Annual Report for Research Work in the fiscal year 2006

Transcription

1 JST Basic Research Programs C R E S T (Core Research for Evolutional Science and Technology) Annual Report for Research Work in the fiscal year 2006 Research Area : High Performance Computing for Multi-scale and Multi-physics Phenomena Research Theme Multiscale Simulations for Softmatters Name of Research Director, Belonging and Title: Ryoichi Yamamoto, Graduate School of Engineering,, Associate Professor

2 1.Outline of Research Work Polymeric and colloidal systems are important softmatter materials both from scientific and engineering points of view. We aim to achieve efficient computer simulations of those systems by developing 1) multi-scale methods which enable us to perform consistent simulations of microscopic (atoms, molecules, etc), mesoscopic (density fields, interfaces, etc), and macroscopic (shapes of materials, production processes, etc) variables and 2) an integrated software for material and process simulations. We expect that our method will give great impact not only on softmatter community but also on other frontier fields of science and engineering. The newly developed software enables us to bridge between microscopic information of the materials and physical behavior of the macroscopic systems. It will help also to design materials and processes by means of computer simulations. In fiscal year 2006, we opened four core groups; 1) molecular dynamics group (Yasuoka), polymer group (Masubuchi), colloid group (Yamamoto), and macroscopic material group (Taniguchi). Several tentative simulations have been performed already, but the main program development will be started in fiscal year 2007.

3 2.Content of Research Work We opened four core groups; 1) molecular dynamics group (Yasuoka), polymer group (Masubuchi), colloid group (Yamamoto), and macroscopic material group (Taniguchi), and are planning to interlink different simulates which have already been developed by themselves. Research activities of those core groups in 2006 are listed below. 1) Molecular Dynamics Simulation Group: In order to develop the simulator of polymer and colloidal suspension we studied as follows: for the polymer simulator the dissipative particle dynamics (DPD) method was applied to study the spontaneous self-assembly process for threadlike micelles. The DPD method can treat the phenomena for the wide-scale time range and length scales such as the formation process of the threadlike micelles. And it may be applied to polymer system. A part of these results were presented at the domestic meeting. For the colloid simulator molecular dynamics simulation with the isotropic periodic sum (IPS) method, which was developed by Wu and Brooks, was applied. The IPS method defined a local region for each particle within the cutoff distance and described the remaining region as images of the local region statistically distributed in an isotropic and periodic way. It is different from the lattice sum method such as Ewald summation method which sum over discrete lattice images generated by periodic boundary conditions. They reported that the potential energy of IPS method was similar to that of Ewald summation for homogeneous system. However, it is unknown to be able to apply IPS method to estimate any thermodynamic and transport properties. We calculated the transport properties with IPS method. A part of these results were presented at the domestic meeting. 2) Polymer Simulation Group: Possible methodologies for combination between the polymer dynamics simulator and macroscopic flow simulators and microscopic atomistic molecular simulators were investigated. For the combination with macroscopic simulators prediction of warpage of injection-molded product for different molecular weight of polymers was examined by continuum calculations with rheological properties calculated by the polymer dynamics simulator. For the bridging between the polymer simulator and microscopic molecular simulators in atomistic descriptions, similarity of the network structures obtained by the primitive path extraction in the atomistic simulations and obtained by the polymer dynamics simulation was investigated and analyzed in detail. 3) Colloid Simulation Group: We aim to bridge between a mesoscopic simulator for colloidal systems and a

4 large-scale molecular dynamics simulator. We plan to develop a unique method based on standard statistical mechanics rather than simply dividing a total space into several subspaces with different levels of physical description. In fiscal year 2006, we modified our simulation code for particle dispersions [KAPSEL: to take into account the effect of Brownian motions of the particles. Figure 1 shows the velocity auto correlation function of electrically neutral spherical particles immersed in a Newtonian solvent. It follows an exponential decay derived from the Langevin eq. in early times, but tends to show the hydrodynamic long-time tail t -3/2 in late times. The present extension enables us to simulate several cases where coupling between hydrodynamic interaction and the thermal fluctuation becomes important. Fig.1 (Left) The normalized velocity autocorrelation function of Brownian particles at k B T = 1. The dotted curve shows an exponential decay derived from the Langevin eq. The dashed curve shows hydordynamic long-time tail t -3/2. (Right) A snapshot of Brownian particles. The colored arrows on a vertical plane represent the local velocity of the solvent. 4) Process Simulation and Platform Group: In order to predict behavior of soft matters such as polymers, liquid crystals and so forth by process simulations, it is quite important to know how to incorporate microscopic degrees of freedom (e.g., entanglement of polymer chains and/or orientation of liquid crystal molecules) of them to equations of macroscopic variables such a stress field. When we solve macroscopic equations, we need to use a constitutive equation that gives a relation between the stress field and velocity field. However, there is no general constitutive equation that is applicable to various soft matter systems. In addition, since in actual processes there are many cases that the systems are at non-equilibrium state, it becomes difficult to apply the constitutive equations to such process simulations. Therefore, in this study, we are addressing to incorporate a field obtained by a simulator dealing with a microscopic degree of freedom to a macroscopic simulation, instead of using a specific constitutive equation to obtain the field. Among others, we focus on process simulation of polymer melts and liquid crystal systems to achieve the approach mentioned above. In such systems, it is quite effective to use a coarse grained model as a microscopic model that can deal with orientation dynamics of liquid crystal molecules and can deal with entanglement dynamics of

5 polymer chains. By simultaneous coupling these microscopic simulations with a macroscopic flow simulation, we are planning to make a more precise flow prediction of polymeric and liquid crystal systems. Since this fiscal year is the first year of the present project, we addressed fundamental problems how to deal with the microscopic orientation dynamics of liquid crystal under a shear flow. With regards to the method to simulate orientation dynamics of liquid crystal system, there are two methods. One is to directly solve dynamics of each liquid crystal molecules using a Langevin type equation. Another is to solve a Fokker-Plank type equation for orientation distribution function of liquid crystal. Since the former method is computationally quite heavy, it is not applicable to the present problem. So we developed the simulator that can deal with the orientation dynamics of liquid crystal using a Fokker Plank type equation. In the next fiscal year using the simulator developed in this year and a new microscopic simulator for microscopic polymer dynamics, we will develop a simulation method for a macroscopic flow.

6 3.Formation of Research Work (1) Yamamoto Group (Department of Chemical Engineering, Graduate School of Engineering, ) Group Members: Name Affiliation Title Period Ryoichi Department of Chemical Associate 2006 Oct - Yamamoto Engineering, Graduate Professor School of Engineering, Kana Ishida Department of Chemical CREST 2006 Oct - Engineering, Graduate Office Staff School of Engineering, Takuya Iwashita Department of Chemical D Oct - Engineering, Graduate School of Engineering, Masanobu Department of Chemical M Oct - Hisaichi Engineering, Graduate School of Engineering, Items of Research: 1) Extension of Colloid Simulator 2) Bridging between Molecular Dynamics Simulator and Colloid Simulator 3) Bridging between Polymer Simulator and Colloid Simulator 4) Bridging between Process Simulator and Colloid Simulator 5) Development of a New Platform for Simulations of Softmatters 6) Direction of the Whole Project (2) Yasuoka Group (Department of Mechanical Engineering, Faculty of Engineering, Kyoto University) Group Members: Name Affiliation Title Period Kenji Yasuoka Department of Mechanical Engineering, Faculty of Associate Professor 2006 Oct - Engineering, Kyoto University Norimitsu Arai Department of Mechanical Engineering, Faculty of D Oct - Engineering, Kyoto University Items of Research:

7 1) Development of High Performance Molecular Dynamics Code for Polymer and Colloid Simulations. 2) Development of Coarse Grained Molecular Dynamics Simulation. 3) Bridging between Molecular Dynamics Simulator and Polymer Simulator 4) Bridging between Molecular Dynamics Simulator and Colloid Simulator 5) Development of a New Platform for Simulations of Softmatters (3) Masubuchi Group (Division of Multidisciplinary Chemistry, Institute for Chemical Research, ) Group Members: Name Affiliation Title Period Yuichi Masbuchi Division of Associate 2006 Oct - Multidisciplinary Professor Chemistry, Institute for Chemical Research, Items of Research: 1) Bridging between Molecular Dynamics Simulator and Polymer Simulator 2) Bridging between Polymer Simulator and Colloid Simulator 3) Bridging between Polymer Simulator and Process Simulator 4) Development of a New Platform for Simulations of Softmatters (4) Taniguchi Group (Department of Polymer Science and Engineering, Faculty of Engineering, Yamagata University) Group Members: Name Affiliation Title Period Takashi Taniguchi Department of Polymer Associate 2006 Oct - Science and Engineering, Professor Faculty of Engineering, Yamagata University Items of Research: 1) Bridging between Colloid Simulator and Process Simulator 2) Bridging between Polymer Simulator and Process Simulator 3) Development of a New Platform for Simulations of Softmatters 4.Publication of Research Results

8 (4-1) Publication of Thesis (The original Work) 1 Number of Publications ( 0 times-domestic, 0 times-international) 2 Detailed Information of Thesis (4-2) Patent Application 1 Cumulative Number 1) Patent Applications in the fiscal year 2006 (Domestic- 0 Cases, Oversea- 0 Cases) 2) Cumulative number of Patent Applications for the research period of CREST (Domestic- 0 Cases, Oversea- 0 Cases) 3) Details for this fiscal year