Page 139 - Book Hosokawa Nanoparticle Technology Handbook

CHAPTER 3 CHARACTERISTICS AND BEHAVIOR OF NANOPARTICLES AND ITS
DISPERSION SYSTEMS

3.1 Introduction of nanoparticle concept and method for the aggregation and disper-
sion control will be reviewed.
dispersion and aggregation behavior

3.1.1. Surface interaction between nanoparticles
Recently, the technological innovation of low-cost and
large-scale synthesis process of nanoparticles with Since dispersed nanoparticles form aggregates in gas
less than 100 nm in diameter is developing, and vari- phase with the progress of the time, the dispersion and
ous kinds of nanoparticles are applied as the raw aggregation behavior of nanoparticles is generally con-
materials in the different fields, for example, cos- trolled in liquid phase. The main mechanisms of sur-
metic, medical supplies, catalysts, pigments, toner face interaction between particles in liquid phase are
and ink. Since the commercial products in such fields summarized in Table 3.1.1. The first and second items
are colloidal suspension with relatively low solid con- in this table, van der Waals force and electrostatic force
tent or powdery condition, it is rather easy to apply by the overlap of electric double layer had been sys-
nanoparticles for commercial product. On the con- tematized in famous DLVO theory [1]. If it is possible
trary, for the application of functional properties of to control the aggregation and dispersion behavior of
nanoparticles to new materials, it is difficult to pro- nanoparticles in liquid by the adjustment of electro-
duce the final commercial products. Nanoparticles static interaction, we can design the dispersion behav-
are expected to be raw materials for many kinds of ior by using DLVO theory. However, non-DLVO type
new functional materials, for example nanodevice interaction, steric, bridging and depletion force, is gen-
with high-density circuit and wiring in use of erally important to control dispersion behavior of
nanoparticles, two-dimensional high-density nanodot nanoparticles. The fundamentals of dispersion control
memory element, and hybrid composite materials in liquid are introduced based on DLVO theory.
with high-density packed nanoparticles. For the com-
mercial implementation of such materials, it needs to
develop many kinds of nanoparticle processing. For 3.1.2. Difficulty in nanoparticle dispersion control
nanometer-scaled devises, it is necessary to develop based on DLVO theory
nanoparticle dispersion in suspension without aggre-
gation, nanoparticles assemble on the circuit, drying DLVO theory is based on the van der Waals and elec-
and sintering technology to cause neither disconnec- trostatic interaction by the overlap of electric double
tion nor deformation. layer which is generated by the counter ions concen-
The aggregation/dispersion behavior control, which trated at the surface of particles by the surface charge.
is the first process for the preparation of new func- By using this theory, it is possible to discuss the disper-
tional materials using nanoparticles, is very difficult sion and aggregation behavior of particles in aqueous
for nanoparticles with less than 100 nm in diameter. suspension.
In this chapter, based on the introduction of the basic One example of potential curve of surface interaction
reason why the aggregation and dispersion behavior calculated by this theory is shown in Fig 3.1.1. Surface
control of nanoparticles is very difficult, the basic charge on particles and counter ion concentration in

Table 3.1.1
Examples of surface interaction between particles in liquid phase.
Surface interaction Generation mechanism
van der Waals interaction Short-ranged electromagnetic force between molecule and/or atoms, which
has neutral charge only.
Overlap of electric double layer Electrical interaction by the overlap of electric double layer around particle
in solution
Steric interaction of adsorbed polymer Short-ranged interaction by the overlap of adsorbed polymer layer on particles
Bridge force Formation of the bridge of polymer binder and/or surfactant between particles
Hydration force Overlap of hydrogen-bonded water molecule on hydrophilic surface on particle
Depletion Negative adsorption of solute and polymer by having less affinity for the
surface than the solvent

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