Lignin is an attractive renewable reinforcing agent for polyolefins and also a promising low-cost antioxidant for polymers. It, however, exhibits poor compatibility with nonpolar polymers. In this work, alkali lignin was freeze-dried to achieve sheet-like morphology and then incorporated into polypropylene (PP) by melt compounding. Owing to the significantly increased interfacial area and improved dispersion, with the addition of only 2 wt % freeze-dried lignin, the PP/ lignin composites show much enhanced tensile mechanical properties, including a moderately improved Young's modulus and almost doubled elongation at break compared with those of neat PP. The enhancements brought by the sheet-like lignin are far more impressive than those achieved with the same amount of as-received lignin. The composites with the freezedried lignin also have rough fractured surfaces with fiber pull-out near the interface, revealing a significant toughening effect of the lignin, which can be attributed to the crazing near the interface, and enhanced relaxation in PP-lignin interphase as evidenced by the reduced T g . Furthermore, the large interfacial area also drastically improves the antioxidant effect of lignin, greatly slowing the UV-induced and thermo-oxidative degradation of PP. After 2 weeks of intense UV exposure, neat PP becomes very brittle with its yield strain reduced to about 37% of its original value, whereas the yield strain of the composite with 2 wt % sheet-like lignin is almost unchanged, demonstrating the excellent free-radical scavenger effect of the lignin.

Well‐defined cyclic poly(acrylic acid) (PAA) has been successfully prepared based on the direct click cyclization. The linear poly(tert‐butyl acrylate) (PtBA) with azide and TMS‐protected alkyne group forms cyclic chain directly by the copper(I)‐catalyzed click cyclization without any deprotection steps. Cyclic PAA is synthesized by the hydrolysis of cyclic PtBA. The present synthetic strategy provides a simple and efficient method to synthesize cyclic polyelectrolyte and can be applied to other polymer systems.

In recent years, metal‐halide perovskite quantum dots (QDs) have been broadly applied in optoelectronic fields due to their fascinating characteristics, such as high photoluminescence quantum yields, tunable bandgaps, and low‐cost solution processing. Here, a facile ligand‐exchange strategy is employed for the fabrication of CsPbBr3 QDs capped with di‐dodecyl dimethyl ammonium bromide. It is demonstrated that the treated QDs' film becomes more compact with higher electron mobility and shorter lifetime. Besides, a reduced conduction band minimum value (0.28 eV) of perovskite QDs' film provides an efficient electron injection to them from ZnO nanoparticles. Through using the well‐passivated QDs' film, electroluminescence QD light‐emitting diode (QLED) devices with an indium tin oxide/ZnO/CsPbBr3 QDs/MoO3/4, 4′‐bis(carbazole‐9‐yl)biphenyl/Al inverted sandwich structure are achieved. The as‐prepared QLED device exhibits a maximum current efficiency of 0.62 cd A−1 and an external quantum efficiency of 0.58%, which is nearly nine times higher than that of the device based on unmodified QDs. More importantly, the stability testing results demonstrate that the QLED can be operated for more than 20 min under ambient conditions without any encapsulation. This provides an alternative route for highly efficient perovskite‐based LED with inverted sandwich structures.

Interfacial water structure at charged surfaces plays a key role in many physical, chemical, biological, environmental, and industrial processes. Understanding the release of interfacial water from the charged solid surfaces during dehydration process may provide insights into the mechanism of protein folding and the nature of weak molecular interactions. In this work, sum frequency generation vibrational spectroscopy (SFG-VS), supplemented by quartz crystal microbalance (QCM) measurements, has been applied to study the interfacial water structure at polyelectrolyte covered surfaces. Poly[2-(dimethylamino)ethyl methacrylate] (PDMAEMA) chains are grafted on solid surfaces to investigate the change of interfacial water structure with varying surface charge density induced by tuning the solution pH. At pH ≤ 7.1, SFG-VS intensity is linear to the loss of mass of interfacial water caused by the dehydration of PDMAEMA chains, and no reorientation of the strongly bonded water molecules is observed in the light of χ(ppp)/χ(ssp) ratio. χ((3)) contribution to SFG signal is deduced based on the combination of SFG and QCM results. It is the first direct experimental evidence to reveal that the χ((3)) has a negligible contribution to SFG signal of the interfacial water at a charged polymer surface.

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Layered double hydroxide with exchangeable interlayer anions are considered promising electroactive materials for renewable energy technologies. However, the limited exposure of active sites and poor electrical conductivity of hydroxide powder restrict its application. Herein, bifunctional integrated electrode with a 3D hierarchical carbon framework decorated by nickel iron-layered double hydroxides (NiFe-LDH) is developed. A conductive carbon nanowire array is introduced not only to provide enough anchoring sites for the hydroxide, but also affords a continuous pathway for electron transport throughout the entire electrode. The 3D integrated architecture of NiFe-hydroxide and hierarchical carbon framework possesses several beneficial effects including large electrochemical active surfaces, fast electron/mass transport, and enhanced mechanical stability. The as-prepared electrode affords a current density of 10 mA cm −2 at a low overpotential of 269 mV for oxygen evolution reaction (OER) in 1 M of KOH. It also offers excellent stability with negligible current decline even after 2000 cycles. Besides, density functional theory calculations revealed that the (110) surface of NiFe-LDH is more active than the (003) surface for OER. Furthermore, the electrode possesses promising application prospects in alkaline battery-supercapacitor hybrid devices with a capacity of 178.8 mAh g −1 (capacitance of 1609.6 F g −1 ) at a current density of 0.2 A g −1 . The viability of the as-prepared bifunctional Nanotechnology Nanotechnology 30 (2019) 325402 (12pp)

We have investigated the influence of number of arms on chain interpenetration in the growth of star poly[2-(dimethylamino)ethyl methacrylate] (PDEM)/star poly(acrylic acid) (PAA) multilayers using a quartz crystal microbalance with dissipation (QCM-D). The oscillations in the changes of dissipation and frequency reflect the chain interpenetration and the variation of the mass of multilayer, respectively. The QCM-D results demonstrate that the growth of multilayers has two different mechanisms in terms of chain interpenetration. That is, the arm chains of star PDEM insert into a predeposited PAA layer to form a swollen multilayer, but the complex of star PAA with predeposited star PDEM is an "octopus-like" structure forming a dense multilayer. The transition between these two penetration modes is controlled by the number of arms in the star polyelectrolytes. As the number of arms of either PAA or PDEM increases, it becomes more difficult for star PDEM to penetrate into the PAA layer, but star PAA can more easily penetrate into the PDEM layer. According to atomic force microscopy and water contact angle measurements, all eight-bilayer multilayer surfaces have similar roughness values, and the surface wettability of the multilayers is dominated by the outermost PDEM layer.