Mikio Yamanoi

Generalized mapping of multi-body dissipative particle dynamics onto fluid compressibility and the Flory-Huggins theory

In this work, a generalized relation between the fluid compressibility, the Flory-Huggins interaction parameter (χ), and the simulation parameters in multi-body dissipative particle dynamics (MDPD) is established. This required revisiting the MDPD equation of state previously reported in the literature and developing general relationships between the parameters used in the MDPD model. We derive a relationship to the Flory-Huggins χ parameter for incompressible fluids similar to the work previously done in dissipative particle dynamics by Groot and Warren. The accuracy of this relationship is evaluated using phase separation in small molecules and the solubility of polymers in dilute solvent solutions via monitoring the scaling of the radius of gyration (Rg) for different solvent qualities. Finally, the dynamics of the MDPD fluid is studied with respect to the diffusion coefficient and the zero shear viscosity.

The Lowe-Andersen thermostat as an alternative to the dissipative particle dynamics in the mesoscopic simulation of entangled polymers

Dissipative Particle Dynamics (DPD) has shown a great potential in studying the dynamics and rheological properties of soft matter; however, it is associated with deficiencies in describing the characteristics of entangled polymer melts. DPD deficiencies are usually correlated to the time integrating method and the unphysical bond crossings due to utilization of soft potentials. One shortcoming of DPD thermostat is the inability to produce real values of Schmidt number for fluids. In order to overcome this, an alternative Lowe-Anderson (LA) method, which successfully stabilizes the temperature, is used in the present work. Additionally, a segmental repulsive potential was introduced to avoid unphysical bond crossings. The performance of the method in simulating polymer systems is discussed by monitoring the static and dynamic characteristics of polymer chains and the results from the LA method are compared to standard DPD simulations. The performance of the model is evaluated on capturing the main shear flow properties of entangled polymer systems. Finally the linear and nonlinear viscoelastic properties of such systems are discussed.

Direct fibre simulation of carbon nanofibres suspensions in a Newtonian fluid under simple shear.

This work studies the effect of simple shear flows on the dispersion of carbon nanofibres (CNF) in a low viscosity Newtonian matrix. Analysis was performed by using a direct fibre simulation based on Particle Simulation Method (PSM) especially focusing on structure changes under shear flows. Suspensions of CNF/epoxy of different concentrations varying from 0.1 to 3.0 wt% were prepared by simple hand-mixing the as-received fibres with the epoxy resin. These suspensions were then subjected to different flow conditions (shear rates and strains) and their rheological behaviour was characterised. It is demonstrated that simulation can reproduce shear-thinning and structure developments induced by shear flow at different shear rates. Especially at low shear rates, flow induced helical bands were predicted by simulation, which was observed in experiments performed by other researchers and reported in the literature. From the results obtained it is concluded that the direct fibre simulator is a useful tool to design nano-scale fibre composites, allowing for optimisation of the critical parameters to determine the most adequate conditions leading to the required level of fibre dispersion.

Nano-precision combined process of electrolytic in-process dressing grinding and magnetic assisted polishing on optics glass material

Abstract This study is focused on the application of an effective fabrication method combining electrolytic in-process dressing(ELID) grinding and magnetic assisted polishing(MAP) to nano-precision mirror surface grinding on the optics glass-ceramic named Zerodure that is commonly used in precision optics components. The results show the variation of surface roughness after MAP processes utilizing Fe+CeO 2 , Fe+CeO 2 +diamond paste and Fe+diamond paste are applied to ELID ground surfaces. The MAP surface roughnesses for ELID ground surface roughnesses( R a ) of 52.1, 39.8 and 51.1 nm using #1200 grinding wheel are improved to 6.1, 4.6 and 1.9 nm, respectively. The surface roughness of MAP process using Fe+CeO 2 +diamond paste is superior to that using other processes. Moreover, it takes less than 10 min to conduct the MAP processes. The combined method suggested effectively reduces the working time to get the required surface qualities.

Direct Numerical Simulation of Carbon Nanofiber Composites in Simple Shear Flow

A coarse grained molecular dynamics simulator based on PSM (Particle Simulation Method), in which a fiber is modeled as connected spheres with stretch forces, bending torques and torsion torques, has been developed for analyzing structures of carbon nanotube (CNT) and carbon nanofiber (CNF) composites and their related rheological properties under simple flow fields, such as shear flow and extensional flows. The software takes into account fiber flexibility, hydrodynamic interactions and van der Waals interactions, without Brownian motion. It can predict aggregated structures under simple shear flows qualitatively, which were obtained in CNT/epoxy, experimentally. This paper shows the performance of the simulator.

Fundamental properties of 3D microfabrication using a femtosecond laser

Micro scaled grooves and cavities are fabricated with the method of direct writing and superposing grooving in ambient air using femtosecond laser pulses and copper, aiming at establishing an industrially useful femtosecond laser processing machine to be able to fabricate three dimensional micro-scale structures, especially micro scaled molds, and processing techniques. The following items are demanded to make femtosecond laser processing machine an industrially useful tool. (1) There is no thermally influenced region around the area irradiated by the laser beam. (2) Surfaces irradiated laser beam are smooth. (3) Substances ablated to form are not attached on the surface of the work. In this study, fundamental properties of grooving and cavity processing are investigated experimentally, considering above items, especially eyeing on the items (1) and (2). As a result obtained in this research, the method of direct writing and superposing grooving havs a potential to fabricate micro scaled structure.