Page 304 - Environmental Nanotechnology Applications and Impacts of Nanomaterials

Nanoparticle Transport, Aggregation, and Deposition 289

changes with particle size. It is therefore imperative that size effects on
interfacial interaction energies be considered, particularly given that
some interactions may become significant for nanoparticles that may
otherwise not be so for colloidal-sized materials of the same composition
(e.g., hydration interactions and silica particles).
The surface reactivity of suspended particles is a key parameter that
controls their interaction with other materials that may be present in sus-
pension, and thus their behavior in the given dispersion; even more so for
nanoparticles, for which their large surface area to volume ratio induces
a high sorption capacity for foreign species. The nature of these interac-
tions is always specific to the chemical characteristics of the nanoparti-
cles, and their affinity for the foreign species present in the system. In
many cases, adsorption occurs through charge-mediated interactions, or
via the formation of specific chemical bonds. In most cases, bond forma-
tion between nanoparticles and other materials results in a modification
of the surface reactivity of both, tending to lower the system free energy.
This favors intraparticle attractions and aggregation. One obvious exam-
ple of this phenomenon is the absorption and embedding of nanoparticles
into organo-mineral flocs, which cloaks the properties of the nanoparti-
cles producing transport and fate behavior that is determined by the floc.
Similarly, adsorption or reaction with other materials will affect nanopar-
ticles’ fate and transport.

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