Vibrational Modes Analysis of Poly （Vinylidene Fluoride—Trifluoroethylene）

The ground State geometry and vibrational modes of poly (vinylidene fluoride-trifluoroethylene) [P(VDF-TrFE)] molecular chains have been investigated by ab initio molecular orbital calculation. The gauche bonds in P(VDF-TrFE) are introduced by TrFE monomers. The vibrational Modes are localized within all-trans segments. These results cause the infrared absorption weaker and diffused, and may be responsible for dielectric relaxation of the copolymers.     

Folding of lattice protein model chains with fixed ends

Using Monte Carlo simulations, we have studied the folding dynamics and thermodynamics of geometricall yconstrained lattice protein model chains. The constraints are realized by fixing one or both terminals of the chains. By comparing the results with that of the free-end chains, we find that the folding behaviours of the end-constralned chains are not completely similar to that of the free-end chains. Both kinds of constraints on the chain ends affect the folding dynamics of the chains: i.e., the folding rate, but not the thermodynamics. The thermodynamic behaviour of the one-end-fixed chains shows less difference from that of the free-end chains, while the thermodynamic behaviour of the two-end-fixed chains has obvious difference from that of the free-end chains. The origin of these differences comes from the differences of the ergodicitv of the chains in the conformational space.     

Geometric phases and quantum phase transitions in inhomogeneous XY spin-chains:Effect of the Dzyaloshinski-Moriya interaction

We study geometric phases of the ground states of inhomogeneous XY spin chains in transverse fields with Dzyaloshinski--Moriya (DM) interaction, and investigate the effect of the DM interaction on the quantum phase transition (QPT) of such spin chains. The results show that the DM interaction could influence the distribution of the regions of QPTs but could not produce new critical points for the spin-chain. This study extends the relation between geometric phases and QPTs.     

Decondensation behavior of DNA chains induced by multivalent cations at high salt concentrations:Molecular dynamics simulations and experiments

Using molecular dynamics simulations and atomic force microscopy(AFM), we study the decondensation process of DNA chains induced by multivalent cations at high salt concentrations in the presence of short cationic chains in solutions.The typical simulation conformations of DNA chains with varying salt concentrations for multivalent cations imply that the concentration of salt cations and the valence of multivalent cations have a strong influence on the process of DNA decondensation. The DNA chains are condensed in the absence of salt or at low salt concentrations, and the compacted conformations of DNA chains become loose when a number of cations and anions are added into the solution. It is explicitly demonstrated that cations can overcompensate the bare charge of the DNA chains and weaken the attraction interactions between the DNA chains and short cationic chains at high salt concentrations. The condensation-decondensation transitions of DNA are also experimentally observed in mixing spermidine with λ-phage DNA at different concentrations of Na Cl/Mg Cl2 solutions.     

Periodic oscillation of quantum diffusion in coupled one-dimensional systems

We analytically show that quantum diffusion in the coupled system composed of two identical chains exhibits a well-defined periodic oscillation in both transverse and longitudinal directions with a frequency determined by the interchain hopping strength, no matter whether the chains are periodic or non-periodic. We illustrate the result through numerical work on the coupled periodic chains and the quasiperiodic Aubry-Andre-Harper(AAH) chains with various modulations of onsite potentials supporting extended, critical, and localized states. We further numerically show that quantum diffusion in the coupled chains of different degrees of disorder W exhibits an exponential decay oscillation similar to the behavior of an underdamped harmonic oscillator, with a decay time inversely proportional to the square of W and a slight frequency change proportional to the square of W. Moreover, quantum diffusions in the coupled systems composed of two different chains are numerically studied, including periodic/disordered chains, periodic/AAH chains, and two different AAH chains, which exhibit the same behavior of underdamped periodic oscillation if the onsite potential difference between two chains is smaller than the interchain hoping strength.Existence of this universal periodic oscillation is a result of spectral splitting of the iso-spectra of two chains determined by interchain hopping, independent of system size, boundary condition, and intrachain onsite potentials. Because the oscillation frequency and spreading distance of wavepacket can be tuned separately by interchain hopping and intrachain potentials, the periodic oscillation of quantum diffusion in coupled chains is expected to find applications in control of quantum states and in designing nanoscale quantum devices.     

Translocation of closed polymers through a nanopore under an applied external field

The dynamic behaviours of the translocations of closed circular polymers and closed knotted polymers through a nanopore, under the driving of an applied field, are studied by three-dimensional Langevin dynamics simulations. The power-law scaling of the translocation time τ with the chain length N and the distribution of translocation time are investigated separately. For closed circular polymers, a crossover scaling of translocation time with chain length is found to be τ～ N α , with the exponent α varying from α = 0.71 for relatively short chains to α = 1.29 for longer chains under driving force F = 5. The scaling behaviour for longer chains is in good agreement with experimental results, in which the exponent α = 1.27 for the translocation of double-strand DNA. The distribution of translocation time D(τ) is close to a Gaussian function for duration time τ < τ p and follows a falling exponential function for duration time τ > τ p . For closed knotted polymers, the scaling exponent α is 1.27 for small field force (F = 5) and 1.38 for large field force (F = 10). The distribution of translocation time D(τ) remarkably features two peaks appearing in the case of large driving force. The interesting result of multiple peaks can conduce to the understanding of the influence of the number of strands of polymers in the pore at the same time on translocation dynamic process and scaling property.     

Self-consistent field theory of adsorption of flexible polyelectrolytes onto an oppositely charged sphere

The adsorption of flexible polyelectrolyte （PE） with the smeared charge distribution onto an oppositely charged sphere immersed in a PE solution is studied numerically with the continuum self-consistent field theory. The power law scaling relationships between the boundary layer thickness and the surface charge density and the charge fraction of PE chains revealed in the study are in good agreement with the existing analytical result. The curvature effect on the degree of charge compensation of the total amount of charges on the adsorbed PE chains over the surface charges is examined, and a clear understanding of it based on the dependences of the degree of charge compensation on the surface charge density and the charge fraction of PE chains is established.     

Electrostatic Interactions Between Glycosaminoglycan Molecules

The electrostatic interactions between nearest-neighbouring chondroitin sulfate glycosaminoglycan (CS-GAG)molecular chains are obtained on the bottle brush conformation of proteoglycan aggrecan based on an asymptoticsolution of the Poisson-Boltzmann equation the CS-GAGs satisfy under the physiologicM conditions of articularcar tilage. The present results show that the interactions are associated intimately with the minimum separation distance and mutual angle between the molecular chains themselves. Further analysis indicates that the elec-trostatic interactions are not only expressed to be purely exponentiM in separation distance and decrease with the increasing mutual angle but also dependent sensitively on the sline concentration in the electrolyte solution within the tissue, which is in agreement with the existed relevant conclusions.     

Synthesis,structure, and properties of Ba_9Co_3Se_(15) with one-dimensional spin chains

A new compound with one-dimensional spin chains, Ba9Co3Se(15), was synthesized under high pressure and high temperature conditions and systematically characterized via structural, transport and magnetic measurements. Ba9Co3Se(15) crystallizes in a hexagonal structure with the space group P-6c2(No. 188) and lattice constants of a = b = 9.6765 ? and c = 18.9562 ?. The structure consists of trimeric face-sharing octahedral CoSe6 chains, which are arranged in a triangular lattice in the ab-plane and separated by Ba atoms. The distance of the nearest neighbor of CoSe6 chains is very large, given by the lattice constant a = 9.6765 ?. The Weiss temperature Tθ associated with the intra-chain coupling strength is about -346 K. However, no long-range magnetic order but a spin glass transition at ~ 3 K has been observed. Our results indicate that the spin glass behavior in Ba9Co3Se(15) mainly arises from the magnetic frustration due to the geometrically frustrated triangular lattice.     

Stability of conductance oscillations in carbon atomic chains

The conductance stabilities of carbon atomic chains(CACs) with different lengths are investigated by performing theoretical calculations using the nonequilibrium Green's function method combined with density functional theory.Regular even–odd conductance oscillation is observed as a function of the wire length.This oscillation is influenced delicately by changes in the end carbon or sulfur atoms as well as variations in coupling strength between the chain and leads.The lowest unoccupied molecular orbital in odd-numbered chains is the main transmission channel,whereas the conductance remains relatively small for even-numbered chains and a significant drift in the highest occupied molecular orbital resonance toward higher energies is observed as the number of carbon atoms increases.The amplitude of the conductance oscillation is predicted to be relatively stable based on a thiol joint between the chain and leads.Results show that the current–voltage evolution of CACs can be affected by the chain length.The differential and second derivatives of the conductance are also provided.     

共聚物P(VDF-TrFE)在高压下的电学性质与相变

 研究了共聚物P（VDF-TrFE）（物质的量分数分别为80%、20%）在室温下、14 GPa内的电容、电阻与压力的关系。实验结果表明，它在14 GPa内存在两个相交：第一个相变发生在1.1 GPa左右；而第二个相变发生在5～6 GPa左右。     

共聚物P(VDF-TrFE)在高压下的电学性质与相变(英)

研究了共聚物P（VDF－TrFE）（物质的量分数分别为80％、20％）在室温下、14GPa内的电容、电阻与压力的关系。实验结果表明，它在14GPa内存在两个相交：第一个相变发生在1．1GPa左右；而第二个相变发生在5～6GPa左右。     

Crystalline morphologies of P(VDF-TrFE) (70/30) copolymer films above melting point

To further understand the crystallization behavior from melts of P(VDF-TrFE) (70/30) copolymer, the morphologies of P(VDF-TrFE) copolymer thin and ultra-thin films are studied by AFM. It is found that P(VDF-TrFE) (70/30) copolymer films exhibit morphologic transition from big grains to fiber-like rods above melting point. And this may be on account of the molecule chains plastic flow and self-organization, corresponding to polymer homoepitaxy.     

Intriguing triboelectrification behavior of identical P(VDF-TrFE) polymers

We report an intriguing triboelectrification behavior of thermally treated P(VDF-TrFE) polymers. Cooled (C-) and annealed (A-) P(VDF-TrFE) films were prepared by the rapid cooling of the melt solution and the subsequent annealing, respectively. The C–P(VDF-TrFE) had sparse grains and small elastic modulus and surface charge density, while, the A-P(VDF-TrFE) had dense grains and large elastic modulus and surface charge density. When the polymers contacted ITO electrodes, the triboelectric outputs of C-(PVDF-TrFE) were larger than those of A-P(VDF-TrFE). When the polymers contacted each other, the triboelectric outputs of different P(VDF-TrFE) films were significantly larger than those of similar P(VDF-TrFE) films. Based on detailed X-ray photoemission spectroscopy results, we suggested that roughness-induced frictional heat and elastic modulus differences may play an important role in minute material and/or ion transfer during the triboelectrification of identical P(VDF-TrFE) polymers.     

Carbon Nanotube/P(VDF-TrFE) Nano-Composite Characterization by Total Reflection X-Ray Fluorescence

In continuation of our research on carbon nanotube/P(VDF-TrFE) nano-composites [1], total x-ray fluorescence (TXRF) is engaged in a novel characterization of these materials regarding their compositions, purities, and structural analysis. Samples such as single-walled carbon nanotubes (SWCNT), multi-walled carbon nanotubes (MWCNT), P(VDF-TrFE) copolymer, SWCNT/P(VDF-TrFE), and MWCNT/P(VDF-TrFE) were analyzed by TXRF. The synthetic quartz used as a substrate was analyzed as reference material for the TXRF measurements. The ethanol and the dimethylformamide (DMF) used as solvents for carbon nanotubes and copolymers respectively were also analyzed by TXRF to determine whether they have an influence or not on the TXRF of the previous material. The preliminary results showed that single-walled and multi-walled carbon nanotubes prepared by the arc-discharge method contain catalytic particles such as Fe, Co, and Ni used to obtain SWCNT while there were no metal or impurities in MWCNT. The TXRF spectrum of CNT/P(VDFTrFE) showed the same results as we found previously with background due to the P(VDF-TrFE) copolymer scattered signal. __________ Published in Zhurnal Prikladnoi Spektroskopii, Vol. 72, No. 5, pp. 700–702, September–October, 2005.     

典型高分子材料的固体核磁共振研究

本论文通过固体核磁共振（NMR）谱及动力学参量的测量,并结合X-射线衍射技术和DSC测量等研究了两种典型高分子材料的相结构、链的运动以及相与相之间的关系.  乙烯-醋酸乙烯共聚物( EVA) 是最主要的乙烯共聚物之一. 研究发现,EVA的相组成非常复杂,共有5个不同的组分. 除了PE中所观察到的常规单斜晶相和刚性的正交晶相外,我们发现还存在第三个晶相分量－运动性较强的晶相（SOCP,可能是转动相）. 它不仅拥有自己的熔点,而且它的化学位移和分子运动性不同于刚性正交晶相（LOCP）. 另一方面,非晶相也由两种不同的分量组成：运动受限的各相异性的非晶界面相和高度可动的橡胶型的非晶相. 我们进一步详细研究了EVA中的晶区链动力学和非晶区的低温冻结行为. 实验发现,在正交晶相中,高分子链以180° flip-flop方式运动,同时伴随沿链方向的平移型跳跃运动,并引起正交晶相和非晶相之间的长程链扩散,通过NOE的测量证实了这种相间链扩散的存在,并进一步通过实验证实这种相间链扩散是一种受限扩散而不是自由扩散. 同时非晶相的两个组分具有不同的低温冻结行为：当温度低于-弛豫转变温度时,橡胶型的非晶相中的长程分子运动被冻结,但仍存在分子的局域运动;而界面非晶在低温时冻结成一种有序取向结构,并用质子自旋扩散实验证实该有序结构与正交晶相相邻近.  少量纳米级片层状粘土分散在聚合物中就可赋予材料许多优异的性能,我们用固体NMR技术对EVA/REC复合材料的结构和其中粘土的分散性质进行研究,发现上述复合材料中所形成的晶体类型不仅依赖于各组分的性质还依赖于所形成的复合材料的类型.  偏氟乙烯/三氟乙烯共聚物（P（VDF-TrFE））是最主要的铁电高聚物之一. 我们利用变温固体¹⁹F MAS NMR 谱及弛豫数据的测量详细研究了电子辐照对P(VDF-TrFE)共聚物的分子结构、构型、运动性以及相变等的影响. 发现,电子辐照不仅改变了分子链段的构型和运动性,同时也改变了局部分子化学结构. 电子辐照促使铁电相向顺电相(或者非晶相)转变,与此同时诱发了富含VDF和含-TrFE链段从全反式的构型到混合的反式-旁式构型的转变. 电子辐照加剧顺电区域中的分子运动而在高温熔融态中(>100 ℃）,分子的运动反而受限.     

面外应变对1-3型垂直异质P(VDF-TrFE)基复合薄膜电热性能的调控

考虑1-3型垂直异质铁电P（VDF-TrFE）基复合薄膜结构,利用非线性的热力学理论分析和讨论了平面外应变对复合薄膜电热性能的调控作用. 结果表明,在施加的垂直电场下,平面外应变可以有效地调控电极化、热释电系数、绝热温差等铁电、电热性能. 通过合理的调控平面外应变可以在很大的温度区域范围内获得比纯平面外延薄膜结构更高的绝热温差. 研究结果预示着垂直异质P（VDF-TrFE）基复合薄膜结构在一定的工作温度范围内具有优异的电热性能,在微电源、光通信二极管、红外传感器等微型元件方面有着广泛的应用前景. 关键词： 电热效应 平面外应变 P(VDF-TrFE)复合薄膜 绝热温差     

Thermal motion of one-dimensional domain walls in monolayers of a polar polymer observed by Video-STM

Scanning tunneling microscopy (STM) has been used to investigate monolayers of the ferroelectric copolymer polyvinylidenefluoride/trifluoroethylene P(VDF/TrFE) showing images of ordered polymer monolayers. By scanning with video frame rate, direct observation of the motion of onedimensional domain walls was also possible for the first time. The images clearly show domain walls normal to the polymer chains. From measurements of the temperature dependence of the domain wall velocities the activation energy for the thermally generated kink motion was estimated. These results are compared with theoretical models describing domain wall motion in ferroelectric PVDF.     

Low-voltage pulse exciting electron emission from ferroelectric copolymer film cathode: Role of film thickness and emission stability

Ferroelectric copolymer thin films P(VDF-TrFE) are used as a ferroelectric cathode for investigation of their electron emission properties. This ferroelectric copolymer films with different thicknesses are deposited by spin-coating method, and then the annealing process is carried out to improve the crystallinities of as-deposited copolymer films. The measurement results of ferroelectric electron emission showed that the copolymer P(VDF-TrFE) films had a desired ferroelectric electron emission ability excited at low-voltage pulse, and its peak emission current can reach to be ∼1.3 μA when the pulse voltage is 280 V. In addition, the effect of film thickness on electron emission property and emission stability of copolymer thin film P(VDF-TrFE) are discussed.     

Fabrication of broadband poly(vinylidene difluoride-trifluroethylene) line-focus ultrasonic transducers for surface acoustic wave measurements of anisotropy of a (1 0 0) silicon wafer

This paper investigates a new method for fabrication of broadband line-focus ultrasonic transducers by sol–gel spin-coating the poly(vinylidene difluoride-trifluroethylene) [P(VDF-TrFE)] copolymer film on a concave fine-polished beryllium copper backing. The ferroelectric hysteresis loops of the P(VDF-TrFE) films spin-coated from different molar ratios of VDF/TrFE, 77/23 and 55/45, were measured to select the better mixture. Owing to the better acoustic matching to water, compared with lead zirconate titanate (PZT), the fabricated transducers show relatively wide bandwidth of approximately 50 MHz with high central frequency of 60 MHz obtained at the focal plane when a fused-quartz acts as a reflecting target. Each one of the two finished transducers has a focal length of 5 mm and a full aperture angle of 90°. After applying the specially developed digital signal processing algorithm to the defocusing experiment data, which is called V(f,z) analysis method based on two-dimensional fast Fourier transform (2-D FFT), the operating frequency can extend from several MHz to over 90 MHz. Surface acoustic wave (SAW) velocities of a typical (1 0 0) silicon wafer was measured along various directions between [1 0 0] and [0 1 0] to represent the anisotropic features.