Page 271 - Environmental Nanotechnology Applications and Impacts of Nanomaterials

256 Principles and Methods

a 10-nm particle is treated in the same manner as that of a 100-nm particle.
In fact, a range of behaviors may be observed for particles that are char-
acterized by sizes on two different ends of the nano-spectrum (1 to 100 nm).
For instance, the cases illustrated above were clusters of nanoparticles in
the larger nano-size fraction (d ~ 100 nm) as defined here. Indeed, as par-
ticle size approaches that of the lower size range (d < 50 nm) a deviation
from classical aggregation behavior emerges. This deviation is linked to
changes in the interfacial interactions that occur as particle size
approaches the nano-domain. To illustrate this point, let us consider the
findings of Kobayashi et al. [22], who observed a size effect on the aggre-
gation rate constant for particles of similar surface chemistries. Kobayashi
et al. [22] examined three different sizes of silica nanoparticles (80, 50, and
30 nm) and determined that only the aggregation of the 80 nm particles
followed predictions based on DLVO theory (Figure 7.14). Smaller 50 nm

Figure 7.14 Experimental results of the aggregation rate constants for silica particles as
a function of pH at different ionic strength: (a) d 80 nm, (b) d 50 nm, and (c) d 30
nm silica particles. The lines serve to guide the eye.