4 research outputs found
Shape-Tailored Colloidal Molecules Obtained by Self-Assembly of Model Gold Nanoparticles with Flexible Polyelectrolyte
We
study for the first time the structure of stable finite size
clusters (i.e., colloidal molecules) obtained by self-assembly of
cationic gold nanoparticles (i.e., atoms) mediated by a flexible polyanion.
We reveal with nondenaturizing techniques a striking structural transition
from 1D small chains of 12 gold nanoparticles (AuNPs) with a self-avoiding
conformation to 3D fractal clusters of 130 AuNPs with short-range
ordering around the charge inversion threshold. Interestingly, these
well-defined structures are obtained by simple mixing in water without
anisotropic functionalization or external forces. As a preliminary
step, we introduce a new synthesis pathway leading to well-defined
cationic AuNPs of controllable size that can be dispersed in H<sub>2</sub>O or D<sub>2</sub>O without aggregation and ligands’
self-assemblies. On this occasion, we point for the first time that
usual procedures do not enable to eliminate cationic ligands’
self-assemblies that could play an undesired role in AuNPs’
self-assembly through electrostatic interactions
Metastability of Large Aggregates and Viscosity, and Stability of The Pearl Necklace Conformation After Organic Solvent Treatment Of Aqueous Hydrophobic Polyelectrolyte Solutions
Aggregatesa
phenomenon still not understoodas well
as the pearl-necklace-like chain conformation in aqueous solutions
of hydrophobic polyelectrolytes are addressed here, using treatment
by an organic solvent. The second appear to be at equilibrium in water.
The first appear to be metastable, and surprisingly associated with
higher zero shear viscosity. The hydrophobic polyelectrolyte is poly(styrene-<i>co</i>-sodium styrenesulfonate) (PSS), and the solution treatment
is to first add to water an organic solvent, THF, which is then evaporated
and replaced by the same amount of water. To investigate polyelectrolyte
solutions as a function of THF treatment, we use small angle neutron
scattering in the semidilute regime, viscosimetry in the dilute and
semidilute regimes (unentangled), and osmometry in the similar semidilute
regime (the contribution of the counterions being dominant). First,
the structure, namely, the scattering from all chains, is characterized
by a maximum (“polyelectrolyte peak”). Its position,
amplitude, and scattered intensity at zero angle depend, at a given
sulfonation rate of PSS, on the solvent quality through the added
amount of organic solvent (THF). This dependence is very pronounced
when the sulfonation rate is low (more hydrophobic polyelectrolyte)
and is canceled when the sulfonation rate is high (more hydrophilic
polyelectrolyte). Second, the viscosity of the polyelectrolyte solutions
decreases with THF treatment for the hydrophobic polyelectrolytes.
Third, osmometry shows no noticeable increase of the effective charge
with THF treatment. It is proposed that the large scale aggregates,
especially in the case of very hydrophobic polyelectrolytes, disappear
irreversibly with THF treatment, while the pearl-necklace conformation
of the chain remains as in its initial state. Parallel test measurements
for a fully hydrophilic polyelectrolyte, poly(sodium-2-acrylamido-2-methylpropanesulfonate)-<i>co</i>-(acrylamide) (P(AMAMPS)), at different sulfonation rates,
show no evolution of the structure with THF treatment in the aqueous
solution. The same behavior is highlighted by viscosimetry