Fabrication of Large-Area Two-Dimensional Microgel Colloidal Crystals via Interfacial Thiol–Ene Click Reaction

A method for the fabrication of high quality, large area 2D colloidal crystals (CCs) using poly­(<i>N</i>-isopropyl­acrylamide) (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 thiol–ene 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

Order–Disorder 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 order–disorder 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 poly­(<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 Wu–Morbidelli 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>_f, of the hydrogel decreases from ∼2.5 to ∼1.8 when the heating temperature increases from 34 to 40 °C. The <i>d</i>_f 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>_f of the hydrogel decreases from ∼2.1 to ∼1.7, 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 poly­(<i>N</i>-isopropylacrylamide) (PNIPAM) microgel and doped with poly­(<i>N</i>-isopropylacrylamide-<i>co</i>-2-acrylamido-phenylboronic acid) (P­(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, P­(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 P­(AAm-3-AAPBA) from P­(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, P­(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 Thiol–Ene 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 thiol–ene 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 poly­(<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 4–5 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 “No-G20” scenario during the preparatory period and the summit period (July–September 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 Thiol–Ene 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 thiol–ene 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 poly­(<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