(393aa) Development of an Integrated Computational and Experimental Framework for Understanding and Controlling Nanoparticle Interactions

Nanomaterials hold vast potential for novel, more efficient, and
"greener" processes and products due to unique properties that are
fundamentally different from their bulk counterparts. These properties, in
combination with their extremely small size, make nanoparticles of great
interest for use as building blocks in the assembly of complex functional
materials to be used in a multitude of applications from electronic devices to
new construction materials with truly unique properties. Nanoparticles are also
already used in a variety of industrial products and processes, from which they
will be released into the environment where their "nanoproperties" may have
negative impacts on human health and the environment. Thus, a better
understanding of the fundamental interaction forces between nanoparticles would
not only provide significant aid in the development and manufacture of complex
functional nanomaterials, but may more importantly provide a means for
predicting or even controlling the toxicity of nanomaterials. Controlling the
interactions between nanoparticles could have vast implications concerning
human welfare, as well as environmental health and safety, in view of the
ever-increasing use of nanomaterials.

While the interaction forces governing both the macroscopic and
molecular size regimes are well understood, our understanding of the
interactions that govern the nanoscale regime (i.e., 1  - 100 nm) is only poorly developed to
date.  Continuum theories, which
allow description of the macroscopic regime, break down as particle sizes
approach the nanoscale regime. At the same time, atomistic simulations, which
can describe interactions on an atomic scale, become impractical due to the
large number of atoms in systems composed of collections of nanoparticles. 

Using silica as a base model, we are developing a bottom-up framework
based on material specific properties, for accurately modeling both static and
dynamic nanoparticle systems. First an interparticle potential is constructed
by contributions from van der Waals and electrostatic forces, both of which are
implemented via a form of coarse-grained molecular dynamics.  Van der Waals forces are accounted for
by packing small silica clusters, represented as single points, into the
particle geometry. Electrostatics are modeled by calculating the sum of
electrostatic interactions between silica nanoparticles for which atomic
charges were determined with a large-scale DFT implementation and the resulting
electron density gradient fitted to a function dependent on particle size.
Validation of the model is completed with the colloidal probe technique in
atomic force microscopy (AFM). An accurate interparticle potential can then be
implemented in dissipative particle dynamics (DPD) to simulate large nanoparticle
systems.

The proposed model, and the insight it would provide, may allow for
predicting or even controlling the toxicity of current nanomaterials and guide
the development of novel functional materials constructed via self-assembly.