Synthesis of poly[methyl(3,3,3-trifluoropropyl)siloxane]-b-poly(ethylene oxide) block copolymers

一系列新 amphiphilic poly [甲基(3,3,3-trifluoropropyl ) siloxane ]-b-poly(ethylene 氧化物)(PMTFPS-b-PEO ) 把钓饵轻轻放进水里有到吸水的片断的恐水病的片断的不同比率的锁共聚物被联合结束功能的 PMTFPS 和 PEO 人聚合物的反应准备。共聚物被显示由象胶化浸透层析(GPC ) 和 1 H-nudear 磁性的回声(1 H-NMR ) 。

Experimental study on discharge coefficient of a gear-shaped weir

This study focused on hydraulic characteristics around a gear-shaped weir in a straight channel. Systematic experiments were carried out for weirs with two different gear heights and eight groups of geometrical parameters. The impacts of various geometrical parameters of gear-shaped weirs on the discharge capacity were investigated. The following conclusions are drawn from the experimental study:(1) The discharge coefficient(m_c) was influenced by the size of the gear: at a constant discharge, the weir with larger values of a/b(a is the width of the gear, and b is the width between the two neighboring gears) and a/c(c is the height of the gear) had a smaller value of m_c. The discharge capacity of the gear-shaped weir was influenced by the water depth in the weir.(2) For type C1 with a gear height of 0.01 m, when the discharge was less than 60m^3/h and H_1=P < 1.0(H_1 is the water depth at the low weir crest, and P is the weir height), m_c significantly increased with the discharge and H_1=P; with further increases of the discharge and H_1=P, m_cshowed insignificant decreases and fluctuated within small ranges. For type C2 with a gear height of 0.02 m, when the discharge was less than 60m^3/h and H_1=P < 1.0, m_csignificantly increased with the discharge and H_1=P; when the discharge was larger than 60m^3/h and H_1=P > 1.0, m_c slowly decreased with the increases of the discharge and H_1=P for a=b 1.0 and a=c 1.0, and slowly increased with the discharge and H_1=P for a=b > 1.0 and a=c > 1.0.(3) A formula of m_cfor gear-shaped weirs was established based on the principle of weir flow, with consideration of the water depth in the weir, the weir height and width, and the height of the gear.

Correction: The Cymbidium genome reveals the evolution of unique morphological traits

After online publication of the article 1 the author noticed minor typo in Fig.4c.CeSEP1/2/3/4 should be read as CeSEP1/3/4.Revised figure supplied during the proof correction was inadvertently not reproduced in the final version.In addition,the affiliation numbers of the authors revised in the original article during proof correction,but not reflected in the title page in Supplementary Information.

Impacts of water surface area of watershed on design flood

In order to analyze the impact of the water surface area of a watershed on the design flood, the watershed was classified into a land watershed and a water surface watershed for flood flow calculation at the same time interval. Then, the design flood of the whole watershed was obtained by adding the two flood flows together. Using this method, we calculated design floods with different water surface areas of three reservoirs and analyzed the impact of water surface area on the flood volume and peak flow. The results indicate that larger water surface areas lead to greater impacts on the flood volume and peak flow. For the same watershed area, the impact of water surface area on the flood volume and peak flow is positively proportional to the flood frequency, i.e., the higher the frequency, the greater the impact becomes.

Scanning transmission electron microscopy: A review of high angle annular dark field and annular bright field imaging and applications in lithium-ion batteries

Scanning transmission electron microscopy（STEM） has been shown as powerful tools for material characterization,especially after the appearance of aberration-corrector which greatly enhances the resolution of STEM. High angle annular dark field（HAADF） and annular bright field（ABF） imaging of the aberration-corrected STEM are widely used due to their high-resolution capabilities and easily interpretable image contrasts. However, HAADF mode of the STEM is still limited in detecting light elements due to the weak electron-scattering power. ABF mode of the STEM could detect light and heavy elements simultaneously, providing unprecedented opportunities for probing unknown structures of materials. Atomiclevel structure investigation of materials has been achieved by means of these imaging modes, which is invaluable in many fields for either improving properties of materials or developing new materials. This paper aims to provide a introduction of HAADF and ABF imaging techniques and reviews their applications in characterization of cathode materials, study of electrochemical reaction mechanisms, and exploring the effective design of lithium-ion batteries（LIBs）. The future prospects of the STEM are also discussed.

The Cymbidium genome reveals the evolution of unique morphological traits

The marvelously diverse Orchidaceae constitutes the largest family of angiosperms.The genus Cymbidium in Orchidaceae is well known for its unique vegetation,floral morphology,and flower scent traits.Here,a chromosomescale assembly of the genome of Cymbidium ensifolium(Jianlan)is presented.Comparative genomic analysis showed that C.ensifolium has experienced two whole-genome duplication(WGD)events,the most recent of which was shared by all orchids,while the older event was the t event shared by most monocots.The results of MADS-box genes analysis provided support for establishing a unique gene model of orchid flower development regulation,and flower shape mutations in C.ensifolium were shown to be associated with the abnormal expression of MADS-box genes.The most abundant floral scent components identi fied included methyl jasmonate,acacia alcohol and linalool,and the genes involved in the floral scent component network of C.ensifolium were determined.Furthermore,the decreased expression of photosynthesis-antennae and photosynthesis metabolic pathway genes in leaves was shown to result in colorful striped leaves,while the increased expression of MADS-box genes in leaves led to perianth-like leaves.Our results provide fundamental insights into orchid evolution and diversi fication.

Continuously Doping Bi_(2)Sr_(2)CaCu_(2)O_(8+δ)into Electron-Doped Superconductor by CaH_(2)Annealing Method

As a typical hole-doped cuprate superconductor,Bi_(2)Sr_(2)CaCu_(2)O_(8+δ)(Bi2212)carrier doping is mostly determined by its oxygen content.Traditional doping methods can regulate its doping level within the range of hole doping.Here we report the first application of CaH_(2)annealing method in regulating the doping level of Bi2212.By continuously controlling the anneal time,a series of differently doped samples can be obtained.The combined experimental results of x-ray diffraction,scanning transmission electron microscopy,resistance and Hall measurements demonstrate that the CaH_(2)induced topochemical reaction can effectively change the oxygen content of Bi2212 within a very wide range,even switching from hole doping to electron doping.We also found evidence of a low-T_c superconducting phase in the electron doping side.

Atomic-scale structural evolution of electrode materials in Li-ion batteries:a review

Owing to the high spatial resolution at the atomic scale,the transmission electron microscopy(TEM)or scanning transmission electron microscopy is demonstrated as a promising characterization method to unveil the charge storage mechanism of electrode materials in Li-ion batteries.The structural evolution of electrode materials during charge/discharge process can be directly observed by using TEM.The detailed analysis establishes a relationship between the structure of electrode material and battery performance.Herein,we present a brief review of the atomic-scale characterization in Li-ion batteries,including Li(de)insertion mechanism(both cations and anions charge-compensation mechanism),migration of transition metal ions,and surface phase transition.The indepth microscopic analysis reveals the detailed structural characteristics,which influence the properties of LIBs,establish the structure-function relationship,and facilitate the development of Li-ion batteries.

Highly Transparent and Colorless Polyimide Film with Low Dielectric Constant by Introducing Meta-substituted Structure and Trifluoromethyl Groups

An effective design strategy for preparing highly transparent polyimide film with low dielectric constant is presented.The key to the strategy is to simultaneously introduce meta-substituted structure and trifluoromethyl in polymer chains.By using this design strategy,a highly transparent polyimide film with low-k was synthesized from 3,5-diaminobenzotrifluoride(m-TFPDA)and 4,4'-(hexafluoroisopropylidene)diphthalic anhydride(6FDA)through a two-step method.The obtained m-TFPDA/6FDA(CPI)film(~30 pm)possesses high optical transparency(λ_(cutoff)=334 nm,T_(450nm)=85.26%,Haze=0.31)and is close to colorless(L^(*)=96.03,a^(*)=-0.34,b^(*)=2.12,yellow index=3.96).The intrinsic k and dielectric loss value of the film are 2.27 and 0.0013 at 10 kHz,respectively.More importantly,such low dielectric performance could remain stable up to 280℃,and the film shows a low moisture rate(~0.51%),which helps to maintain the low-k property stability in different humid environments.Meanwhile,the film also shows good thermal stability and mechanical properties,with a glass transition temperature(T_(g))of 296℃and the 5 wt%decomposition temperature(T_(d,s%))of 522℃under N_(2).The tensile strength and tensile modulus of the film are 85.1 MPa and 1.96 GPa,respectively.In addition,the film is soluble in common solvents,which allows simple solution processing and low-cost,continuous roll-to-roll processes.This design strategy is beneficial to improving the transparency,lightening yellow color,lowering the dielectric constant and meanwhile maintaining the comprehensive properties of polyimide films,which is mainly due to the introduced meta-substituted and trifluoromethyl structures effectively inhibiting the transfer of charge transfer complex(CTC)effects and increasing the free volume of film.This design strategy could also be extended to other high-performance polymer systems.

纳米尺度非均匀性诱导自更新铁基非晶合金具有优异的长期反应活性（英文）

铁基非晶合金作为亚稳态新型零价铁,具有高活性亚稳态结构、较大的残余应力和高密度低配位点等特性,在催化和废水处理中引起了广泛的关注;但由于腐蚀产物沉淀覆盖活性位点,非晶合金的反应活性随着时间的推移而逐渐降低,导致耐用性差.腐蚀产物沉淀造成长期反应活性降低也是阻碍传统晶态零价铁技术在废水处理领域应用的主要问题之一.本文通过在铁基非晶合金中引入纳米尺度的化学不均匀性,有助于构成局部原电池效应,加速电子在降解过程中的转移,可以有效地克服这一问题.更重要的是,非晶合金中的零价铁被选择性腐蚀/脱合金,导致反应区域局部体积收缩和裂纹形成,裂纹扩展使沉淀腐蚀产物和反应区域自剥落.因此,可以连续提供新的低配位,消除质量传递和反应活性恶化的问题.本文所制备的具有成分不均匀的铁基非晶合金即使在中性溶液中也具有良好的长期反应活性和自更新性能.研究结果不仅为废水处理提供了一种新材料,而且为设计高活性零价铁材料提供了一种新思路.

Fabrication of 6FDA-HFBAPP Polyimide Asymmetric Hollow Fiber Membranes and Their CO2/CH4 Separation Properties

In this work, poly(amide acid) solution, the precursor of polyimide, was synthesized by the reaction of 4,4′-(hexafluoroisopropylidene)diphthalicanhydride and 2,2-bis[4-(4-aminophenoxy)phenyl]-hexafluoropropanane in the solvent of N-methyl-2-pyrrolidone(NMP) and tetrahydrofuran(THF). Then, hollow fiber membranes for high flux gas separation were prepared by dry-jet wet spinning using the precursor solution of poly(amide acid) as the spinning dope and a subsequent imidization process. Silicone rubber was further coated outside the obtained hollow fiber membranes to repair the defects on the denser layer. The effects of internal, external coagulation bath ratios with air gap, and coating solution concentrations on the morphologies, structures, and separation performance of the membranes were studied. Results showed that the sponge-like support layer was formed when the content of NMP was increased from 50% to 90% in the internal coagulation bath. The outer surface of the membrane became denser when the water content in the external coagulation bath increased from 40% to 100%, and the separation coefficient of CO2/CH4 increased by 2 times. This value could reach up to 1.4 when the air gap was 6 cm. With tuning the mass fraction of silicone rubber as 5%, hollow fiber composite membranes with uniform coating layer and an improved separation coefficient of 5.4 could be obtained.

Intermetallic Cu_(5)Zr Clusters Anchored on Hierarchical Nanoporous Copper as Efficient Catalysts for Hydrogen Evolution Reaction

Designing highly active and robust platinum-free electrocatalysts for hydrogen evolution reaction is vital for large-scale and efficient production of hydrogen through electrochemical water splitting.Here,we report nonprecious intermetallic Cu_(5)Zr clusters that are in situ anchored on hierarchical nanoporous copper(NP Cu/Cu_(5)Zr)for efficient hydrogen evolution in alkaline medium.By virtue of hydroxygenated zirconium atoms activating their nearby Cu-Cu bridge sites with appropriate hydrogenbinding energy,the Cu_(5)Zr clusters have a high electrocatalytic activity toward the hydrogen evolution reaction.Associated with unique architecture featured with steady and bicontinuous nanoporous copper skeleton that facilitates electron transfer and electrolyte accessibility,the self-supported monolithic NP Cu/Cu_(5)Zr electrodes boost violent hydrogen gas release,realizing ultrahigh current density of 500mAcm^(-2) at a low potential of-280mV versus reversible hydrogen electrode,with exceptional stability in 1M KOH solution.The electrochemical properties outperform those of state-of-the-art nonprecious metal electrocatalysts and make them promising candidates as electrodes in water splitting devices.

Preparation of High-performance Polyimide Fibers with Wholly Rigid Structures Containing Benzobisoxazole Moieties

In this work, a fully rigid coplanar symmetric heterocyclic unit was introduced into the rigid polyimide macromolecular backbone structure to prepare high-performance polyimide fibers. The novel co-polyimide(co-PI) fibers based on 3,3',4,4'-biphenyltetracarboxylic anhydride(BPDA), p-phenylenediamine(PDA) and 2,6-(4,4'-diaminodiphenyl) benzo[1,2-d:5,4-d'] bisoxazole(PBOA) were fabricated via a twostep wet-spinning method. The effects of benzobisoxazole moiety on spinnability, aggregation structure, and mechanical properties of fibers were systematically discussed. The detailed structural analysis revealed that the well-defined aggregation structures of co-PI fibers were obtained from initial amorphous structure when post hot-drawing temperature was higher than 460 ℃ under proper drawing ratio, and the incorporation PBOA into BPDA-PDA structures produced more compact structural co-PI fiber than homo BPDA-PDA fiber. The BPDA-PDA/PBOA co-PI fibers exhibited optimum tensile strength and modulus of 2.65 and 103 GPa, which increased by 182% and 84% compared to the homo BPDA-PDA fiber, respectively.

A fractional-order multifunctional n-step honeycomb RLC circuit network

研究了一类多功能n阶蜂巢型电阻网络模型,该问题一直未被解决。通过调节电路参数,该网络模型可以转化为含有多种功能的数个不同网络模型,例如一个规则的梯形网络、一个n阶三角形网络,等。我们导出了电阻网络的2个新的等效电阻公式,同时导出了LC网络的等效复阻抗公式,它们都属于分数阶范畴。首先,将一个复杂网络简化为一个简单的等效模型;其次,应用基尔霍夫定律,建立一个分式差分方程模型;再次,采用等效变换方法,给出非线性差分方程的通解。在实际应用中,获得了数个有趣的特殊结论。特别地,讨论分析了一个n阶LC复阻抗网络,发现了许多新的等效复阻抗特性。

Preparation of Low-dielectric Permittivity Polyimide Resins with High Surface Activity from Chemically Bonded Hyperbranched Polysiloxane

Thermosetting resin matrix is the key component of advaneed wave-tra nsparent composites,where low dielectric constant,excellent processability,high thermal stability,as well as good bonding ability are required for resins.Herein,we prepared a series of phenylethynyl terminated polyimide(PI)resins by grafting amine-functi onalized hyperbra nched polysiloxane(HBPSi)to PI chains during the in situ polymerization.The effects of HBPSi on the processability of oligomers,molecular packing,thermal stability,dielectric property and bonding ability to reinforce Kevlar fibers of the cured PI/HBPSi composite resins have been examined in detail.The dielectric constants of the cured composite resins were greatly reduced from 3.29 to 2.19 without compromising its processability and thermal stability.Meanwhile,the 10 wt%HBPSi-containing PI resin demonstrated better bonding ability to reinforce fibers with the in terfacial shear strength(IFSS)of 37.64 MPa,compared with that of neat PI-6 matrix(27.34 MPa),and better adhesion to metal with the lap shear strength of 10.48 MPa,50%higher than that of neat resin PI-6(6.98 MPa).These resultant PI/HBPSi composite resins exhibit excellent comprehensive properties,indicating their great potential as low-dielectric constant resin matrix in radar radome.

Scalable Reaction-spinning of Rigid-rod Upilex-S^(■) Type Polyimide Fiber with an Ultrahigh T_(g)

In the family of polyimide(PI)materials,Upilex-S^(■) film has been a shining star through the research PI materials due to its appealing merits.Unfortunately,the wholly rigid-rod backbone and easily formed skin-core micromorphology and microvoids of Upilex-S~type PI lead to the high difficulty in melt-and wet-spinning fabrication.Herein,we propose a facile and scalable method,reaction-spinning,to fabricate the Upilex-S^(■) type PI fiber,in which the rapid solidification of spinning dope and partial imidization take place simultaneously.Thus,the stability and mechanical strength of as-spun fibers can be improved,and the microvoids in fibers can be greatly reduced in relative to the wet-spun fibers.The resultant Upilex-S^(■) type PI fiber shows higher tensile strength and modulus than most commercial thermal-oxidative polymeric fibers with an ultrahigh glass transition temperature T_(g) of 478℃.Moreover,the WAXS and SAXS results indicate that orthorhombic crystals are formed for Upilex-S^(■) type PI fiber in the post hot-drawing process.Increasing the hot-drawing temperature results in a continuous crystallization and high orientation of PI chains in amorphous phase and perfects the existing lamellar structure,which make a great contribution to the improved mechanical property.

Regulation of morphology and visible light-driven photocatalysis of WO_(3)nanostructures by changing pH

The controlled preparation of hexagonal tungsten trioxide(h-WO_(3))nanostructures was achieved by adjusting the pH of the precursor solution.The effect of the pH on the morphology,elemental composition,and photocatalytic performance of the samples was characterized via X-ray diffraction(XRD),scanning electron microscopy,energy dispersive X-ray spectroscopy,and Raman spectroscopy.Ultraviolet-visible(UV-Vis)spectra were used to evaluate the absorbance and the photocatalytic performance of methylene blue.Photoluminescence(PL),electrochemical impedance spectroscopy,photocurrent response and Brunauer-Emmett-Teller(BET)were used to study the optical properties,electrical performance,and specific surface area of the WO_(3)-nanostructures,respectively.The results indicate that the WO_(3) nanorods prepared at pH=1.0 exhibit the highest photocatalytic performance(87.4%in 1 h),whereas the WO_(3) nanoblocks prepared at p H=3.0 show the lowest.The photocatalytic performance of the one dimensional(1 D)-nanorods can be attributed to their high specific surface area and charge transfer ability.The h-WO_(3) nanostructures were synthesized via a simple method and without a capping agent.They show an excellent photocatalytic performance,which is promising for their application in environment purification.

Construction of Safety and Non-flammable Polyimide Separator Containing Carboxyl Groups for Advanced Fast Charing Lithium-ion Batteries

With the wide applications of lithium-ion batteries(LIBs)in electronic devices and electric vehicles,it is of great importance to improve their safety and electrochemical performance.Herein,soluble polyimides(PI)containing carboxyl groups(―COOH)were synthesized by a simple one-step method and PI separators with sponge-like,interpenetrating porous structures were prepared via non-solvent induced phase separation(NIPS).The obtained PI separators exhibited excellent thermal stability and fire-resistance properties,with the electrolyte uptake of 344%and good dimensional integrity in air at 200℃.The results showed that the lithium-ion transference number of the obtained PI separator could reach 0.48,which was much higher than that of the Celgard-2400 separator(0.38).The Li/LiFePO_(4) half-cell with the PI separator showed excellent cycle capability and high-rate performance with a high capacity of 121.80 mA·h·g^(-1) at 5 C,which was better than that of the cell with the Celgard-2400 separator(54.3 mA·h·g^(-1)),demonstrating the promising applications of this PI separators in LIBs.

Dry-spun Polyimide Fibers with Excellent Thermal Stability,Intrinsic Flame Retardancy and Ultralow Smoke Release

Polymer fiber with an ultrahigh thermal stability,superior flame retardancy and low smoke release during combustion is urgently needed and a crucial challenge for developing advanced fireproof textiles.In this study,a series of high-performance polyimide fibers are synthesized by copolymerizing 4,4'-diaminodiphenylmethane(MDA)into the pyromellitic dianhydride-p-phenylenediamine(PMDA-PDA)backbone for synergistically solving the technical challenge of poor fiber processing ability of these polyimides with a high inherent molecular rigidity.The glass transition temperature(Tg)of resultant fibers with the PDA molar ratio over 50 mol%reaches above 420℃ and their 10 wt%weight loss temperature(T10%)is within 543-633℃.For the typical fiber containing 80 mol%of PDA,the limiting oxygen index(LOI)reaches 39%and exhibits a rapid self-extinguishing performance after deviating from the flame.Meanwhile,this fiber exhibits the minimum heat release rate of 14.1 kW/m^(2) in a long ignition time of 813 s during combustion,revealing its better flame retardancy than the well-known Nomex fiber with a heat release rate of 140.6 kW/m^(2) during the 120 s ignition.Meanwhile,the total smoke production of this polyimide fiber is only 1/9 of the Nomex fiber.Accordingly,the excellent flame retardancy of polyimide fibers indicating them more attractive as the fireproof materials in the field of emergency protection.

Erratum to:Excellent long-term reactivity of inhomogeneous nanoscale Fe-based metallic glass in wastewater purification(vol 63,issue 3,pg 453-466,2020)

In the version of the article originally published in the volume 63,ssue 3,2020 of Sci China Mater(2020,63(3):453-46,https:/doi.org/10.1007/s40843-019-1205-5),the affiliations of the authors were incorrectly labeled.