Some of the recent advancements in nanotechnology depend critically on how
nanoparticles move and diffuse on a surface or in a fluid under non-ideal to
extreme conditions. Georgia Institute of Technology (Georgia Tech) has a team
of researchers dedicated to advancing this frontier.
Rigoberto Hernandez, a professor in the School of Chemistry
and Biochemistry, investigates these relationships by studying 3D particle
dynamics simulations on high-performance computers. His new findings, which
focus on the movements of a spherical probe amongst static needles, are
published in The Journal of Physical Chemistry B.
Hernandez and his former PhD student, Ashley Tucker, assembled the rod-like
scatterers in one of two states during his simulations: Disordered (isotropic)
and ordered (nematic). When the nanorods were disordered, pointing in various
directions, Hernandez found that a particle typically diffused uniformly in all
directions. When every rod pointed in the same direction, the particle, on
average, diffused more in the same direction as the rods than against the grain
of the rods. In this nematic state, the probe’s movement mimicked the elongated
shape of the scatterers. The surprise was that the particles sometimes diffused
faster in the nematic environment than in the disordered environment. That is,
the channels left open between the ordered nanorods don’t just steer
nanoparticles along a direction, they also enable them to speed right through.
As the density of the scatterers is increased, the channels become more and
more crowded. The particle diffusing through these increasingly crowded
assemblies slows down dramatically in the simulation. Nevertheless, the
researchers found that the nematic scatterers continued to accommodate faster
diffusion than disordered scatterers.
“These simulations bring us a step closer to creating a nanorod device that
allows scientists to control the flow of nanoparticles,” said Hernandez. “Blue-sky applications of such devices include the creation of new light
patterns, information flow and other microscopic triggers.”
For example, if scientists need a probe to diffuse in a specific direction
at a particular speed, they could trigger the nanorods to move into a specified
direction. When they need to change the particle’s direction, scatterers could
then be triggered to rearrange into a different direction. Indeed, the trigger
could be the absence of sufficient nanoparticles in a given part of the device.
The ensuing reordering of the nanorods would then drive a repopulation of
nanoparticles that would then be available to perform a desired action, such as
to stimulate light flow.
“While this NSF-funded work to better understand the motion of particles
within complex arrays at the nanoscale is very fundamental,” Hernandez says, “it has significant long-term implications on device fabrication and
performance at such scales. It’s fun to think about and provides great training
for my students.”