3 research outputs found
Pressure-Stimulated Supercrystal Formation in Nanoparticle Suspensions
Nanoparticles
can self-organize into “supercrystals”
with many potential applications. Different paths can lead to nanoparticle
self-organization into such periodic arrangements. An essential step
is the transition from an amorphous state to the crystalline one.
We investigate how pressure can induce a phase transition of a nanoparticle
model system in water from the disordered liquid state to highly ordered
supercrystals. We observe reversible pressure-induced supercrystal
formation in concentrated solutions of gold nanoparticles by means
of small-angle X-ray scattering. The supercrystal formation occurs
only at high salt concentrations in the aqueous solution. The pressure
dependence of the structural parameters of the resulting crystal lattices
is determined. The observed transition can be reasoned with the combined
effect of salt and pressure on the solubility of the organic PEG shell
that passivates the nanoparticles
Ligand Layer Engineering To Control Stability and Interfacial Properties of Nanoparticles
The use of mixed ligand layers including
poly(ethylene glycol)-based ligands for the functionalization of nanoparticles
is a very popular strategy in the context of nanomedicine. However,
it is challenging to control the composition of the ligand layer and
maintain high colloidal and chemical stability of the conjugates.
A high level of control and stability are crucial for reproducibility,
upscaling, and safe application. In this study, gold nanoparticles
with well-defined mixed ligand layers of α-methoxypoly(ethylene
glycol)-ω-(11-mercaptoundecanoate) (PEGMUA) and 11-mercaptoundecanoic
acid (MUA) were synthesized and characterized by ATR-FTIR spectroscopy
and gel electrophoresis. The colloidal and chemical stability of the
conjugates was tested by dynamic light scattering (DLS), small-angle
X-ray scattering (SAXS), and UV/vis spectroscopy based experiments,
and their interactions with cells were analyzed by elemental analysis.
We demonstrate that the alkylene spacer in PEGMUA is the key feature
for the controlled synthesis of mixed layer conjugates with very high
colloidal and chemical stability and that a controlled synthesis is
not possible using regular PEG ligands without the alkylene spacer.
With the results of our stability tests, the molecular structure of
the ligands can be clearly linked to the colloidal and chemical stabilization.
We expect that the underlying design principle can be generalized
to improve the level of control in nanoparticle surface chemistry
On the Spontaneous Formation of Clathrate Hydrates at Water–Guest Interfaces
The formation of hydrates, cage-like water-gas structures,
is of
tremendous importance both in industries and research. Although of
major significance, the formation process is not completely understood
so far. We present a comprehensive study of hydrate formation at liquid–liquid
interfaces between water and isobutane, propane, carbon dioxide, and
at the liquid–gas interface between water and xenon. We investigated
the structure of these interfaces under quiescent conditions in situ
by means of X-ray reflectivity measurements both inside and outside
the zone of hydrate stability. At the interfaces between water and
liquid alkanes, no evidence for a structural change was found. In
contrast, the accumulation of guest molecules inside nanothick interfacial
layers was observed at the water–xenon and liquid–liquid
water–CO<sub>2</sub> interfaces. We show that only those systems
initially exhibiting such guest-enriched interfacial layers developed
into macroscopic gas hydrates within our observation times (∼12
h). Therefore, these layers act as triggers for the spontaneous formation
of macroscopic hydrates