbulence are not only a long-standing problem of physics but also

the key to establishing reliable turbulence models required for simulation of high-Reynolds number

flows encountered in engineering. We are studying the statistical properties of turbulence mainly by

direct numerical simulations. The dynamics of high-enstrophy regions in the three-dimensional

incompressible turbulence including advection/deformation, creation/extinction and merging/fission

is studied by DNS and interactive three-dimensional visualization. For two-dimensional

compressible turbulence, the scaling of the density spectrum is shown to depend on the initial

condition for entropy; when entropy is non-uniform sheet structures are found to emerge in the

density field.

Fig. 3. Vortical structures in 3D turbulence. Fig. 4. Sheet structures in compressible turbulence.

Vortex DynamicsIt is important to understand vortex dynamics when investigating and understanding flow

phenomena. The fundamental properties and the dynamics of various vortical structures are studied.The curvature instability, which appears when vortex tubes are curved, is studied for vortex rings and helical vortices; the effects of curvature, torsion, rotation and axial flow as well as their combined effects are clarified using theoretical analysis. Evolution of localized disturbances in the elliptical flow is studied using DNS. The process starting from an infinitesimal disturbance andleading to turbulence is clarified in detail. The results suggest an effective method for destabilizingvortices.

Fig. 5. Growth rates of curvature instability. Fig. 6. Localized disturbance in the elliptical flow.

Relevant journal papers Y. Hattori, Y. Fukumoto, Short-Wavelength Stability Analysis of a Helical Vortex Tube, Physics

of Fluids, Vol. 21, 014104 (2009). Y. Hattori, Y. Fukumoto, Short-wave Stability of a Helical Vortex Tube: The Effect of Torsion

on the Curvature, Theoretical and Computational Fluid Design, Vol. 24, 363-368 (2010). Y. Hattori, K. Hijiya, Short-wavelength stability analysis of Hill's vortex with/without swirl,

Physics of Fluids, Vol. 22, 074104 (2010).

Related research budgetsGrant-in-Aid for Scientific Research (B) (2007–2008), ¥8,970,000Grant-in-Aid for Scientific Research (C) (2008–2011), ¥3,000,000

Injection well

CO2 leakage path(Fracture)

805010851

0.50.1

0.001

Porous layer filled with reaction grout

Large-Scale Environmental Fluid Dynamics LaboratoryProfessor Takatoshi Ito, Assistant Professor Hiroyuki Shimizu

In-situ Reaction Method to Remedy Leakage from Geological CO2 Storage Reservoirs In order to remedy leakage from a CO2

storage reservoir through pre-existing and/or

induced fractures, we have proposed a new

concept to use an aqueous solution. When the

solution encounters dissolved CO2, precipitation

will occur due to chemical reaction. As a result,

the permeability will be reduced by filling the

pores and fractures in the rocks with the

precipitates. We verified this idea through

laboratory experiments and numerical

simulations.

Estimation of Pressure and Flow Distribution in Fractured Geothermal Reservoirs at Few km Deep Using Microseismic Signals

Geothermal energy development depends

upon how well water flow is understood. In

response to such requirement, we have

developed a method to use a microseismic (MS)

signal as a measure of pressure at its hypocenter,

where the MS are caused by fluid injection. By

compiling the estimated local pressure in a

manner, we can estimate pressure propagation

during fluid injection. From the estimated

pressure propagation, we can estimate

distributions of flow-pathways and hydraulic

conductivity along them.

Fig. 1. Formation of impermeable barrier to

stop leakage through a fracture.

Fig. 2. Estimated pressure distribution

(Australian test site, 4 km depth)

1cm SH

SH

Sh

Sh

Casing pipeSlit

Study of Hydraulically-induced Fracture Behavior in Unconsolidated Sands for Methane Hydrate (MH) Development

For production of gas from MH, the MH

should be dissociated within the layers for the

resultant gas to be collected through wells and

production systems. The dissociation will be

driven by decreasing pressure of the layers.

Hydraulic fracturing may contribute to enhance

gas production. However, the technique of

hydraulic fracturing was originally developed

assuming cohesive rocks but not incohesive

ones such as unconsolidated sediments below

seafloor in which MH is contained. Thus we

have carried out laboratory fracturing tests and

as a result we have found a significant difference

between the fracture behaviors in incohesive and

cohesive rocks.

Relevant journal papers

H. Shimizu, M. Murata, T. Ishida, The Distinct Element Analysis for hydraulic fracturing in

hard Rock considering fluid viscosity and particle size distribution, International Journal of

Rock Mechanics and Mining Sciences, Vol. 48, 712-727 (2011).

T. Ito, K. Yamamoto, S. Nagakubo, Effect of anisotropic confining stresses on

hydraulically-induced fracture, Proceedings of the 45th US Rock Mechanics / Geomechanics

Symposium, San Francisco, ARMA 11-247 (2011).

T. Ito, T. Shono, K. Sekine, K. Yamamoto, A new laboratory test for shear fracture formation

and its permeability measurement, Proceedings of the 12th ISRM International Congress on

Rock Mechanics, Beijing, Vol.1, No.1, pp.645-648 (2011).

Relevant research budgets

Grant-in-Aid for Scientific Research (B), Takatoshi Ito（2009～2011），¥14,950,000

Research fund of JOGMEC, Takatoshi Ito（2010～2011），¥4,250,000

Awards

JCRM Medal for Outstanding Paper, Hiroyuki Shimizu (2011.6.9)

Fig. 3. Fracture induced by laboratory test.

It is branched unlike cohesive rock.

Theoretical Fluid Dynamics LaboratoryConcurrent Professor Michio Tokuyama, Assistant Professor Yayoi Terada

Slow Dynamics near the Glass Transition－Lateral diffusion of magnetic colloidal chains and monolayer colloids –

Liquid becomes glass through the supercooled liquid state if it is cooled with avoidance of

crystallization. Recently, novel glasses such as colloidal glasses, bulk metallic glasses, and so on

have been developed. Their unique properties receive considerable attention. However, the

mechanism of glass transition remains unclear. In our laboratory, we study the dynamics near the

glass transition by performing computer simulations.

Magnetic colloidal chains confined with thin films and monolayer magnetic colloids are good

examples of glass formers. When dilute suspensions of magnetic colloidal particles are confined in

thin films and a strong external field is applied perpendicular to the films, magnetic colloidal

particles dispersed in a solvent form colloidal chains parallel to the field and the lateral diffusion of

the chains can be observed. These diffusive motions of the colloidal chains and monolayer colloids

slow and ultimately become a glass state when the external magnetic field is increased.

Universalities in the dynamics of chains and monolayer colloids in fluid phase are explored based on

the mean-field theory recently proposed by Tokuyama. The long-time self-diffusion coefficient of a

chain is shown to obey a singular function of a control parameter proportional to the square of the

applied field strength, even though the size polydispersity of colloids is changed in Fig. 1.

Slow Dynamics of Hard-sphere Fluids and Hard-disk Fluid near the Glass TransitionThe glass transition can be observed on two-dimensional and three-dimensional systems. The

long-time diffusion process of hard spheres is compared with that of hard disks by performing

extensive molecular simulations with changing of the volume fraction. The long-time self-diffusion

coefficient of both hard disks and hard spheres is described by the singular function proposed

theoretically by Tokuyama. The characteristic times of the β relaxation process and the α relaxation

process of hard disks are also found to be similar to those of hard spheres when the particles had the

same long-time self-diffusion coefficient. The spatial dimension changes the value of the glass

transition point and peak height of the non-Gaussian parameter which are related to the geometric

packing characteristics of hard disks and hard spheres.

Relevant journal papers

Y. Terada, M. Tokuyama, Universalities in the dynamics of suspensions of magnetic colloidal

chains confined in thin films, Journal of the Physical Society of Japan, Vol. 78, 084803 (2009).

Y. Terada, M. Tokuyama, Lateral diffusion of magnetic colloidal chains confined in thin films

and monolayer colloids, Journal of the Physical Society of Japan, Vol. 79, 034802 (2010).

Y. Terada, M. Tokuyama, Spatial Dimensionality Dependence of Long-Time Diffusion on Two-

and Three-Dimensional Systems near Glass Transition, Intermetallics, Vol. 18, 1834-1836

(2010).

Related research budgets

Grant-in-Aid for Scientific Research (C) (2011–2013), ¥5,300,000

Awards

Best Poster Award for the 12th International Conference on Magnetic Fluids, Yayoi Terada

(2010.8.5)

Fig. 1. Snapshot of magnetic colloidal

monolayer and control parameter

dependence of long-time self-diffusion

coefficients of colloidal chains.

Fig. 2. Long-time self-diffusion coefficient

dependence of characteristic times of hard spheres

and hard disks: ◇ , mean free time (tf); □ ○,characteristic times related with β-relaxation (tγ, tβ);

△▽, characteristic times related with α relaxation

(tα, tα2); ◊ , characteristic time with long time

self-diffusion process (tDSL). Open symbols, hard

spheres; filled symbols, hard disks.