Melt Crystallization of Poly(butylene 2,6-naphthalate)

Poly(butylene 2,6-naphthalate)(PBN)is a crystallizable linear polyester containing a rigid naphthalene unit and flexible methylene spacer in the chemical repeat unit.Polymeric materials made of PBN exhibit excellent anti-abrasion and low friction properties,superior chemical resista nee,and outstanding gas barrier characteristics.Many of the properties rely on the presence of crystals and the formatio n of a semicrystalline morphology.To develop specific crystal structures and morphologies during cooling the melt,precise information about the melt-crystallization process is required.This review article summarizes the current knowledge about the temperature-controlled crystal polymorphism of PBN.At rather low supercooling of the melt,with decreasi ng crystal I izatio n temperature,0'-and a-crystals grow directly from the melt and organize in largely different spherulitic superstructures.Formation of a-crystals at high supercooling may also proceed via intermediate formation of a transient monotropic liquid crystalline structure,then yielding a non-spherulitic semicrystalline morphology.Crystallization of PBN is rather fast since its suppression requires cooling the melt at a rate higher than 6000 K-s_1.For this reason,investigation of the two-step crystallization process at low temperatu res requires application of sophisticated experimental tools.These in elude temperatureresolved X-ray scattering techniques using fast detectors and synchrotron-based X-rays and fast scanning chip calorimetry.Fast scanning chip calorimetry allows freezi ng the transie nt liquid-crystalline structure before its con version into a-crystals,by fast cooling to below its glass transition temperature.Subsequent an alysis using polarized-light optical microscopy reveals its texture and X-ray scatteri ng con firms the smectic arrangement of the mesogens.The combination of a large variety of experimental techniques allows obtaining a complete picture about crystallization of PBN in the entire range of melt-supercoolings down to the glass transition,including quantitative data about the crystallization kinetics,semicrystalline morphologies at the micrometer length scale,as well as nanoscale X-ray structure information.     

Ce掺杂6H-SiC电子结构和光学性质的第一性原理研究

采用基于密度泛函理论的第一性原理计算方法,对未掺杂及Ce掺杂6H-SiC的电子结构和光学性质进行理论计算.计算结果表明,未掺杂6H-SiC是间接带隙半导体,其禁带宽度为2.045 eV,掺杂Ce元素,带隙宽度下降为0.812 eV.未掺杂6H-SiC在价带的低能区,Si-3s、C-2s电子轨道对态密度的贡献较大,在价带的高能区,主要是由Si-3p、Si-3s、C-2p态组成.掺杂后Ce原子的4f轨道主要贡献在导带部分,掺杂后电导率提高.未掺杂时,只有一个介电峰,是价带电子跃迁到导带电子所致,掺杂后有两个介电峰,第一个介电峰是由于导带电子跃迁到Ce原子4f轨道上产生,第二个峰是价带电子向导带电子跃迁产生.未掺杂6H-SiC,在能量为10.31 eV处吸收系数达到最大值,掺杂后在能量为6.57 eV处,吸收系数达到最大值.     

以磷化铁为添加剂沿(111)面生长磷掺杂金刚石大单晶

掺杂是调控金刚石性能的一种重要手段。本文采用温度梯度法,在5.6 GPa、1 312 ℃的条件下,选用Fe₃P作为磷源进行磷掺杂金刚石大单晶的合成。金刚石样品的显微光学照片表明,随着Fe₃P添加比例的增加,金刚石晶体的颜色逐渐变深,包裹体数量逐渐增加,晶形由板状转变为塔状直至骸晶。金刚石晶形的变化表明Fe₃P的添加使生长金刚石的V形区向右偏移,这是Fe₃P改变触媒特性的缘故。红外光谱分析表明,Fe₃P的添加使金刚石晶体中氮含量上升,这说明磷的进入诱使氮原子更容易进入金刚石晶格中。激光拉曼光谱测试表明,随着Fe₃P添加比例的增加,所合成的掺磷金刚石的拉曼峰位变化不大,其半峰全宽(FWHM)值变大,这说明磷的进入使得金刚石晶格畸变增加。XPS测试结果显示,随着Fe₃P添加比例的增加,金刚石晶体中磷相对碳的原子百分含量也会增加,这意味着添加Fe₃P所合成的金刚石晶体中有磷存在。     

A multifunctional separator with Mg(OH)2 nanoflake coatings for safe lithium-metal batteries

Dendrite growth and thermal runaway induce serious safety hazards,impeding the practical applications of lithium metal batteries(LMBs).Although extensive advances have been attained in terms of LMB safety,most work only focus on a single aspect at a time.This paper reports a multifunctional separator coated by Mg(OH)2 nanoflakes with various excellent properties including electrolyte wettability,ionic conductivity,Li+ transference number,puncture strength,thermal stability and flame retardance.When used in LMBs,the Mg(OH)2 nanoflake coatings enable uniform Li+ distributing,which makes it homogeneous to deposit lithium,realizing effective dendrite suppression and less volume expansion.Meanwhile,Mg(OH)2 coatings can ensure LMBs are in normal conditions without thermal runaway until 140 ℃.A part of lithium can be converted into Li+ ions by Mg(OH)2 during repeated charge/discharge cycles,not only reducing the risk of separator damage and consequent short circuit,but also replenishing the capacity loss of LMBs.The Mg(OH)2 nanoflakes can coat on all kinds of commercial separators to improve their performances,which offers a facile but effective strategy for fabricating multifunctional separators and a comprehensive insight into enhancing LMB safety.     

2,2-双(4-氯-2-氟苄基)丙二酸二乙酯的晶体结构和密度泛函理论研究

标题化合物是一个重要的精细化工中间体,可用于制备嘧啶类、吡唑类等产品。本文利用红外光谱(IR)、质谱(MS)、核磁共振氢谱(¹H NMR)、核磁共振碳谱(¹³C NMR)和X-射线单晶衍射对此化合物进行了表征,并在B3LYP/6-311G(d, p)模式下使用密度泛函理论(DFT)计算了此化合物的最稳定晶体结构以及最高占有分子轨道(HOMO)和最低占有分子轨道(LUMO)能量。结果表明,通过DFT优化的分子结构与X-射线单晶衍射确定的晶体结构基本一致,该化合物属于单斜方P2(1)/n空间群,晶胞参数为:a=1.563 9(10) nm, b=0.778 6(4) nm, c=1.838 2(10) nm,Z=4, ρ_c＝1.345 g·cm^-3,R=0.047 7,R_w=0.138 7。     

A multi-directional controllable multi-scroll conservative chaos generator:Modelling,analysis,and FPGA implementation

Combing with the generalized Hamiltonian system theory,by introducing a special form of sinusoidal function,a class of n-dimensional(n=1,2,3)controllable multi-scroll conservative chaos with complicated dynamics is constructed.The dynamics characteristics including bifurcation behavior and coexistence of the system are analyzed in detail,the latter reveals abundant coexisting flows.Furthermore,the proposed system passes the NIST tests and has been implemented physically by FPGA.Compared to the multi-scroll dissipative chaos,the experimental portraits of the proposed system show better ergodicity,which have potential application value in secure communication and image encryption.     

Lamb波频域逆散射全聚焦成像方法研究

Lamb波因其传播距离远、衰减小常被用于板状结构的无损检测中,在基于Lamb波损伤检测的诸多成像技术中,全聚焦方法(Total Focus Method,TFM)方法因其成像分辨率高、信噪比高而受青睐。然而Lamb波的频散效应导致时域延时量不能被准确计算,进而影响传统TFM方法对损伤定位及成像的精度;此外,既有的TFM方法仅以回波幅值作为成像指标,忽略了Lamb波与损伤的相互作用,故而不能通过损伤表面的物理参数增强成像质量。针对这两个问题,本文首先在时域TFM基础上发展了频域TFM,在计算中纳入频散关系以规避频散的影响;其次以包含明确的损伤特征参数--反射率为成像指标,结合频域TFM方法建立损伤逆散射模型,以实现对损伤的准确成像。仿真和实验结果表明:频域逆散射TFM成像方法能够实现对铝板结构中的损伤检测,在工程实践中具有应用价值。     

Synthesis of a Nine-atom Germanium Cluster K_(0.5)[K(18-crown-6)]_(1.5)Ge_9·1.5en with Unprecedented “up” and “down” Chain Arrangement of Unit [-(Ge_9-K-Ge_9)~(3-)-]

A new complex K0.5[K(18-crown-6)]1.5Ge9·1.5en(1) which contains unprecedented "up" and "down" chain arrangement of unit [-(Ge-9-K-Ge9)3-] has been prepared by the reaction of K4Ge9 with HgS in ethylenediamine(en) in the presence of 18-crown-6(1,4,7,10,13,16-hexaoxacyclooctadecane), and characterized by X-ray structure analysis. The color of the title crystals(black), which is darker than that of the reported three compounds with chains of germanium clusters, may result from the naked K+ and their interactions with the chain. And the structure differences between 1 and the reported three compounds with chains of germanium have also been discussed.     

4′-苯基-2,2′∶6′,2″-三联吡啶镍配合物的合成与晶体结构

运用水热法合成了1个新的配合物[Ni(Phtpy)2](CH3COO)2(化合物1),(Phtpy=4′-苯基-2,2′∶6′,2″-三联吡啶),并通过X-射线单晶衍射方法确定了该化合物的晶体结构.结构分析表明化合物1属于三斜晶系,P-1空间群,晶胞参数a=0.905 60(8)nm,b=1.103 07(9)nm,c=2.020 14(15)nm,α=94.383 0(10)°,β=100.983 0(10)°,γ=106.312 0(10)°,V=1.883 1(3)nm3,Z=2,R1=0.087 2,wR2=0.183 1.配合物中存在3种氢键和多种π-π相互作用,使其成为一个3D配合物.     

三维锌基金属有机框架材料的合成及其晶体结构与热性能

以1,1'-双(二苯基膦)二茂铁氯化钯为催化剂,2,5-二溴苯甲醛和4-吡啶苯硼酸经"一锅法"反应合成了新化合物2,5-二(吡啶-4-基)苯甲醛(L)。以L和反式-4,4'-二苯乙烯二甲酸(H2SDA)为配体,与Zn(NO3)2·6H2O经溶剂热反应合成了一个四重穿插的三维金属有机框架材料[Zn2L(SDA)2]·2DMA(1),其结构和热性能经IR,元素分析,X-射线粉末衍射和TGA表征。1属四方晶系,P4(1)2(1)2空间群,晶胞参数a=17.452 0(9),b=17.452 0(9),c=18.360 6(14),V=5 592.1(6)3,Z=8,Dc=1.303 mg·cm-3,F(000)=2 268,μ=1.557 mm-1,R1=0.040 6,ωR2=0.114 7。1的结构中轮浆型双核Zn2(CO2)4单元被四个SDA分子连接形成一个二维层状结构,进而通过配体L桥连形成一个三维的网状结构,其热稳定性高达320℃。