53 research outputs found
Fabrication of Large-Area Two-Dimensional Microgel Colloidal Crystals via Interfacial ThiolâEne Click Reaction
A method
for the fabrication of high quality, large area 2D colloidal crystals
(CCs) using polyÂ(<i>N</i>-isopropylÂacrylamide) (PNIPAM)
microgel sphere, an extremely soft colloid, as building block was
proposed. First the microgel spheres were assembled into 3D colloidal
crystals. The first 111 plane of the 3D crystal close to the substrate
was then fixed <i>in situ</i> onto the substrate. Highly
efficient photoinitiated thiolâene coupling was chosen for
the fixing purpose. Thanks to the high quality of 3D microgel CCs,
the resulting 2D CCs exhibit a high degree of ordering. Large area
2D CCs were fabricated because large area 3D microgel CCs can be facilely
fabricated. Besides planar substrates, the method allows the fabrication
of 2D CCs on curved surface, too. In addition, the interpartical distance
in the 2D CCs can be tuned by the concentration of the microgel dispersion
OrderâDisorder Transition in Doped Microgel Colloidal Crystals and Its Application for Optical Sensing
Hydrogel
photonic crystal-based optical sensors usually can only be used as
free-standing films. Here, a doped microgel colloidal crystal film
was developed as glucose sensor, which exploits structural orderâdisorder
transition, instead of change in lattice constant, to report an analyte.
Changing glucose concentration induces a change in structural order
degree in the crystal and hence a change in the intensity of the stop
band, and thus reports glucose concentration in the media. The response
is fast and reversible. As the overall swelling degree of the gel
does not change, it can be used as substrate-attached film
Fractal Structures of the Hydrogels Formed in Situ from Poly(<i>N</i>-isopropylacrylamide) Microgel Dispersions
Dispersions of polyÂ(<i>N</i>-isopropylacrylamide)
(PNIPAM)
microgel thermally gel in the presence of inorganic salts. The in
situ-formed hydrogels, with a network of soft particles, represent
a new type of colloidal gels. Here, their fractal structures were
determined by rheological measurements, using the models of both Shih
et al. and Wu and Morbidelli. According to the definition of Shih
et al., the colloidal PNIPAM gels fall into the strong-link regime.
Yet the calculated fractal dimension of the floc backbone, <i>x</i>, yielded unrealistic negative values, suggesting this
model is inapplicable for the present system. The WuâMorbidelli
model gives physically sounder results. According to this model, the
strengths of the inter- and intrafloc links are comparable, and the
in situ-formed gels are in the transition regime. The fractal dimension, <i>d</i><sub>f</sub>, of the hydrogel decreases from âŒ2.5
to âŒ1.8 when the heating temperature increases from 34 to 40
°C. The <i>d</i><sub>f</sub> values suggest different
aggregation mechanisms at different temperatures, that is, a reaction-limited
one accompanied by rearrangement at low temperature, a typical reaction-limited
one at the intermediate temperature, and a diffusion-limited one at
high temperature. With increasing salt concentration, the <i>d</i><sub>f</sub> of the hydrogel decreases from âŒ2.1
to âŒ1.7, suggesting the aggregation mechanism changes from
reaction-limited to diffusion-limited. The effects of both temperature
and salt concentration can be explained by the changes in the interactions
among the microgel particles. The thermogellable PNIPAM microgel dispersions
may serve as a model system for the study of heat-induced gelation
of globular proteins
Glucose-Induced Transition among Three States of a Doped Microgel Colloidal Crystal
For the first time
here, we report a colloid crystal capable of
undergoing transition among three states in response to external stimuli.
The colloidal crystal was assembled from polyÂ(<i>N</i>-isopropylacrylamide)
(PNIPAM) microgel and doped with polyÂ(<i>N</i>-isopropylacrylamide-<i>co</i>-2-acrylamido-phenylboronic acid) (PÂ(NIPAM-2-AAPBA)) microgel.
The ordered structure was locked by in situ photopolymerization. Taking
advantage of the different responses of the two microgels to external
stimuli, defect state can be induced and erased reversibly. Particularly,
because the dopant, that is, PÂ(NIPAM-2-AAPBA) microgel sphere, shrinks
with increasing glucose concentration, its size changes from larger
than the host, that is, PNIPAM microgel sphere, to equal to the host,
and finally smaller than the host. Therefore, upon addition of glucose,
the crystal undergoes transition from a state with acceptor-type defect,
to no defect state, and then to a state with donor-type defect. The
transition among the three states is fully reversible. In addition,
the response of the doped crystal to glucose is relatively fast
Dynamic Layer-by-Layer Films: A Platform for Zero-Order Release
Zero-order release is the ultimate
goal of controlled drug release
systems, however, it still remains a big challenge despite of numerous
previous efforts. Here we show that the release of PÂ(AAm-3-AAPBA)
from PÂ(AAm-3-AAPBA)/PVA film, a dynamic layer-by-layer (LBL) film,
follows a perfect zero-order kinetics, provided that both polymers
in the film have a narrow molecular weight distribution. Instead of
releasing via diffusion or degradation, PÂ(AAm-3-AAPBA) is released
from the film via the dissociation of the interpolymer complex. The
release rate is determined by molecular weight of the polymers. One
could also tune the release rate via various external environmental
stimuli, including pH, temperature, and glucose. The results suggest
dynamic LBL film could serve as a new drug release platform that allows
for not only zero-order release, but also intelligent release
Tetrahedral, Octahedral, and Triangular Dipyramidal Microgel Clusters with Thermosensitivity Fabricated from Binary Colloidal Crystals Template and ThiolâEne Reaction
A template-based
strategy to fabricate soft colloidal clusters
with distinct symmetries of tetrahedra, octahedra, and triangular
dipyramid is described. We use binary microgel colloidal crystals
as a template, in which the large microgels with surface thiol groups
are arranged into a close-packed lattice and a few small microgels
with surface vinyl groups occupy the tetrahedral or octahedral interstitial
sites, and then immobilize the structure via in situ thiolâene
reaction under UV irradiation. Both 2D cross sections and reconstructed
3D morphology of these clusters are clearly characterized by confocal
laser scanning microscopy. The formation mechanism of microgel clusters
is discussed, which is closely related to the microgel soft properties,
size ratio, and colloidal crystal packing structure. The resulting
clusters inherit the thermosensitivity and defects tolerance of polyÂ(<i>N</i>-isopropylacrylamide) (PNIPAM) microgel, which would facilitate
their self-assembly into more complex structures
Table_1_The use of generalized synthetic control method to evaluate air pollution control measures of G20 Hangzhou Summit.DOCX
The traditional campaign-style enforcement in environmental governance has been debated whether its rebound effect is likely to eat away the short-term environmental benefits and subsequently bring about severer pollution. There are methodological challenges in assessing the effect of temporary environmental intervention. By applying the generalized synthetic control method (GSCM), we quantified and characterized the effectiveness of environmental regulations implemented for the G20 Hangzhou Summit held on 4â5 September, 2016. The summit was successful in reducing Air Quality Composite Index by 17.40% (95% CI: 9.53%, 24.60%), 13.30% (95% CI: 4.23%, 21.50%), and 10.09% (95% CI: 2.01%, 17.51%) in the core, strictly-regulated and regulated areas respectively, comparing with the index expected under a âNo-G20â scenario during the preparatory period and the summit period (JulyâSeptember 2016), and the reduction of the levels in specific pollutants (PM10, PM2.5, NO2, and CO) was also observed. Besides, the environmental benefits lasted for at least 3 months after the summit. This study demonstrates that the pollution control measures during the G20 Hangzhou Summit improved air quality immediately and continuously, and the GSCM provides a useful tool for evaluating the intervention effects of environmental regulations.</p
Tetrahedral, Octahedral, and Triangular Dipyramidal Microgel Clusters with Thermosensitivity Fabricated from Binary Colloidal Crystals Template and ThiolâEne Reaction
A template-based
strategy to fabricate soft colloidal clusters
with distinct symmetries of tetrahedra, octahedra, and triangular
dipyramid is described. We use binary microgel colloidal crystals
as a template, in which the large microgels with surface thiol groups
are arranged into a close-packed lattice and a few small microgels
with surface vinyl groups occupy the tetrahedral or octahedral interstitial
sites, and then immobilize the structure via in situ thiolâene
reaction under UV irradiation. Both 2D cross sections and reconstructed
3D morphology of these clusters are clearly characterized by confocal
laser scanning microscopy. The formation mechanism of microgel clusters
is discussed, which is closely related to the microgel soft properties,
size ratio, and colloidal crystal packing structure. The resulting
clusters inherit the thermosensitivity and defects tolerance of polyÂ(<i>N</i>-isopropylacrylamide) (PNIPAM) microgel, which would facilitate
their self-assembly into more complex structures
Antioxidant capacity of phenolics in <i>Camellia nitidissima</i> Chi flowers and their identification by HPLC Triple TOF MS/MS - Fig 7
<p>Principal component analysis (PCA) loading plot of total phenolic content (TPC) and antioxidant activity of the ethanolic extract (A) dichloromethane fraction (B), ethyl acetate fraction (C), <i>n</i>-butanol fraction (D), and water fraction (E) of <i>C</i>. <i>nitidissima</i> Chi flowers.</p
Total phenolic content in the five fractions of <i>C</i>. <i>nitidissima</i> Chi flowers.
<p>Each value is expressed as mean ± SD (n = 3). Different letters showed significant differences from each other.</p
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