13 research outputs found
The Crucial Role of Solvation Forces in the Steric Stabilization of Nanoplatelets
The steric stability
of inorganic colloidal particles in an apolar
solvent is usually described in terms of the balance between three
contributions: the van der Waals attraction, the free energy of mixing,
and the ligand compression. However, in the case of nanoparticles,
the discrete nature of the ligand shell and the solvent has to be
taken into account. Cadmium selenide nanoplatelets are a special case.
They combine a weak van der Waals attraction and a large facet to
particle size ratio. We use coarse grained molecular dynamics simulations
of nanoplatelets in octane to demonstrate that solvation forces are
strong enough to induce the formation of nanoplatelet stacks and by
that have a crucial impact on the steric stability. In particular,
we demonstrate that for sufficiently large nanoplatelets, solvation
forces are proportional to the interacting facet area, and their strength
is intrinsically tied to the softness of the ligand shell
The Crucial Role of Solvation Forces in the Steric Stabilization of Nanoplatelets
The steric stability
of inorganic colloidal particles in an apolar
solvent is usually described in terms of the balance between three
contributions: the van der Waals attraction, the free energy of mixing,
and the ligand compression. However, in the case of nanoparticles,
the discrete nature of the ligand shell and the solvent has to be
taken into account. Cadmium selenide nanoplatelets are a special case.
They combine a weak van der Waals attraction and a large facet to
particle size ratio. We use coarse grained molecular dynamics simulations
of nanoplatelets in octane to demonstrate that solvation forces are
strong enough to induce the formation of nanoplatelet stacks and by
that have a crucial impact on the steric stability. In particular,
we demonstrate that for sufficiently large nanoplatelets, solvation
forces are proportional to the interacting facet area, and their strength
is intrinsically tied to the softness of the ligand shell
The Crucial Role of Solvation Forces in the Steric Stabilization of Nanoplatelets
The steric stability
of inorganic colloidal particles in an apolar
solvent is usually described in terms of the balance between three
contributions: the van der Waals attraction, the free energy of mixing,
and the ligand compression. However, in the case of nanoparticles,
the discrete nature of the ligand shell and the solvent has to be
taken into account. Cadmium selenide nanoplatelets are a special case.
They combine a weak van der Waals attraction and a large facet to
particle size ratio. We use coarse grained molecular dynamics simulations
of nanoplatelets in octane to demonstrate that solvation forces are
strong enough to induce the formation of nanoplatelet stacks and by
that have a crucial impact on the steric stability. In particular,
we demonstrate that for sufficiently large nanoplatelets, solvation
forces are proportional to the interacting facet area, and their strength
is intrinsically tied to the softness of the ligand shell
The Crucial Role of Solvation Forces in the Steric Stabilization of Nanoplatelets
The steric stability
of inorganic colloidal particles in an apolar
solvent is usually described in terms of the balance between three
contributions: the van der Waals attraction, the free energy of mixing,
and the ligand compression. However, in the case of nanoparticles,
the discrete nature of the ligand shell and the solvent has to be
taken into account. Cadmium selenide nanoplatelets are a special case.
They combine a weak van der Waals attraction and a large facet to
particle size ratio. We use coarse grained molecular dynamics simulations
of nanoplatelets in octane to demonstrate that solvation forces are
strong enough to induce the formation of nanoplatelet stacks and by
that have a crucial impact on the steric stability. In particular,
we demonstrate that for sufficiently large nanoplatelets, solvation
forces are proportional to the interacting facet area, and their strength
is intrinsically tied to the softness of the ligand shell
The Crucial Role of Solvation Forces in the Steric Stabilization of Nanoplatelets
The steric stability
of inorganic colloidal particles in an apolar
solvent is usually described in terms of the balance between three
contributions: the van der Waals attraction, the free energy of mixing,
and the ligand compression. However, in the case of nanoparticles,
the discrete nature of the ligand shell and the solvent has to be
taken into account. Cadmium selenide nanoplatelets are a special case.
They combine a weak van der Waals attraction and a large facet to
particle size ratio. We use coarse grained molecular dynamics simulations
of nanoplatelets in octane to demonstrate that solvation forces are
strong enough to induce the formation of nanoplatelet stacks and by
that have a crucial impact on the steric stability. In particular,
we demonstrate that for sufficiently large nanoplatelets, solvation
forces are proportional to the interacting facet area, and their strength
is intrinsically tied to the softness of the ligand shell
Subnanometer Local Temperature Probing and Remotely Controlled Drug Release Based on Azo-Functionalized Iron Oxide Nanoparticles
Local heating can be produced by
iron oxide nanoparticles (IONPs)
when exposed to an alternating magnetic field (AMF). To measure the
temperature profile at the nanoparticle surface with a subnanometer
resolution, here we present a molecular temperature probe based on
the thermal decomposition of a thermo-sensitive molecule, namely,
azobisÂ[<i>N</i>-(2-carboxyethyl)-2-methylpropionamidine].
Fluoresceineamine (FA) was bound to the azo molecule at the IONP surface
functionalized with polyÂ(ethylene glycol) (PEG) spacers of different
molecular weights. Significant local heating, with a temperature increase
up to 45 °C, was found at distances below 0.5 nm from the surface
of the nanoparticle, which decays exponentially with increasing distance.
Furthermore, the temperature increase was found to scale linearly
with the applied field at all distances. We implemented these findings
in an AMF-triggered drug release system in which doxorubicin was covalently
linked at different distances from the IONP surface bearing the same
thermo-labile azo molecule. We demonstrated the AMF triggered distance-dependent
release of the drug in a cytotoxicity assay on KB cancer cells
Controlled Release of Doxorubicin Loaded within Magnetic Thermo-responsive Nanocarriers under Magnetic and Thermal Actuation in a Microfluidic Channel
We report a procedure to grow thermo-responsive polymer shells at the surface of magnetic nanocarriers made of multiple iron oxide superparamagnetic nanoparticles embedded in poly(maleic anhydride-<i>alt</i>-1-ocatadecene) polymer nanobeads. Depending on the comonomers and on their relative composition, tunable phase transition temperatures in the range between 26 and 47 °C under physiological conditions could be achieved. Using a suitable microfluidic platform combining magnetic nanostructures and channels mimicking capillaries of the circulatory system, we demonstrate that thermo-responsive nanobeads are suitable for localized drug delivery with combined thermal and magnetic activation. Below the critical temperature nanobeads are stable in suspension, retain their cargo, and cannot be easily trapped by magnetic fields. Increasing the temperature above the critical temperature causes the aggregation of nanobeads, forming clusters with a magnetic moment high enough to permit their capture by suitable magnetic gradients in close proximity to the targeted zone. At the same time the polymer swelling activates drug release, with characteristic times on the order of one hour for flow rates of the same order as those of blood in capillaries
Nanoscale Transformations in Covellite (CuS) Nanocrystals in the Presence of Divalent Metal Cations in a Mild Reducing Environment
We
studied the structural and compositional transformations of
colloidal covellite (CuS) nanocrystals (and of djurleite (Cu<sub>1.94</sub>S) nanocrystals as a control) when exposed to divalent cations, as
Cd<sup>2+</sup> and Hg<sup>2+</sup>, at room temperature in organic
solvents. All the experiments were run in the absence of phosphines,
which are a necessary ingredient for cation exchange reactions involving
copper chalcogenides, as they strongly bind to the expelled Cu<sup>+</sup> ions. Under these experimental conditions, no remarkable
reactivity was indeed seen for both CuS and Cu<sub>1.94</sub>S nanocrystals.
On the other hand, in the covellite structure 2/3 of sulfur atoms
form covalent S–S bonds. This peculiarity suggests that the
combined presence of electron donors and of foreign metal cations
can trigger the entry of both electrons and cations in the covellite
lattice, causing reorganization of the anion framework due to the
rupture of the S–S bonds. In Cu<sub>1.94</sub>S, which lacks
S–S bonds, this mechanism should not be accessible. This hypothesis
was proven by the experimental evidence that adding ascorbic acid
increased the fraction of metal ions incorporated in the covellite
nanocrystals, while it had no noticeable effect on the Cu<sub>1.94</sub>S ones. Once inside the covellite particles, Cd<sup>2+</sup> and
Hg<sup>2+</sup> cations engaged in exchange reactions, pushing the
expelled Cu<sup>+</sup> ions toward the not-yet exchanged regions
in the same particles, or out to the solution, from where they could
be recaptured by other covellite nanoparticles/domains. Because no
good solvating agent for Cu ions was present in solution, they essentially
remained in the nanocrystals
Tuning and Locking the Localized Surface Plasmon Resonances of CuS (Covellite) Nanocrystals by an Amorphous CuPd<sub><i>x</i></sub>S Shell
We
demonstrate the stabilization of the localized surface plasmon
resonance (LSPR) in a semiconductor-based core–shell heterostructure
made of a plasmonic CuS core embedded in an amorphous-like alloyed
CuPd<sub><i>x</i></sub>S shell. This heterostructure is
prepared by reacting the as-synthesized CuS nanocrystals (NCs) with
Pd<sup>2+</sup> cations at room temperature in the presence of an
electron donor (ascorbic acid). The reaction starts from the surface
of the CuS NCs and proceeds toward the center, causing reorganization
of the initial lattice and amorphization of the covellite structure.
According to density functional calculations, Pd atoms are preferentially
accommodated between the bilayer formed by the S–S covalent
bonds, which are therefore broken, and this can be understood as the
first step leading to amorphization of the particles upon insertion
of the Pd<sup>2+</sup> ions. The position and intensity in near-infrared
LSPRs can be tuned by altering the thickness of the shell and are
in agreement with the theoretical optical simulation based on the
Mie–Gans theory and Drude model. Compared to the starting CuS
NCs, the amorphous CuPd<sub><i>x</i></sub>S shell in the
core–shell nanoparticles makes their plasmonic response less
sensitive to a harsh oxidation environment (generated, for example,
by the presence of I<sub>2</sub>)
Photocatalytic Water-Splitting Enhancement by Sub-Bandgap Photon Harvesting
Upconversion
is a photon-management process especially suited to water-splitting
cells that exploit wide-bandgap photocatalysts. Currently, such catalysts
cannot utilize 95% of the available solar photons. We demonstrate
here that the energy-conversion yield for a standard photocatalytic
water-splitting device can be enhanced under solar irradiance by using
a low-power upconversion system that recovers part of the unutilized
incident sub-bandgap photons. The upconverter is based on a sensitized
triplet–triplet annihilation mechanism (sTTA-UC) obtained in
a dye-doped elastomer and boosted by a fluorescent nanocrystal/polymer
composite that allows for broadband light harvesting. The complementary
and tailored optical properties of these materials enable efficient
upconversion at subsolar irradiance, allowing the realization of the
first prototype water-splitting cell assisted by solid-state upconversion.
In our proof-of concept device the increase of the performance is
3.5%, which grows to 6.3% if concentrated sunlight (10 sun) is used.
Our experiments show how the sTTA-UC materials can be successfully
implemented in technologically relevant devices while matching the
strict requirements of clean-energy production