13 research outputs found
Self-Assembly of AB Diblock Copolymer Confined in a Soft Nano-Droplet: A Combination Study by Monte Carlo Simulation and Experiment
The
self-assembly of AB-type diblock copolymers confined in a three-dimensional
(3D) soft nanodroplet is investigated by the combination of Monte
Carlo simulation and experiment. The influences of two critical factors,
i.e., confinement degree of the imposed confinement space and the
interfacial interaction between each individual block and boundary
interface, on the 3D soft confined self-assembly are examined systematically.
The simulation results reveal that block copolymer chains become more
and more folded as the confinement degree (it can be monitored by
the ratio of <i>D</i>/<i>L</i>, where <i>L</i> is the length of polymer chain and <i>D</i> is
the reduced diameter of the final polymeric particle) is enhanced,
causing a series of morphological transitions. Based on the simulation
prediction, we perform the corresponding experiments by the 3D confined
self-assembly of both symmetric and asymmetric block copolymers within
the emulsion droplets. The experimental results well reproduce the
confinement degree induced morphological transitions predicted by
the simulations, such as the transition from segmented pupa-like particle
to hamburger particle and the transition from raspberry-like particle
to triangle-like particle, and then to hamburger particle. The current
study implies that self-assembled nanostructures under 3D soft confinement
can be simply controlled by tuning the confinement degree and interfacial
property, i.e., the ratio of <i>D</i>/<i>L</i> and the interfacial interaction between each individual block and
boundary interface
Online Rheological Investigation on Ion-Induced Micelle Transition for Amphiphilic Polystyrene-<i>block</i>-Poly(acrylic acid) Diblock Copolymer in Dilute Solution
The ion-induced micellar transition
is online-investigated by the
time dependence of the viscosity of the solution under shear flow
for the first time. During the morphological transition, the change
in the micellar structure can be tracked by the change in viscosity.
Adding HCl or CaCl<sub>2</sub> into pre-prepared spherical micelle
solution from the self-assembly of polystyrene-<i>block</i>-poly(acrylic acid) (PS<sub>144</sub>-<i>b</i>-PAA<sub>22</sub>) in the <i>N</i>,<i>N</i>-dimethylformamide
(DMF)/water mixture, the micellar structures change into short cylinders,
long, entangled cylinders, and then lamellae or vesicles, corresponding
to the viscosity increasing first and then declining. When HCl or
CaCl<sub>2</sub> is added to the pre-prepared spherical micelle solution
formed by PS<sub>144</sub>-<i>b</i>-PAA<sub>50</sub> in
the dioxane/water mixture, the micellar structures are quickly transformed
into cylinders or lamellae before carrying out the rheological measurement
and then are turned to vesicles or spheres under the shearing, corresponding
to a gradual decline in viscosity. This study shows that the rheology
can be a very simple and effective online method on the investigation
of the micellization, which plays an important role in understanding
the micellization mechanism and micellar transition pathway of block
copolymers in dilute solution
Controllable Location of Inorganic Nanoparticles on Block Copolymer Self-Assembled Scaffolds by Tailoring the Entropy and Enthalpy Contributions
Precisely
controlling the spatial location and alignment of functional
nanoparticles (NPs) on polymeric scaffolds is of great importance
to not only create novel nanostructures but also enhance the properties
of the hybrid nanomaterials. Herein, we demonstrate a strategy of
tailoring the entropic and enthalpic contributions to precisely position
gold nanoparticles (AuNPs) on block copolymer (BCP) scaffolds through
the confined coassembly of BCPs and AuNPs within the emulsion droplet.
According to this strategy, entropic effect arisen by the loss in
conformational entropy and the enthalpic attraction between ligands
on AuNPs and surfactants at the oil/water interface induce the solid
AuNPs to move to the BCP surface, while the enthalpic interaction
between the ligands on AuNPs and the corresponding polymer chains
guides the AuNPs to position at the appropriate place. By this strategy,
both the location and alignment of AuNPs on BCP scaffolds can be controlled
at will, such as at the two terminals or along the lamellar boundary
of the pupa-like scaffolds, or at the bases of pinecone-like or bud-like
scaffolds, or at the head of one hemisphere, the entire hemisphere,
or along the boundary between the two distinct hemispheres of the
Janus-like scaffolds. We believe that this methodology can offer a
universal route to achieve the precise positioning of functional NPs
on the BCP scaffolds
Inorganic Nanoparticle Induced Morphological Transition for Confined Self-Assembly of Block Copolymers within Emulsion Droplets
Recently,
it has been reported that the incorporation of functional
inorganic nanoparticles (NPs) into the three-dimensional (3D) confined
self-assembly of block copolymers (BCPs) creates the unique nanostructured
hybrid composites, which can not only introduce new functions to BCPs
but also induce some interesting morphological transitions of BCPs.
In the current study, we systematically investigate the cooperative
self-assembly of a series of size-controlled and surface chemistry-tunable
gold nanoparticles (AuNPs) and polystyrene-<i>b</i>-poly(2-vinylpyridine)
(PS-<i>b</i>-P2VP) diblock copolymer within the emulsion
droplets. The influences of the size, content, and surface chemistry
of the AuNPs on the coassembled nanostructures as well as the spatial
distribution of AuNPs in the hybrid particles are examined. It is
found that the size and content of the AuNPs are related to the entropic
interaction, while the surface chemistry of AuNPs is related to the
enthalpic interaction, which can be utilized to tailor the self-assembled
morphologies of block copolymer confined in the emulsion droplets.
As the content of PS-coated AuNPs increases, the morphology of the
resulting AuNPs/PS-<i>b</i>-P2VP hybrid particles changes
from the pupa-like particles to the bud-like particles and then to
the onion-like particles. However, a unique morphological transition
from the pupa-like particles to the mushroom-like particles is observed
as the content of P4VP-coated AuNPs increases. More interestingly,
it is observed that the large AuNPs are expelled to the surface of
the BCP particles to reduce the loss in the conformational entropy
of the block segment, which can arrange into the strings of necklaces
on the surfaces of the hybrid particles
Gold-Catalyzed [4 + 1] Heterocyclization of Hydroxamic Acid and Nonactivated Alkyne: A Protocol to Construct 5‑Methyl-1,4,2-dioxazole
A novel gold-catalyzed [4 + 1] heterocyclization of nonactivated
alkyne and hydroxamic acid is developed for the regiospecific synthesis
of 5-methyl-1,4,2-dioxazole, which is an important structural motif
in various bioactive molecules. The current methodology is characterized
by high efficiency, simple operation, mild reaction conditions, and
good functional group compatibility. Moreover, gram-scale synthesis
and synthetic application toward bioactive molecular skeletons have
been realized
Entropy-Driven Hierarchical Nanostructures from Cooperative Self-Assembly of Gold Nanoparticles/Block Copolymers under Three-Dimensional Confinement
The
cooperative self-assembly of polystyrene-<i>b</i>-poly(4-vinylpyridine)
block copolymers (BCPs) and gold nanoparticles
(AuNPs) confined within the emulsion droplets is studied by combining
both the experiments and Monte Carlo simulations. The results indicate
that the entropic interaction between the AuNPs and BCP domain is
a critical parameter to dominate the spatial arrangement of AuNPs
and the nanostructure of the hybrid nanoparticles, which can be utilized
to design novel hierarchical hybrid nanoparticles. Based on this theoretical
observation, a large number of unique Janus hybrid nanoparticles,
including pupa-like nanoparticles with AuNPs concentrated at one pole
of the particles, spherical nanoparticles with AuNPs enriched in a
bulge on the sphere surface, and the gourd-like, clover-like, and
four-leaf-clover-like nanoparticles from the further hierarchical
assembly of small hybrid Janus nanoparticles, are fabricated via three-dimensional
(3D) confined self-assembly
Synthesis of Novel Two-Phase Co@SiO<sub>2</sub> Nanorattles with High Catalytic Activity
Noble
metal nanocatalysts with remarkable catalytic properties have attracted
much attention; however, the high cost of these materials limits their
industrial applications. Here, we design and prepare Co@SiO<sub>2</sub> nanorattles as a mixture of hcp-Co and fcc-Co phases as a substitute.
The nanorattles exhibit both superior catalytic activity and high
stability for the reduction of <i>p</i>-nitrophenol. The
reduction rate nearly follows pseudo-first-order kinetics, and the
reaction rate constant is as high as 0.815 min<sup>–1</sup> and is maintained at 0.565 min<sup>–1</sup> even after storing
for one month, which is higher than that reported for noble metal
nanocatalysts. Such an excellent property can be attributed to the
novel two-phase composition and rattle-type structure
Size- and Shape-Dependent Photoexcitation Electron Transfer in Metal Nanoclusters
There are some unresolved fundamental issues for metal
nanoclusters;
for instance, the close-packed structure transformation from face-centered
cubic (fcc) to hexagonal close-packed (hcp) has not yet been reported,
and photoexcitation electron transfer is not well understood. Herein,
we realized for the first time the fcc-to-hcp structure transformation
and revealed the size- and shape-dependent photoexcitation electron
transfer for metal nanoclusters. Specifically, a thermally induced
ligand exchange method was developed, and a rod-shaped hcp Au42(SCH2Ph)32 (HSCH2Ph: benzyl
mercaptan) with the largest aspect ratio was synthesized from fcc
Au28(SPh-tBu)20 (HSPh-tBu: p-tert-butylphenol) and structurally resolved, which shows a sharp absorption
at 815 nm and dual emission that is well interpreted by time-dependent
density functional theory (TD-DFT) calculations. The structure transformation
pathway was proposed, and a novel, rod-shaped hcp Au58(SR)40 with larger aspect ratio was predicted. Interestingly, it
is found that the kernel-based middle-to-both ends sp ← sp
photoexcitation electron transfer can be extended to other rod-like
(one-dimensional) gold nanoclusters, and the major photoexcitation
turns to the kernel-based sp ← sp transition from the staple-to-kernel
sp ← d transition when the spherical gold nanocluster size
is increased to Au42 and the Au(6sp) composition increases
with increasing size for structure-similar nanoclusters. These findings
deepen our understanding of metal nanocluster photoexcitation electron
transfer and provide guidance for future nanocluster property tuning
aimed at practical applications
Size- and Shape-Dependent Photoexcitation Electron Transfer in Metal Nanoclusters
There are some unresolved fundamental issues for metal
nanoclusters;
for instance, the close-packed structure transformation from face-centered
cubic (fcc) to hexagonal close-packed (hcp) has not yet been reported,
and photoexcitation electron transfer is not well understood. Herein,
we realized for the first time the fcc-to-hcp structure transformation
and revealed the size- and shape-dependent photoexcitation electron
transfer for metal nanoclusters. Specifically, a thermally induced
ligand exchange method was developed, and a rod-shaped hcp Au42(SCH2Ph)32 (HSCH2Ph: benzyl
mercaptan) with the largest aspect ratio was synthesized from fcc
Au28(SPh-tBu)20 (HSPh-tBu: p-tert-butylphenol) and structurally resolved, which shows a sharp absorption
at 815 nm and dual emission that is well interpreted by time-dependent
density functional theory (TD-DFT) calculations. The structure transformation
pathway was proposed, and a novel, rod-shaped hcp Au58(SR)40 with larger aspect ratio was predicted. Interestingly, it
is found that the kernel-based middle-to-both ends sp ← sp
photoexcitation electron transfer can be extended to other rod-like
(one-dimensional) gold nanoclusters, and the major photoexcitation
turns to the kernel-based sp ← sp transition from the staple-to-kernel
sp ← d transition when the spherical gold nanocluster size
is increased to Au42 and the Au(6sp) composition increases
with increasing size for structure-similar nanoclusters. These findings
deepen our understanding of metal nanocluster photoexcitation electron
transfer and provide guidance for future nanocluster property tuning
aimed at practical applications
Co<sub>3</sub>O<sub>4</sub> Nanocages for High-Performance Anode Material in Lithium-Ion Batteries
Co<sub>3</sub>O<sub>4</sub> nanoparticles have been prepared
by
a facile strategy, which involves the thermal decomposition of nanoparticles
of cobalt-based Prussian blue analogues at different temperatures.
The nanoparticles prepared at 450, 550, 650, 750, and 850 °C
exhibited a high discharge capacity of 800, 970, 828, 854, and 651
mAhg<sup>–1</sup>, respectively, after 30 cycles at a current
density of 50 mAg<sup>–1</sup>. The nanocages produced at 550
°C show the highest lithium storage capacity. It is found that
the nanocages display nanosize grains, hollow structure, a porous
shell, and large specific surface area. At the temperature higher
than 650 °C, the samples with larger grains, better crystallinity,
and lower specific surface area can be obtained. It is found that
the size, crystallinity, and morphology of nanoparticles have different
effects on electrochemical performance. Better crystallinity is able
to enhance the initial discharge capacity, while porous structure
can reduce the irreversible loss. Therefore, the optimal size, crystallinity,
and cage morphology are suggested to be responsible for the improved
lithium storage capacity of the sample prepared at 550 °C. The
as-prepared Co<sub>3</sub>O<sub>4</sub> nanoparticles also have a
potential application as anode material for Li-ion batteries due to
their simple synthesis method and large capacity