Large hydrophobic monomers stearyl methacrylate (C18) and dococyl acrylate (C22) could be copolymerized with the hydrophilic monomer acrylamide in a micellar solution of sodium dodecyl sulfate (SDS). ...This was achieved by the addition of salt (NaCl) into the reaction solution. Salt leads to micellar growth and, hence, solubilization of the hydrophobes within the SDS micelles. The hydrogels thus obtained without a chemical cross-linker exhibit unique properties due to the strong hydrophobic interactions. They can only be dissolved in SDS solutions demonstrating the physical nature of cross-links. Results of dynamic light scattering, rheological and mechanical measurements show that the hydrophobic associations between the blocks of C18 or C22 units prevent water solubility and flow, while the dynamic nature of the junction zones provides homogeneity and self-healing properties together with a high degree of toughness. When fractured, the hydrogels formed using C18 associations can be repaired by bringing together fractured surfaces to self-heal at room temperature, after which, they again exhibit the original extensibility of about 3600%. The existence of free, nonassociated blocks in C18 hydrogels is accounted for their high self-healing efficiencies.
π-Conjugated small molecules, oligomers, and macromolecules are being used in the fabrication of a wide variety of organic electronic devices such as organic field-effect transistors (OFETs), organic ...photovoltaic (OPV) devices, and organic light-emitting diodes (OLEDs). Efficient syntheses involving fewer steps, fewer toxic reagents, and highly reactive compounds are needed to lower the cost of materials in a manner that is fundamentally more eco-friendly. Additionally, synthetic approaches for π-conjugated materials with more functional group tolerance are desirable to expand the range of properties that can be realized in such materials. Developing new synthetic routes to materials can both broaden the scope of science that can be explored and increase the probability that interesting materials can be developed in an economically viable manner for inclusion in consumer products. One such synthetic strategy that can impact all of these issues is carbon–hydrogen bond activation and subsequent carbon–carbon bond formation (C–H functionalization). While the C–H functionalizations represented by direct arylation-based methods are not as developed as the widely used Stille and Suzuki methods at this stage, they allow for the use of readily accessible halogenated aromatic substances and can negate the need for toxic organotin reagents. They also hold promise of allowing for the synthesis of previously inaccessible materials. In this Perspective, our goal is to provide an overview of the current status in this challenging field by highlighting (1) the history of preparing π-conjugated small molecules and macromolecules via cross-coupling reactions, (2) advances in preparation of versatile π-conjugated small molecules and macromolecules via transition-metal-catalyzed direct arylation, and (3) the scope, limitations, and challenges for materials science.
Recently, the benzodithiophene- (BDT-) based polymers with conjugated side groups attracted considerable attention due to their superior properties in polymer solar cells (PSCs), so the investigation ...of the side chain effects on the photovoltaic properties of this type of polymers is an interesting and important topic for molecular design. Herein, three conjugated polymers based on BDT and thieno3,4-bthiophene units with furan, thiophene and selenophene as side groups, named as PBDTTT-EFF, PBDTTT-EFT, and PBDTTT-EFS, were synthesized and applied in polymer solar cells. The polymers were characterized in parallel by absorption spectroscopy, thermogravimetric analysis (TGA), density functional theory (DFT), ultraviolet photoemission spectroscopy (UPS), X-ray diffraction (XRD), and photovoltaic measurements. The results show that the dihedral angles between the BDT and conjugated side groups play important roles in affecting the absorption bands, HOMO levels, crystallinities, and aggregation sizes of the polymers. The photovoltaic results indicate that PBDTTT-EFT and PBDTTT-EFS show similar photovoltaic characteristics in device, and PCEs of 9.0% and 8.78% were obtained, respectively. The device of PBDTTT-EFF shows a V oc of 0.69 V and a J sc of 11.77 mA/cm2, which are lower than those in the devices based on the other two polymers. Overall, this work suggests that the photovoltaic properties of the BDT-based polymers can be effectively tuned by introducing conjugated side groups with varied steric hindrance.
•The mineralogical composition of the suspended sediment exhibits a high degree of spatial variability.•SPM concentrations are very high near the source of the meltwater plume and contain a high ...content of mineral particles, particularly inorganic matter, with concentrations ranging from 82.5% to 97.9% of TSM.•The particle size distribution (PSD) reflects the mineral composition of the suspended sediment.
Particle size distribution (PSD) and concentration of mineral-suspended sediment released from melting glaciers are important factors affecting the local marine ecosystem, e.g. affecting the light availability in water columns, thus changing underwater light climate for photosynthetic organisms. We examined the characteristics of various samples of natural mineral assemblages suspended in different glacial bays in Hornsund and Kongsfjord at Spitsbergen. The concentrations of the total mass of particles (TSM) in suspended sediment as well as particular organic matter (POM) and particular inorganic matter mass (PIM) together with mineralogical composition and particular size distribution (PSD) were determined.
In this study, we investigated the PSD properties and variability in the front of different tidewater glaciers based, laser diffractometer measurements (LISST-100x), and XRD – techniques to obtain the mineralogical composition of the particles. The sampled sites are under the strong influence of freshwater discharge from the glacier. At each station, inorganic particulate matter contributed up to 98% to total suspended matter with the particle concentration of the particle reaches up to 111 mg/l with mean surface PSD slopes ranging from 3.24 to 3.85. The result provides valuable baseline information on the observed range of variability of the size of suspended particles due to glacial runoff and the presence of particles of different mineral origin in the glacial bays.
In the past, polynomial particular solutions have been obtained for certain types of partial differential operators without convection terms. In this paper, a closed-form particular solution for more ...general partial differential operators with constant coefficients has been derived for polynomial basis functions. The newly derived particular solution is further coupled with the method of particular solutions (MPS) for numerically solving a large class of elliptic partial differential equations. In contrast to the use of Chebyshev polynomial basis functions, the proposed approach is more flexible in selecting the collocation points inside the domain. The polynomial basis functions are well-known for yielding ill-conditioned systems when their order becomes large. The multiple scale technique is applied to circumvent the difficulty of ill-conditioning problem. Five numerical examples are presented to demonstrate the effectiveness of the proposed algorithm.
The research on the polymer-based solar cells (PSCs) has attracted an increasing amount of attention in recent years because PSCs pose potential advantages over mainstream inorganic-based solar ...cells, such as significantly reduced material/fabrication costs, flexible substrates, and light weight of finished solar cells. The research community has made great progress in the field of bulk heterojunction (BHJ) polymer solar cells since its inception in 1995. The power conversion efficiency (PCE), a key parameter to assess the performance of solar cells, has increased from 1% in the 1990s to over 8% just recently. These great advances are mainly fueled by the development of conjugated polymers used as the electron-donating materials in BHJ solar cells. In this Perspective, we first briefly review the progress on the design of conjugated polymers for polymer solar cells in the past 16 years. Since a conjugated polymer can be arbitrarily divided into three constituting componentsthe conjugated backbone, the side chains, and the substituentswe then focus on the rational design of conjugated polymers by separately discussing the influence of each component on the physical and photovoltaic (PV) properties of these polymers. Special attention is paid to the design of donor–acceptor type low-band-gap polymers because this approach is prevailing in the literature with its unique features. In doing so, we strive to extract useful rules for the rational design of conjugated polymers with predictable properties. We conclude by proposing future research opportunities to achieve even higher PCEs for PSCs.
After the Global Financial Crisis, a controversial rush to fiscal austerity followed in many countries. Yet research on the effects of austerity on macroeconomic aggregates was and still is ...unsettled, mired by the difficulty of identifying multipliers from observational data. This article, reconciles seemingly disparate estimates of multipliers within a unified and state-contingent framework. We achieve identification of causal effects with new propensity-score based methods for time series data. Using this novel approach, we show that austerity is always a drag on growth, and especially so in depressed economies: a 1% of GDP fiscal consolidation translates into a loss of 3.5% of real GDP over five years when implemented in a slump, rather than just 1.8% in a boom.
Self-healing polymeric materials with branched architectures and reversible cross-linking functionalities at the periphery of branches were synthesized by atom transfer radical polymerization (ATRP). ...Poly(n-butyl acrylate) grafted star polymers were prepared by chain extension ATRP from cross-linked cores comprised of poly(ethylene glycol diacrylate). These polymers were further used as macroinitiators for the consecutive chain extension ATRP of bis(2-methacryloyloxyethyl disulfide) (DSDMA), in which way disulfide reversible cross-links (SS) were introduced at the branch peripheries. The SS cross-linked polymers were then cleaved under reducing conditions to form thiol (SH)-functionalized soluble star polymers. The SH-functionalized star polymer solutions were deposited on silicon wafer substrates and converted to insoluble SS re-cross-linked films via oxidation. The self-healing of prepared polymer films was studied by continuous atomic force microscopy (AFM) imaging of cuts micromachined with the AFM tip and by optical microscopy. The re-cross-linked star polymer (X3) showed a rapid spontaneous self-healing behavior, with the extent of healing dependent on the initial film thickness and the width of the cut. The self-healing behavior observed for this sample was attributed to the regeneration of SS bonds via thiol–disulfide exchange reactions. This study demonstrated the suitability of grafted multiarm polymer architectures as building blocks of self-healing polymeric materials and pointed to the importance of low intrinsic viscosity of material and high accessibility of functional groups responsible for healing.
Exposure to fine particular matter (≤2.5 μM, PM2.5) contributes to increased risk of obesity and type 2 diabetes. Hydroxytyrosol (HT), a simple polyphenol found in virgin olive oil, is considered to ...be beneficial for cardiovascular and metabolic disorders. The current study determined whether HT could improve PM2.5-induced adiposity and insulin resistance (IR), and explored the underlying mechanisms. Fifteen adult female C57BL/6j mice on a chow diet were randomly divided into three groups receiving (1) sterile PBS, (2) PM2.5 suspended in sterile PBS (1 mg/mL) and (3) PM2.5+HT (50 mg/kg/day). PM2.5/PBS exposure was administered by oropharynx instillation every other day and HT supplementation was achieved by gavage every day. Four-week PM2.5 exposure did not affect body weight, but significantly increased visceral fat mass. The abdominal adiposity coincided with adipocyte hypertrophy and proliferation in visceral white adipose tissue (WAT), as well as decreased metabolic activity in brown adipose tissue and subcutaneous WAT. PM2.5 enhanced the oxidative stress by diminishing antioxidant enzyme activities in liver and serum, whereas contents of 4-hydroxynonenal (4-HNE), malondialdehyde (MDA) levels in liver and serum were elevated. These changes were accompanied by macrophage infiltration and activation of NF-κB pathway in the liver. Moreover, PM2.5 exposure led to glucose intolerance and insulin insensitivity, impaired hepatic glycogenesis, and decreased insulin-stimulated Akt phosphorylation in peripheral tissues. Importantly, HT treatment prevented PM2.5-induced visceral adipogenesis, oxidative stress, hepatic inflammation and NF-κB activation, systemic and peripheral IR. In vitro, after HepG2 cells were incubated with PM2.5 (0, 5, 25, 50, 100 and 200 μg/mL), reduced glutathione depletion and 4-HNE, 8-hydroxy-2'-deoxyguanosine, MDA increment in a dose-dependent manner were observed; likewise, insulin-stimulated glucose uptake decreased in a dose-dependent manner. Further, with antioxidant NAC and NF-κB inhibitor PDTC, we confirmed that HT attenuated PM2.5-induced IR through restraining NF-κB activation evoked by oxidative stress. In addition, HT could expand gut microbiota richness, reduce pathogenic bacteria and accommodate the microbial architecture in PM2.5-exposed mice, which were correlated with parameters of adiposity, oxidative stress and glycometabolism. HT could effectively correct imbalanced oxidative stress triggered by PM2.5, in turn ameliorated NF-κB pathway and insulin signaling. Gut microbiota may mediate the actions of HT.
A schematic illustration of how HT interfered with PM2.5-induced oxidative stress and metabolic disorders in vivo and in vitro. vWAT, visceral white adipose tissue; scWAT, subcutaneous WAT; BAT, brown adipose tissue; PPARγ, peroxisome proliferator-activated receptor gamma; C/EBPα, CCAAT/enhancer-binding protein alpha; UCP1, uncoupling protein 1; COX2, cyclooxygenase 2; IL-1β, interleukin 1beta; TNFα, tumor necrosis factor alpha; GSK3β, glycogen synthase kinase 3β; GS, glycogen synthase; ↑indicates increase, ↓indicates decrease. Display omitted
•Hydroxytyrosol alleviates PM2.5-induced visceral adiposity, oxidative stress, insulin resistance (IR), and gut dysbiosis.•Hydroxytyrosol mitigates hepatic IR through inhibiting NF-κB activation derived from oxidative stress induced by PM2.5.•Modulation of gut microbiota may mediate the pharmacologic actions of orally administrated Hydroxytyrosol.
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