Stretchable OFET Memories: Tuning the Morphology and the Charge-Trapping Ability of Conjugated Block Copolymers through Soft Segment Branching.

The mechanical properties and structural design flexibility of charge-trapping polymer electrets have led to their widespread use in organic field-effect transistor (OFET) memories. For example, in the electrets of polyfluorene-based conjugated/insulating block copolymers (BCPs), the confined fiberlike polyfluorene nanostructures in the insulating polymer matrix act as effective hole-trapping sites, leading to controllable memory performance through the design of BCPs. However, few studies have reported intrinsically stretchable charge-trapping materials and their memory device applications, and a practical method to correlate the thin-film morphology of BCP electrets with their charge-trapping ability has not yet been developed. In this study, a series of new conjugated/insulating BCPs, poly(9,9-di-n-hexyl-2,7-fluorene)-block-poly(δ-decanolactone)s (PF-b-PDLx, x = 1-3), as stretchable hole-trapping materials are reported. The linear and branched PDL blocks with comparable molecular weights were used to investigate the effect of polymer architecture on morphology and device performance. Moreover, the coverage area of the polyfluorene nanofibers on the BCP films was extracted from atomic force microscopy images, which can be correlated with the trapping density of the polymer electrets. The branched PDL segments not only improve stretchability but also tailor crystallinity and phase separation of the BCPs, thus increasing their charge-trapping ability. The OFET memory device with PF-b-PDL3 as the electret layer exhibited the largest memory window (102 V) and could retain its performance at up to 100% strain. This research highlights the importance of the BCP design for developing stretchable charge-trapping materials.

[Effects of plantation on aggregate distribution and stability of lateritic red soil in south subtropical China]. / 南亚热带人工林种植对赤红壤团聚体分布及稳定性的影响.

We examined the stability of soil aggregates in five typical plantations, i.e., Eucalyptus urophylla × E. grandis plantation, Cunninghamia lanceolata plantation, Pinus massoniana plantation, Mytilaria laosensis plantation and Castanopsis hystrix plantation, in the south subtropical China by the Elliott wet sieving and Le Bissonnais (LB) methods. The results showed that the content of water stability aggregate (WR>0.25) was more than 62.2% after wet sieving. The mean weight diameter (MWD) and geometric mean diameter (GMD) of aggregates were 1.58-3.71 mm and 0.57-2.02 mm, respectively, which were the largest in C. lanceolata plantation and the smallest in E. urophylla × E. grandis plantation. Percentage of aggregate destruction (PAD) of five kinds of plantations ranged from 4.6% to 31.5%. The transfer matrix method was used to evaluate the soil aggregates, with the aggregate stability index (ASI) following the order of C. lanceolata plantation > C. hystrix plantation > M. laosensis plantation > P. massoniana plantation > E. urophylla × E. grandis plantation. Under the three treatments of LB method, the FW treatment was the most destructive to the stability of soil aggregates, indicating that dissipation played a major role in the disintegration of soil aggregates. The WS treatment had the least damage to the aggregates. The effect of slow wetting (SW) treatment was between the fast wetting (FW) and wet stirring (WS). Both the MWD and GMD values followed the order of WS>SW>FW, which gradually decreased with the increases of soil depth. The GMD value of aggregates under FW treatment by LB method of five plantations was significantly positively correlated with ASI, MWD and GMD of wet sieving method, indicating that the traditional wet sieving method had a good correlation with FW treatment and was feasible to determine the stability of soil aggregates in the subtropical red soil. Based on the aggregate stability indices of MWD, GMD, PAD and ASI, C. lanceolata plantation was more conducive to the improvement of soil aggregation level, with more stable soil structure than the other four plantations.

[Characteristics of soil saturated hydraulic conductivity on different positions and their controlling factors of granite collapsing gullies]. / èŠ±å²—å²©å´©å²—ä¸åŒéƒ¨ä½åœŸå£¤é¥±å’Œå¯¼æ°´çŽ‡ç‰¹å¾åŠå ¶å½±å“å› ç´ .

Collapsing gully is a common phenomenon of hydraulic-gravity combined soil erosion in granite hilly area of south China. The study aimed to explore the relationship between soil hydraulics pro-perties and erosion mechanism and the intrinsic controlling factors. The active, semi-stable, and stable types of granite collapsing gullies in southeastern Guangxi were selected to examine the spatial variation of soil saturated hydraulic conductivity and identify the influencing factors. Main results were as follows: 1) Soil saturated hydraulic conductivity of collapsing gullies fluctuated on different positions, with the bottom of collapsing wall showing the minimum value, the top of colluvial deposit showing the maximum, and followed by the top of alluvial fan. 2) All the models being selected to model the soil saturated hydraulic conductivity, including Cosby, Compbell, Julià, and Hypre, performed poor. 3) Results of correlation analysis showed that soil saturated hydraulic conductivity was negatively correlated with capillary porosity and clay content, and positively correlated with non-capillary porosity and sand content. 4) Results of path analysis showed that sand content was the most influencing factor in controlling soil saturated hydraulic conductivity of collapsing gullies, followed by non-capillary porosity and soil bulk density, where sand content and non-capillary porosity exerted a positive effect and bulk density exerted a negative one. Our findings will provide theoretical basis for the mechanistic understanding and prevention of collapsing gullies erosion.

Facile Fabrication of Stretchable Touch-Responsive Perovskite Light-Emitting Diodes Using Robust Stretchable Composite Electrodes.

Perovskite light-emitting diode (PeLED) has been vigorously developed in recent years. As it has demonstrated good performance on the rigid substrates, the next important direction of PeLED is its integration with stretchable components to realize stretchable, responsive device. Here, we describe a facile fabrication of stretchable perovskite light-emissive touch-responsive devices (PeLETDs) by utilizing highly transparent and conductive polyurethane/silver nanowires (PU/AgNWs) as the electrode. Meanwhile, a stretchable tricomposite perovskite emissive layer was developed by blending a small amount of poly(ethylene oxide) (PEO) and poly(vinylpyrrolidone) (PVP) with CsPbBr3. Additionally, a thin PVP layer was introduced at the bottom of the emissive layer. On one hand, it can further improve the morphology of the emissive layer; on the other hand, it can serve as an electron-injection barrier to reduce the high nonradiative recombination at the corresponding interface. Further, to fulfill the responsive function of the fabricated PeLEDs, a poly(ethylene terephthalate) (PET) spacer with a 100 µm thickness was inserted between the top electrode and the emissive layer. A stretchable PeLETD is finally demonstrated to possess a low turn-on voltage of 2 V with a brightness of 380.5 cd m-2 at 7.5 V and can sustain 30% uniaxial strain with a small luminance variation of 24%. More interestingly, our stretchable PeLETD exhibited high stability, which could be well touch responsivity, where the luminance is on/off switched for 300 cycles by repeatedly applying pressure.

Light Down-Converter Based on Luminescent Nanofibers from the Blending of Conjugated Rod-Coil Block Copolymers and Perovskite through Electrospinning.

We demonstrated a novel strategy for the preparation of light down-converter by combining rod-coil block copolymers with perovskite quantum dots (QDs) through electrospinning. Reports have shown that polymer deformability can be enhanced by incorporating a soft segment and controlled by varying the rod/coil ratio. Therefore, we first synthesized the rod-coil block copolymer through the click reaction of polyfluorene (PF) and poly(n-butyl acrylate) (PBA). Next, the CsPbBr3@PF8k-b-PBA12k composite fibers were fabricated by blending perovskite through electrospinning. Optical spectral evidence demonstrated the success of the strategy, as light down-converters were prepared through the controlled variance of QD/polymer ratios to achieve tunable color and stretchability. This result reveals the potential of using rod-coil block copolymers to fabricate color-tunable perovskite light down-converters.

Multiple Scattering from Electrospun Nanofibers with Embedded Silver Nanoparticles of Tunable Shape for Random Lasers and White-Light-Emitting Diodes.

Random lasers (RLs) are convenient, tunable, and widely applicable. However, the influence of fluorescence lifetime on the scattering and nanofiber distribution of nanofibers with various shapes of silver nanoparticles (Ag NPs) embedded within is unclear. We prepared poly(vinyl alcohol) (PVA) nanofibers with Ag NPs through electrospinning (ES) and pyrromethene 597 dye doping. We determined the influences of the particles on scattering enhancement and localized surface plasmon resonance (LSPR) in RLs. The distinct scattering rates and LSPR can be used to control optical properties for sensing devices and other applications. Compared with traditional films, the threshold of the nanofibers with Ag NPs is 35% lower. In addition to improved matching between the LSPR and emission spectra, enhanced coupling of the electric field with nonradiative energy amplifies the radiative emission. Furthermore, the luminescence lifetime shortened by increasing the scattering rate. An excessive scattering rate may accelerate radiative recombination and convert some recombination into nonradiative recombination to produce a more sensitive device. Finally, we applied the prepared nanofibers to a backlight display and fabricated a white-light-emitting diode (LED) with a distinct thickness of nanofibers. The fabricated device is suitable for application in other LEDs and RL devices.

Facile 3D Boron Nitride Integrated Electrospun Nanofibrous Membranes for Purging Organic Pollutants.

Elegant integration of three-dimensional (3D) boron nitride (BN) into the porous structure of a polymer nanofiber (NF) membrane system results in a surface with enhanced absorption capacity for removal. Various BN-based applications were designed and developed successfully, but BN-based absorption systems remain relatively unexplored. To develop a reusable absorption strategy with high removal efficiency, we used a composite of 3D BN and polyacrylonitrile (PAN) to prepare a NF membrane with a porous structure by using electrospinning and spray techniques (BN-PAN ES NFs). The removal efficiency of the 3D BN NF membrane was higher than that of a pure carbon NF membrane. Water pollutants, such as the dyes Congo red (CR), basic yellow 1 (BY), and rhodamine B (Rh B), were tested, and the absorption ratios were 46%, 53%, and 45%, respectively. Furthermore, the aforementioned dyes and pollutants can be completely eliminated and removed from water by heating because of the high heat resistance of 3D BN. The membrane can be recycled and reused at least 10 times. These results indicate that BN-PAN ES NFs have can be used in water purification and treatment for absorption applications, and that they can be reused after heat treatment.

Facile Preparation of Cu/Ag Core/Shell Electrospun Nanofibers as Highly Stable and Flexible Transparent Conductive Electrodes for Optoelectronic Devices.

Novel transparent conductive electrodes (TCEs) with copper (Cu)/silver (Ag) core/shell nanofibers (NFs) containing random, aligned, and crossed structures were prepared using a combination of electrospinning (ES) and chemical reduction. The ES process was used to prepare continuous copper nanofibers (Cu-NFs), which were used as core materials and were then immersed in silver ink (Ag ink) to form a protective layer of Ag to protect the Cu-NFs from oxidation. The Ag shell layer protected the Cu-NFs against oxidation and enhanced their conductivity. Such Cu/Ag core/shell webs can be easily transferred on the flexible matrix and can be applied in TCEs. The metal NF webs of different structures exhibited various degrees of conductivity and followed the order random type > crossed type > aligned type; however, the order with respect to transmittance ( T) was inverse. The aligned nanowire networks exhibited a high T of over 80%, and the random ones exhibited a low sheet resistance of less than 102 Ω/sq (the best value is 7.85 Ω/sq). The present study demonstrated that TCEs based on Cu/Ag core/shell NF webs have considerable flexibility, transparency, and conductivity and can be applied in novel flexible light-emitting diode devices and solar cells in the future.

A mechanically robust silver nanowire-polydimethylsiloxane electrode based on facile transfer printing techniques for wearable displays.

Silver nanowire (AgNW) networks have attracted considerable attention as transparent electrodes for emerging flexible optoelectronics. However, the transference of such networks onto diverse arbitrary substrates with high conductivity remains a challenge because of the possibility of detaching and sliding occurring at the interface. Therefore, we developed a water-assisted transfer printing method for the fabrication and transfer of an AgNW-polydimethylsiloxane (PDMS) electrode. This innovative approach exhibits a robust ability for thin film transfer onto arbitrary substrates and has highly controlled and nondestructive characteristics. The obtained electrodes exhibited a high ratio of DC conductivity to optical conductivity of 200, a low sheet resistance of 9 Ω sq-1 at 82%, tensile strain (0% to 50%), and flexibility (bending radius of less than 2 mm) without significant loss of conductivity compared with devices fabricated through conventional methods. Furthermore, we demonstrated a novel textile-based flexible light-emitting electrochemical cell (PLEC) based on the stretchable AgNW-PDMS electrode and buckling concept, thereby realizing highly stretchable PLECs with excellent performance and mechanical robustness. The luminance intensity of the strained device was optimized to 58 cd m-2 at 7 V under 10% linear strain without damaging the electroluminescence properties. Notably, this effective and practical transfer method provides a way to develop electronic nanowire devices with unique configurations and high performances.

Novel stretchable thermochromic transparent heaters designed for smart window defroster applications by spray coating silver nanowire.

A productive and novel method for fabricating stretchable transparent heaters with recognised thermochromic properties using commercially available thermochromic ink (TM-55-blue) and silver nanowire (AgNW)-coated polydimethylsiloxane (PDMS) is proposed. Lower resistance, elevated heat generation, and higher transparencies were the expected essential prerequisites for the fabrication of items such as smart windows and window defrosters. AgNW-coated PDMS (hereafter PH devices) satisfied the essential prerequisites but did not produce sufficient color change. In addition to the appreciable electrical and optical characteristics and mechanical robustness, observable color changes represent a critical factor in effortless temperature monitoring by the heating device. Blending TM-55-blue thermochromic ink with PDMS (PBH device) improves the heating rate and color transformation and promotes the ultralow response time appreciably. More notably, it produces a visible transformation from blue to colorless. Color changes visible to the naked eye, ultralow response time, and heating rate represent valuable features for deploying the PBH devices as window defrosters and in smart window applications.

Water-Resistant Efficient Stretchable Perovskite-Embedded Fiber Membranes for Light-Emitting Diodes.

Cesium lead halide perovskite nanocrystals (NCs) with excellent intrinsic properties have been employed universally in optoelectronic applications but undergo hydrolysis even when exposed to atmospheric moisture. In the present study, composite CsPbX3 (X = Cl, Br, and I) perovskite NCs were encapsulated with stretchable (poly(styrene-butadiene-styrene); SBS) fibers by electrospinning to prepare water-resistant hybrid membranes as multicolor optical active layers. Brightly luminescent and color-tunable hydrophobic fiber membranes (FMs) with perovskite NCs were maintained for longer than 1 h in water. A unique remote FMs packaging approach was used in high-brightness perovskite light-emitting diodes (PeLEDs) for the first time.

Novel Multifunctional Luminescent Electrospun Fluorescent Nanofiber Chemosensor-Filters and Their Versatile Sensing of pH, Temperature, and Metal Ions.

Novel multifunctional fluorescent chemosensors composed of electrospun (ES) nanofibers with high sensitivity toward pH, mercury ions (Hg2+), and temperature were prepared from poly(N-Isopropylacrylamide-co-N-methylolacrylamide-co-rhodamine derivative) (poly(NIPAAm-co-NMA-co-RhBN2AM)) by employing an electrospinning process. NIPAAm and NMA moieties provide hydrophilic and thermo-responsive properties (absorption of Hg2+ in aqueous solutions), and chemical cross-linking sites (stabilization of the fibrous structure in aqueous solutions), respectively. The fluorescent probe, RhBN2AM is highly sensitive toward pH and Hg2+. The synthesis of poly(NIPAAm-co-NMA-co-RhBN2AM) with different compositions was carried on via free-radical polymerization. ES nanofibers prepared from sensory copolymers with a 71.1:28.4:0.5 NIPAAm:NMA:RhBN2AM ratio (P3 ES nanofibers) exhibited significant color change from non-fluorescent to red fluorescence while sensing pH (the λPL, max exhibited a 4.8-fold enhancement) or Hg2+ (at a constant Hg2+ concentration (10-3 M), the λPL, max of P3-fibers exhibited 4.7-fold enhancement), and high reversibility of on/off switchable fluorescence emission at least five times when Hg2+ and ethylenediaminetetraacetic acid (EDTA) were sequentially added. The P3 ES nanofibrous membranes had a higher surface-to-volume ratio to enhance their performance than did the corresponding thin films. In addition, the fluorescence emission of P3 ES nanofibrous membranes exhibited second enhancement above the lower critical solution temperature. Thus, the ES nanofibrous membranes prepared from P3 with on/off switchable capacity and thermo-responsive characteristics can be used as a multifunctional sensory device for specific heavy transition metal (HTM) in aqueous solutions.

Novel highly selective and reversible chemosensors based on dual-ratiometric fluorescent electrospun nanofibers with pH- and Fe(3+)-modulated multicolor fluorescence emission.

Novel dual-ratiometric fluorescent electrospun (ES) nanofibers featuring high sensitivity for pH and ferric ion (Fe(3+)) were prepared using binary blends of poly(2-hydroxyethyl methacrylate-co-N-methylolacrylamide-co-nitrobenzoxadiazolyl derivative) (poly(HEMA-co-NMA-co-NBD)) and a spirolactam rhodamine derivative (SRhBOH) by employing a single-capillary spinneret. The HEMA, NMA, and NBD moieties were designed to exhibit hydrophilic properties, chemical cross-linking, and fluorescence (fluorescence resonance energy transfer (FRET) donor), respectively. The fluorescence emission of SRhBOH was highly selective for pH and Fe(3+); when SRhBOH detected acidic media and Fe(3+), the spirocyclic form of SRhBOH, which is nonfluorescent, was transformed into the opened cyclic form and exhibited strong fluorescence emission. The emission colors of ES nanofibers in acidic or Fe(3+) aqueous solutions changed from green to red because of FRET from NBD (donor) to SRhBOH (acceptor). The off/on switching of the FRET process was modulated by adjusting the SRhBOH blending ratio, pH, and Fe(3+) concentration. Poly(HEMA-co-NMA-co-NBD) ES fibers blended with 20% SRhBOH showed high sensitivity in sensing Fe(3+) and pH because of the substantial 57 nm red shift in emission as well as substantial reversible dual photoluminescence. The prepared FRET-based dual-ratiometric fluorescent ES nanofibrous membranes can be used as "naked eye" sensors and have potential for application in multifunctional environment sensing devices.

Amplification of plasmid DNA bound on soil colloidal particles and clay minerals by the polymerase chain reaction.

Polymerase chain reaction (PCR) was used to amplify a 600-base pair (bp) sequence of plasmid pGEX-2T DNA bound on soil colloidal particles from Brown soil (Alfisol) and Red soil (Ultisol), and three different minerals (goethite, kaolinite, montmorillonite). DNA bound on soil colloids, kaolinite, and montmorillonite was not amplified when the complexes were used directly but amplification occurred when the soil colloid or kaolinite-DNA complex was diluted, 10- and 20-fold. The montmorillonite-DNA complex required at least 100-fold dilution before amplification could be detected. DNA bound on goethite was amplified irrespective of whether the complex was used directly, or diluted 10- and 20-fold. The amplification of mineral-bound plasmid DNA by PCR is, therefore, markedly influenced by the type and concentration of minerals used. This information is of fundamental importance to soil molecular microbial ecology with particular reference to monitoring the fate of genetically engineered microorganisms and their recombinant DNA in soil environments.

[Inhibited proliferation and expression of human nasopharyngeal carcinoma line induced by celecoxib in vitro].

OBJECTIVE: To study the effects of celecoxib on the cell proliferation and expression of vascular endothelial growth factor (VEGF) in human nasopharyngeal carcinoma line. METHODS: 3-[ 4,5-dimethylthiazol-2-yl]-2, 5-diphenyl tetrazolium bromide (MTT) test was used to investigate the cell proliferation. Flow cytometry (FCM) was used to analyze the cell cycle arrest. Immunocytochemistry technique was to observe the expression of VEGF. RESULTS: Celecoxib inhibited the growth of nasopharyngeal carcinoma line, the cell number of G0/G1 phase increased from 62.13% to 91.35%, and the cell number of G2/M and S phase decreased from 21.59% to 3.56% and from 16.28% to 5.01%, respectively, cell cycle progression was arrested at G1/S phase. Celecoxib decreased the positive expression of VEGF in HNE-1 cells. CONCLUSIONS: Celecoxib inhibited the proliferation of nasopharyngeal carcinoma significantly and the expression of VEGF.