Page 194 - Book Hosokawa Nanoparticle Technology Handbook

FUNDAMENTALS CH. 3 CHARACTERISTICS AND BEHAVIOR OF NANOPARTICLES AND ITS DISPERSION SYSTEMS
be the functional materials that cannot be produced methods such as the discrete element method (DEM)
from homogeneous systems, and the engineering and the Stokesian Dynamics (SD) [1] also have shown
tools for predicting the behavior in heterogeneous their application for micron-sized or larger particles.
systems would be highly desired because they would The only lack is the simulation method from several
speed up precise development, without which one nanometers to submicron sizes, or the mesoscale sim-
must undergo carpet bombing or rely only upon ulation techniques, for engineering applications.
empirical knowledge. This gap makes it impossible to connect molecular
This section describes a possible scheme for pre- properties to macroscopic phenomena. The quantum
dicting the behavior of mesoscale particulate systems mechanics, for example, can provide intermolecular
by appropriate combination of simulations for mole- interaction energies that can be applied to molecular
cules and colloidal dispersions, based on the micro- simulations, which can bridge the atomic scale to the
scopic molecular properties such as intermolecular molecular scale. However the SD, for example, is not
potential functions. The scheme must take multi- supported by a simulation technique just under itself.
scale structure to handle far different sizes of simula- Thus one would have to conduct a molecular simula-
tion elements such as simple molecules, complex tion with the size of micronscale, which is excessively
molecules like surfactants and polymers, mesoscale huge for molecules, if one would try to obtain surface
particles, and macroscopic flow-fields. What is forces based upon molecular properties. For the
important in this multi-scale structure is to connect moment, the interparticle forces can only be obtained
each unit with appropriate information that contains through the direct measurement by Atomic Force
molecular-level properties, with which microscopic Microscopy (AFM), or through the theoretical predic-
properties can be correctly reflected in a tion standing on continuum assumption, e.g., by the
meso/macroscopic behavior: The interaction forces DLVO theory for electrostatic systems. In all cases
between the simulation elements are to bridge them the pathway from the molecular-level properties are
as described later. Standing on this “bridging closed.
scheme”, notable simulation techniques are reviewed
and a possible structure composed of them will be (ii) A possible pathway from microscale properties to
discussed.
macroscopic dynamics
a. Brownian dynamics
3.8.1 Space–time mapping of simulation methods Figure 3.8.1 schematically shows a structure in the
space–time mapping that can bridge the gap in
(i) A gap lying in the mesoscale the mesoscale. (Note that the figure shows a typical
There have been many examples of application of time and space scale in which each technique is
molecular simulation methods for engineering pur- applied, and does not show the limit for the simulation
poses in the microscale, while in the macroscopic technique.)

3
10 s
AFM
Surface
force DEM
0
10 s Stokesian
Dynamics
Brownian
Time scale Surface
-3
Dynamics
10 s
force
Langevin
-6
10 s
Dynamics Surface
force
Molecular
-9
10 s Dynamics PMF
Quantum
Mechanics Intermolecular force
-6
-3
-9
10 m 10 m 0 m
Space scale
Figure 3.8.1
Space–time mapping of simulation methods for possible micro-macro connection.
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