3 research outputs found
Assembly of Nanoparticles at Liquid Interfaces: Crowding and Ordering
Experiments
with the self-assembly of nanoparticles at liquid interfaces
suggest that cooperative and slow dynamical processes due to particle
crowding at the interface govern the adsorption and properties of
the final assembly. Here we report a numerical approach to studying
nonequilibrium adsorption, which elucidates these experimental observations.
The analysis of particle rearrangements shows that local ordering
processes are directly related to adsorption events at high interface
coverage. Interestingly, this feature and the mechanism coupling local
ordering to adsorption do not seem to change qualitatively upon increasing
particle size polydispersity, although the latter changes the interface
microstructure and its final properties. Our results indicate how
adsorption kinetics can be used for the fabrication of 2D nanocomposites
with controlled microstructure
Conformations and Effective Interactions of Polymer-Coated Nanoparticles at Liquid Interfaces
We investigate conformations and
effective interactions of polymer-coated
nanoparticles adsorbed at a model liquid–liquid interface via
molecular dynamics simulations. The polymer shells strongly deform
at the interface, with the shape governed by a balance between maximizing
the decrease in interfacial area between the two solvent components,
minimizing unfavorable contact between polymer and solvent, and maximizing
the conformational entropy of the polymers. Using potential of mean
force calculations, we compute the effective interaction between the
nanoparticles at the liquid–liquid interface. We find that
it differs quantitatively from the bulk and is significantly affected
by the length of the polymer chains and by the solvent quality. Under
good solvent conditions, the effective interactions are always repulsive
and soft for long chains. The repulsion range decreases as the solvent
quality decreases. In particular, under poor solvent conditions, short
chains may fail to induce steric repulsion, leading to a net attraction
between the nanoparticles, whereas with long-enough chains the effective
interaction potential may feature an additional repulsive shoulder
at intermediate distances
Dynamical Heterogeneity in the Supercooled Liquid State of the Phase Change Material GeTe
A contending
technology for nonvolatile memories of the next generation
is based on a remarkable property of chalcogenide alloys known as
phase change materials, namely their ability to undergo a fast and
reversible transition between the amorphous and crystalline phases
upon heating. The fast crystallization has been ascribed to the persistence
of a high atomic mobility in the supercooled liquid phase, down to
temperatures close to the glass transition. In this work we unravel
the atomistic, structural origin of this feature in the supercooled
liquid state of GeTe, a prototypical phase change compound, by means
of molecular dynamic simulations. To this end, we employed an interatomic
potential based on a neural network framework, which allows simulating
thousands of atoms for tens of ns by keeping an accuracy close to
that of the underlying first-principles framework. Our findings demonstrate
that the high atomic mobility is related to the presence of clusters
of slow and fast moving atoms. The latter contain a large fraction
of chains of homopolar Ge–Ge bonds, which at low temperatures
have a tendency to move by discontinuous cage-jump rearrangements.
This structural fingerprint of dynamical heterogeneity provides an
explanation of the breakdown of the Stokes–Einstein relation
in GeTe, which is the ultimate origin of the fast crystallization
of phase change materials exploited in the devices