四臂星型聚电解质刷在外加三价盐离子和电场下的塌缩

本文采用Langevin动力学模拟的方法,研究存在三价盐离子时,接枝在带相反电荷的极板上的部分带电的四个臂星型链呈现出的塌缩现象. 结果表明,在电场作用下,接枝星型链的平均带电分数和盐浓度在带电单体和三价盐离子的竞争性吸附中起关键作用. 对于接枝在带相反电荷的极板上的带电分数较高的星型链,刷子会塌缩到接枝极板上,并会产生极板表面电荷的过度补偿现象. 当带电分数较低时,如果星型链所带电荷数与三价盐离子电荷数相同,即使在很低的盐浓度下,极板对三价盐离子的吸引能力也高于对星型链中的带电单体的吸引. 结果表明,星型链在带电分数较低的情况下,三价盐离子的加入不会导致接枝电极表面电荷的过度补偿. 此外,本文还研究了三价盐离子对电场作用下星型刷的拉伸的影响.     

Theoretical investigation on the oligothienoacenes under the influence of external electric field

Theoretical investigation on a series of oligothienoacenes has been carried out at the B3LYP/6-31G* level by considering the influence of the external electric field. With the electric field increasing, the carbon-carbon single bonds become shorter and the carbon-carbon double bonds become longer, resulting in a better conjugation. Due to the different electron density, the charge mobility of the sulfur is more obvious than that of the carbon. The highest occupied molecular orbital (HOMO)-lowest unoccupied molecular orbital (LUMO) gap decreases with the EF intensity increasing. The applied EF also changes the spatial distribution of the molecular orbits: LUMO and several higher orbitals shift to the high potential side, whereas HOMO and several lower ones shift to the low potential side. All these features behave more pronounced with increasing conjugated chain length.     

Field-induced self-assembly: does size matter?

ABSTRACT

Simulated external electric fields are applied to polarisable species containing either a monodisperse of bidisperse distribution of polarisabilities. The magnitude of the external field and the polarisabilities are systematically varied. The application of an external field (of sufficient magnitude) is found to induce chain formation (as expected). The monodisperse systems are found to ‘self-assemble’ with larger induced dipole moments effectively clustering in chains as a result of significant dipole-induced dipole effects. The distribution of the chain lengths is characterised as a function of the applied field and the atom polarisability. For the bidisperse systems, the external field induces chain formation and a partial segregation, in which the more polarisable species preferentially form chains. The chain lengths are again determined as a function of field strength and the atom polarisabilities. Scaling behaviour is analysed.     

Quasi-pyroelectricity in the TGS crystal

It has been shown that a side electrode perpendicular to the measurement ones can significantly enhance the transverse electric current in TGS. Such a current, measured in a zero external electric field, resembles the classic longitudinal one. However, the amplitude of the transverse current oscillation, observed while cooling and heating the sample, rises much more slowly with the time of the transverse electric field preliminary application. Such exposure to the transverse field is required prior to the measurements for the transverse current to be observed, in a similar way to a longitudinal field that is applied in order to achieve a single domain state before longitudinal pyroelectric current measurements. A huge difference in the time of reaction to the electric fields preliminarily applied in order to achieve the maximum amplitude of the current oscillations in both cases is the evidence that the transverse current cannot be considered to be originated just for geometrical reasons.     

Effects of an electric field on the electronic and optical properties of zigzag boron nitride nanotubes

We have investigated the electro-optical properties of zigzag BNNTs, under an external electric field, using the tight binding approximation. It is found that an electric field modifies the band structure and splits the band degeneracy. Also the large electric strength leads to coupling the neighbor subbands which these effects reflect in the DOS and JDOS spectrum. It has been shown that, unlike CNTs, the band gap of BNNTs can be reduced linearly by applying a transverse external electric field. Also we show that the larger diameter tubes are more sensitive than small ones. The semiconducting metallic transition can be achieved through increasing the applied fields. The number and position of peaks in the JDOS spectrum are dependent on electric field strength. It is found that at a high electric field, the two lowest subbands are oscillatory with multiple nodes at the Fermi level.     

Formation dynamics of bipolaron in a metal/polymer/metal structure

Charge injection process from metal electrode to a nondegenerate polymer in a metal/ polymer/ metal structure has been investigated by using a nonadiabatic dynamic method. We demonstrate that the dynamical formation of a bipolaron sensitively depends on the strength of applied electric field, the work function of metal electrode, and the contact between the polymer and the electrode. For a given bias applied to one of the electrode (V₀) and coupling between the electrode and the polymer (t^′), such as V₀=0.79 eV and t^′=1 eV, the charge injection process depending on the electric field can be divided into the following three cases: (1) in the absence of the electric field, only one electron tunnels into the polymer to form a polaron near the middle of the polymer chain; (2) at low electric fields, two electrons transfer into the polymer chain to form a bipolaron; (3) at higher electric fields, bipolaron can not be formed in the polymer chain, electrons are transferred from the left electrode to right electrode through the polymer one by one accompanying with small irregular lattice deformations.     

基于密度泛函理论的外电场下盐交联聚乙烯分子的结构及其特性

交联聚乙烯是主要的高压电缆绝缘材料.为了研究外电场对盐交联分子结构的影响,本文对Zn原子使用def2-TZVP基组, C, H, O原子使用6-31G(d)基组,运用明尼苏达密度泛函(M06-2X)对交联聚乙烯分子进行优化得到了它的稳定结构.并研究了不同外电场(0—0.020 a.u., 1 a.u.=5.142×10~(11)V/m)作用下盐交联聚乙烯分子结构和能量变化,外电场对前线轨道的能级和成分的影响,原子之间的键级、断键和红光光谱的变化.研究结果表明:随着电场的增大,交联聚乙烯分子从空间网状结构逐渐变成线性结构,总能量降低,但势能增大,偶极矩和极化率升高,交联聚乙烯分子的稳定性随着电场的增大而降低;最高占据轨道能级持续增大,最低空轨道能级从0.011 a.u.电场开始持续降低,能隙持续降低,临界击穿场强为11.16 GV/m;沿电场方向聚乙烯链端表现出亲核反应活性,它的C—C键更容易断裂,形成甲基碳负离子,逆电场方向聚乙烯链端表现出亲电反应活性,它的C—H键更容易断裂形成H正离子;分子红外光谱高频区吸收峰明显红移,低频区吸收峰既有红移又有蓝移.     

Adaptive optical properties of ER fluid incorporating composite particles

Electrorheological (ER) fluid is one of the popular materials used in smart materials and structures. The material properties of ER fluid can be changed markedly while an external electric field is imposed on ER fluid domain. In this paper, the optical properties of ER suspensions consisting of composite particles dispersed in silicone oil are investigated. Both dc and ac electric fields are utilized to be imposed on ER fluid. The transmissivity of light through ER fluid under various electric fields is detected and analyzed. It is shown that the transmissivity of light increases with the increasing electric field strength and time. The change of transmissivity is caused by the formation of particle chains. The higher the particle concentration, the faster the change occurs. When an ac electric field is applied, the transmissivity can be affected by the frequency of electric field.     

载流子在金属/聚对苯乙炔/金属结构中注入及输运的动力学研究

采用紧束缚的Su-Schrieffer-Heeger模型,利用非绝热动力学方法研究了载流子在金属/聚对苯乙炔(poly(p-phenylene vinylene,简记为PPV))/金属三明治结构中注入与输运的动力学过程.发现由于强的电子-晶格相互作用,注入的电荷在PPV链中形成波包,波包的形成与施加在金属电极上的偏压、PPV链上的电场强度及金属电极与PPV之间的界面耦合强度密切相关.在无外电场的情况下,当偏压达到临界值时电荷能够从金属电极注入到PPV链中并形成波包.随着电场强度的增大,波包能 关键词： 金属/聚对苯乙炔/金属结构 载流子输运 波包     

介观尺寸原子链中的等离激元：紧束缚模型

本文运用紧束缚模型对介观尺寸原子链的等离激发进行了系统的研究, 通过量子响 应理论和相无规近似得到了等离激元的本征频率方程, 通过该方程计算了系统中等离子体的激发能量, 并分别对体系的本征振荡以及外电场作用在原子链上发生共振的情况进行了研究. 结果表明, 体系在外场作用下发生共振时, 偶极矩的峰值与等离子体的激发态相对应, 说明外场此时激发了等离激元; 体系处在共振情况下, 电荷振荡的幅度远远大于非共振的情况, 相对来说体系的电荷虚部的共振更为明显. 对于体系的本征等离振荡频率, 同等长度时等离子体的激发能量总是大于同级的单电子激发能量; 等离激元的能谱与原子链的长度和电子密度以及系统的库仑关联强度都有很大关系; 在原子链长度保持不变的情况下, 等离子体的激发能量随电子数目的变化以半满为中心呈对称关系. 关键词： 纳米结构 一维原子链 等离激元     

Spin-tunneling time in a hybrid semimagnetic/semiconductor heterostructure with a single paramagnetic layer

We investigate spin-dependent tunneling times in a hybrid semimagnetic/semiconductor heterostructure with a single paramagnetic layer under the influence of both electric and magnetic fields. We find that the tunneling times for electrons strongly depend on the incident energy, the magnitude of the external fields, and on their spin orientation. The results indicate that the tunneling time for spin-up electrons can be longer than that for spin-down ones by up to several orders of magnitude. This implies that tunneling for spin-up and spin-down electrons are separated in time within the same heterostructure.     

外电场下2,2’,5,5’-四氯联苯的分子结构与电子光谱

多氯联苯(PCBs)是难降解有机污染物, 2, 2’, 5, 5’-四氯联苯(PCB52)是PCBs的一种, 研究通过对PCB52分子加外电场的方法来降解该物质. 采用密度泛函B3LYP方法在6-311+g(d)基组水平上优化并计算了不同外电场(-0.04–0.04 a.u.)作用下PCB52的基态分子结构参数、分子总能量、电偶极矩和电荷分布. 然后利用含时密度泛函方法研究了PCB52分子在外电场下的前六个激发态的波长、激发能量和振子强度的影响. 结果表明: 随着外电场的增加, 1C–21Cl和14C–20Cl键的键长增大; PCB52的两个苯环在外加电场下, 二面角增大, 分子毒性减弱; PCB52分子能隙减小, 导致分子更容易受激发而跃迁到激发态发生还原脱氯反应. 外电场的增大, 激发态的激发能在迅速减小, 吸收波长也迅速红移, 振子强度不再为零. 表明电场作用下, 分子易于激发和解离. 关键词： 2,2’,5,5’-四氯联苯 电场 基态 激发特性     

等离子体在任意强度的直流电场中产生电流的过程

通过Fokker-Planck模拟,研究了等离子体在任意强度的直流电场中产生电流的过程以及电子分布函数的演变过程.研究发现,不同强度的电场中等离子体的行为存在着明显的差别.在弱电场中,电流与电场满足Spitzer公式,且电流产生的响应时间约等于撤销电场后电流衰减的弛豫时间;在中等强度的电场中,电子分布函数呈现为静止Maxwell分布和漂移Maxwell分布之和,而且在中等强度或者强直流电场中弛豫时间也将远远大于响应时间.根据电子分布函数的演变规律,推导了一组类似于流体力学方程的公式,这组方程像Spitzer公式一样简便地描述了等离子体中电流与电场的关系,并且对电场强度没有限制.数值模拟显示这组方程比Spitzer公式更适用于等离子体的混合粒子模拟中. 关键词： 等离子体电流 电子分布函数 Fokker-Planck模拟 Spitzer公式     

电场不均匀性对外场中负离子光剥离的影响

用蒙特卡罗方法研究了不均匀外场中氢负离子的光剥离.模拟结果显示出电场的不均匀抑制了光剥离截面和相应调制函数的振荡.光剥离截面的高能部分比阅值附近部分对电场的不均匀性更为敏感.结後果对纯电场和平行电场与磁场两种情形均适用.     

Electrochemical characteristics of the dimercaptan-poly(ethylene oxide) grafted polyaniline electrodes

The electrochemical and transport properties of the 2,5-dimercapto-1,3,4-thiadiazole (DMcT)/poly(ethylene oxide) (PEO) grafted polyaniline electrodes and the DMcT/polyaniline electrode interfaced with the poly(acrylonitrile) (PAN) based solid-polymer-electrolyte (SPE) containing lithium perchlorate and ethylene carbonate were studied. Compared with the electrochemical and transport properties of the DMcT/polyaniline electrode, the capacitance and voltammetric current density, obtained by cyclic voltammetry, were increased for the electrode with low grafted polyaniline (less than 3 mol. %), while decreased when the applied copolymers were highly grafted ones. The charge transfer resistance obtained from impedance measurements was much smaller in the DMcT/PEO grafted polyaniline electrode than that in the DMcT/polyaniline electrode, and more pronounced reduction of charge transfer resistance was observed for the electrode with low grafted polyaniline. The diffusion coefficient of lithium cation in the electrode was increased when the PEO grafted polyaniline was used as an electrode material, however, the increase of the diffusion coefficient was less significant at higher graft degrees. All these changes in electrochemical and transport characteristics by the employment of PEO chains upon polyaniline backbones were attributed to the enhancement of lithium ion solvation and enlarged free volume in the electrode.     

Study of fast switching processes due to electric and magnetic fields-an NMR approach

Solid state NMR techniques have been developed to investigate dynamic molecular effects (e.g., molecular reorientations) due to simultaneously applied external electric fields on electrically sensitive materials such as liquid crystals (LC), liquid crystalline polymers (LCP) and polymeric electrets. Such effects can be observed only on relatively thin systems (10-200 μm). That means that many scans are necessary to achieve a sufficiently high signal-to-noise-ratio in the spectra (500-1000 scans). If the material is also magnetically sensitive, the electric field can be used to orient molecules in a starting orientational state and by switching-off the voltage to access fast reorientation processes in the magnetic field B₀. Until now, the behaviour of orientable molecular systems under the influence of electric fields has been investigated by means of a more or less quasistatic approach (LCP: 100 V, electrets: 1 kV) in equilibrium states. The achievable time resolution depends on the desired signal-to-noise-ratio. For the case of proton NMR this means a time resolution of about 10 min. However, very often switching processes occur on a much shorter time scale. Using conventional techniques it is impossible to observe fast (ca. 100 μs) electrically or magnetically induced reorientation processes. In this work, we present a concept to overcome the problems outlined above and to extend the area of our current in situ NMR investigations on thin electrically-switched or poled polymeric layers. The basic idea is to include synchronized electric pulses during the NMR experiment using the preparation and/or mixing periods of a 1D or 2D pulse sequence for the application of an orienting field (electric or magnetic) and to use the reversibility of the molecular switching phenomenon to achieve a sufficient signal-to-noise-ratio. The techniques extend the range of possible investigations from about 100 μs to approximately T₁ for correlated spectra (and to longer times of applied fields for uncorrelated spectra). Results are shown for a nematic LC and a nematic polymer having a similar side chain.     

时间分辨与偏振红外光谱研究电场诱导下手性反铁电液晶的 …

手性反铁电液晶分子中的各个不同片段、不同基团在电场诱导下展现不同的取向与取向分布。在交变电场的作用下,分子中各个部分的翻转动力学行为也表现的不同。     

电极材料及偏压极性对氧化物介质击穿行为的影响及机制

忆阻器和能量存储电容器具有相同的三明治结构,然而两个器件需要的操作电压有明显差异,因此在同一个器件中,研究操作电压的影响因素并对操作电压进行调控,实现器件在不同领域的应用是十分必要的一个工作.本文利用反应磁控溅射技术在ITO导电玻璃、Pt/Si基底上生长了多晶ZrO_2和非晶TaO_x薄膜,选用不同金属材料Au, Ag和Al用作上电极构建了多种金属/氧化物介质/金属三明治结构的电容器,研究了器件在不同偏压极性下的击穿强度.结果发现:底电极是ITO的ZrO_2基电容器在负偏压下的击穿电场比Pt电极器件稍大.不管底电极是ITO还是Pt, Ag作为上电极时器件的击穿强度均存在明显的偏压极性依赖性,正偏压下的击穿电场减小了一个数量级;相反,在Al作为上电极的Al/TaO_x/Pt器件中,正向偏压比负向偏压下的击穿电场增加了近2倍.上述器件的不同击穿行为分别可以由氧化物电极和介质界面层间氧的迁移和重排、电化学活性金属电极的溶解迁移和还原以及化学活性金属电极与氧化物界面的氧化还原反应来解释.该实验结果对有不同操作电压要求的器件,如忆阻器和介质储能电容器等在器件设计和操作方面具有指导意义.     

Branching of colloidal chains in capillary-confined nematics

We report on the observation of colloidal chain assembly and branching inside capillaries filled with a nematic liquid crystal. Because of the homeotropic anchoring of liquid crystalline molecules on the capillary and colloidal droplet surfaces, the assembly of droplets along the capillary axis is expected, producing a transformation of the nematic director field from an escape-radial to quasiradial configuration. However, the subsequent over time branching of the straight colloidal chains is counterintuitive. By numerical simulations, we demonstrate that chain branching can occur by overcoming an energy barrier and can at least dwell as a metastable configuration. Moreover, manipulation of colloidal chains by electric fields and their gradients demonstrates various regimes of chain behavior in electric fields.     

共轭高聚物中极化子散射引起的激子迁移(英文)

基于Su-Schrieffer-Heeger(SSH)模型并考虑到Brazovskii-Kirova对称破缺项,研究了共轭聚合物中注入极化子和激子在外电场下的散射过程.研究发现在外场作用下极化子总是能通过激子,而激子的运动行为则密切依赖于电场的强度.如果电场大于临界电场3.0×10~5V/cm,那么激子与极化子散射后并不发生任何运动;然而当电场小于此临界值时,激子将在极化子运动的相反方向上有一个明显的位移.激子在弱电场下所发生的这种迁移运动,是由于同极化子发生了慢散射作用.