Photoconductivity along the Polymer/Polymer Interface

Physics of the Solid State - The effect of photoexcitation on the electrical conductivity of the interface between two polydiphenylenephthalide (PDP) polymer films is discovered. It is shown that...     

Electroluminescence of a Polymer Film with a Polymer/Polymer Interface

JETP Letters - The effect of a two-dimensional quantum-confined structure formed at a polymer/polymer interface on the radiative recombination of excitons (i.e., electroluminescence) is...     

Polymer Light-Emitting Diode Using Conductive Polymer as the Anode Layer

The analysis based on series equivalent circuit indicates that the resistance of electrode layers is the major factor limiting the current density of polymer light-emitting diodes （PLEDs） at higher voltages. The conductivity of 790 S/cm for the PEDOT：PSS film is achieved by secondary doping. At a thickness of 240 nm, the sheet resistance of the polymer layer is 51 Ω/sq, which is comparable to that of lTO films. The current density and luminance of the PLEDs with the polymer anode layer is higher than the ITO anode device, suggesting that it is feasible to replace ITO anode with a highly conductive polymer in PLEDs.     

Dynamics of Polaron at Polymer/Polymer Interface

The migration of a polaron at polymer/polymer interface is believed to be of fundamental importance for the transport and light-emitting properties of conjugated polymer-based light emitting diodes. Based on the one- dimensional tight-binding Su-Schrieffer-Heeger （SSH） model, we have investigated polaron dynamics in a one- dimensional polymer/polymer system by using a nonadiabatic evolution method. In particular, we focus on how a polaron migrates through the conjugated polymer/polymer interface in the presence of external electric field. The results show that the migration of polaron at the interface depends sensitively on the hopping integrals, the potential barrier induced by the energy mismatch, and the strength of applied electric field which increases the polaron kinetic energy.     

pH敏感功能聚合物的研究

以荧光染料曙红为pH指示剂、甲基丙烯酸为单体、双甲基丙烯酸一缩二乙二醇酯为交联剂、庚烷为致孔剂,利用高分子聚合技术合成了pH敏感功能聚合物。考察制备pH敏感功能聚合物的影响因素条件及其pH响应行为。曙红染料在聚合物介质中由于极性的减弱,其最大荧光发射波长较在水溶液中红移,表观解离常数增大,对pH的响应区间向酸性方向移动。在最佳实验条件下,pH敏感功能聚合物对pH的响应范围为0～3.0,并且具有较好的可逆性和重现性。     

Polymer adsorption

We consider the adsorption of linear polymer and copolymer chains at surfaces and interfaces. We first remind de Gennes' theory for homopolymers, made of a single monomer species. Then we turn to multi block and random copolymers. In the latter case, we consider both cases when the A and B monomer species are distributed along the chain in a noncorrelated and correlated way, respectively. For each case, we discuss single chain adsorption and the saturation of the surface. Various measurable quantities are evaluated.     

Polymer brushes near the crystallization density

In this paper, polymer brushes are studied via molecular-dynamics simulations at very high grafting densities, where the crossover between the brush regime and the polymer-crystal regime is taking place. This crossover is directly observed with the structure factor and pair-correlation function. With increasing grafting density, this crystallization is progressing from the core layer of the brush towards the surface layer. The same process is analyzed using the lateral fluctuations of the monomers as a signature of their diminishing mobility. Additionally, bond forces and the chain excess free energy indicate a transition from the brush regime to the overstretched regime, which is in agreement with predictions of a modified self-consistent field theory.     

液晶聚合物/柔性链聚合物共混体系相分离形态

利用元胞动力学方法在二维情况下对浓度、取向序参量的含时Ginzberg Landau方程进行数值求解 ,研究了液晶聚合物 /柔性链聚合物共混体系的相分离动力学 ,考察了浓度、取向有序过程的耦合对相分离形态的影响 .结果表明 ,此耦合作用对相分离的时间进程以及相分离图样的空间排布都有影响 .液晶聚合物的取向有序相当于增加了两组分间的不相容性而促进两相分离 ;两个序参量在热力学方面的耦合使液晶聚合物趋向于沿着界面方向取向 ,而动力学方面的耦合使液晶聚合物分子沿着其取向方向扩散 ,相分离图样的空间排布由这两种效应共同决定 .通过极化率张量的定义用数值方法模拟得到了相分离体系的小角光散射图样 ,结果表明 ,散射强度分布具有方位角依赖性 ,它是由浓度、取向序参量的空间变化共同决定的 .     

Polymer collapse in the presence of hydrodynamic interactions

We investigate numerically the dynamical behaviour of a polymer chain collapsing in a dilute solution. The rate of collapse is measured with and without the presence of hydrodynamic interactions. We find that hydrodynamic interactions both accelerate polymer collapse and alter the folding pathway.     

聚合物中长程关联能的动力学研究

本文计算采用扩展的SSH哈密顿模型, 加上长程关联哈密顿量,在自然边界条件下,用绝热动力学方法研究了有限长反式聚乙炔链中平均关联能随时间的演化,计算了长程电子关联对极化子动力学的影响并计算了极化子状态下的长程关联能。结果发现,加入一个电子或空穴,平均关联能的大小随着时间呈非周期性阻尼振荡,经过一定时间后,平均关联能趋近一个恒定值,此时得到比较稳定的极化子位形。当格点增加时,长程关联能趋于恒定的时间逐渐缩短。     

Interpenetrating Polymer Networks

Interpenetrating polymer networks (IPNs) are a new class of polymer blends in network form in which at least one component is polymerized and/or cross-linked in the immediate presence of the other. IPNs possess several interesting characteristics in comparison to normal polyblends, because the varied synthetic techniques yield IPNs of such diverse properties that their engineering potential spans a broad gamut of modern technology. Interpenetrating polymer networks have shown excellent chemical resistance, hardness, elongation, tensile strength properties and higher compatibility. Hence, it can be concluded that using the IPN concept, it is possible to design the most desirable material for a specific end use requirement.     

Movement of Polymer Segments by Exciplex Emission of Pyrene and N,N-Dimethylaniline at the Polymer–Silica Interface

Intermolecular interaction between pyrenyl units linked on the silica surface and N,N-dimethylaniline (DMA) units of polymer segments coated on the silica was investigated. Exciplex emission between these units was observed. The spectral shape and the intensity of the exciplex emission depended on the sample preparative conditions. Emission decay curves had no rise components, which showed that preformed ground-state complexes between pyrene and DMA existed and there were various microenvironmental sites around the preformed complexes just after sample preparation. Annealing of the samples made the exciplex emission wavelength shift and its intensity increase, which meant that polymer segments that contacted with the silica surface moved to make the stable conformations during annealing. It was revealed that DMA units of polymer segments are more stable when they face to the polymer–silica interface than when they become part of the polymer bulk. After the samples were kept at room temperature for 1 month, the spectra of all the samples became the same, which showed that the most stable conformations of the polymer segments were at the polymer–silica interface.     

Revisiting the Entangled Chains of Polymer in the Carbyne Model

The Monte Carlo carbyne model is modified to investigate the glass transition of the simplified polymer chains. The stochastic bombardment between monomers is monitored by Metropolis algorithm with the help of the consideration of hard potential while the mobility of monomers is governed by its mass, scattering rate, and temperature. Our model is capable to show that the glass transition temperature reduces with decreasing film thickness and the formation of critical voids in the thinner polymer contributing to the glass transition that is much easier than the bulk polymer.     

Molecular structure of polystyrene at Air/Polymer and Solid/Polymer interfaces

IR-visible sum-frequency generation (SFG) spectroscopy has been used in a total internal reflection geometry to study the molecular structure of polystyrene (PS) at PS/sapphire and PS/air interfaces, simultaneously. The symmetric vibrational modes of the phenyl rings dominate the SFG spectra at the PS/air interface as compared to the antisymmetric vibrational modes at the PS/sapphire interface. This indicates approximately parallel orientation of the phenyl rings at the PS/air interface while nearly perpendicular orientation at the PS/sapphire interface, with respect to the surface normal.     

Branching Features of a Polymer

Two parameters characterizing the branching features of polymers, branching density (BD), and branching completeness (BC), are proposed. Both have values of zero (0) for linear polymers. Branching density has the values of 1/2, 2/3, and (f – 2)/(f – 1) for the fully and densest branched polymers formed from tri-, tetra-, and f-functional monomers typed AB _{f –1}. Branching completeness will reach the value of one (1) for a completely branched polymer, where all possible branching monomeric units have reacted at least tri-functionally and all units are either terminal or dendritic. Branching density is close to the mole fraction of terminal units, and BC is close to the mole fraction of dendritic and terminal units in the branching polymers. The major advantage of these parameters is their independence of the degree of polymerization (dp). Branching density depends on the functionalities (f) of monomer units; BC does not. The higher the fraction of the dendritic unit monomerically bonded to a higher number of other units (the higher the terminal units fraction), the denser branched the polymer and the higher the BD. The BC and BD can be used in a simple way for describing multicharacter branching systems and for comparing the branching characters among them without any theoretical limitations. Physical quantities (namely, the number of dendritic and terminal units and the degree of polymerization) used for BD and BC evaluation can be determined directly from practical analyses, where NMR is most useful. The BC and BD, however, do not concisely describe branching characteristics for a polymer with cyclization or crosslinking in its structure.     

On the Convergence of Cluster Expansions for Polymer Gases

We compare the different convergence criteria available for cluster expansions of polymer gases subjected to hard-core exclusions, with emphasis on polymers defined as finite subsets of a countable set (e.g. contour expansions and more generally high- and low-temperature expansions). In order of increasing strength, these criteria are: (i) Dobrushin criterion, obtained by a simple inductive argument; (ii) Gruber-Kunz criterion obtained through the use of Kirkwood-Salzburg equations, and (iii) a criterion obtained by two of us via a direct combinatorial handling of the terms of the expansion. We show that for subset polymers our sharper criterion can be proven both by a suitable adaptation of Dobrushin inductive argument and by an alternative—in fact, more elementary—handling of the Kirkwood-Salzburg equations. In addition we show that for general abstract polymers this alternative treatment leads to the same convergence region as the inductive Dobrushin argument and, furthermore, to a systematic way to improve bounds on correlations.     

Thermodynamic Aspects of Polymer Mixtures

There have been a great many studies on polymer mixtures both from a scientific and an engineering viewpoint and they have been reviewed by many authors^1–3 and in many books.^4–6 However, it is only recently that polymer mixtures have been shown to be analyzable by thermodynamics. One of the many reasons for this situation is that polymer mixtures had previously been believed to be incompatible with each other due to the small entropy of mixing for long polymer chains and positive energy of mixing usually observed between polymers. However, due to rapid progress in experimental techniques used to study the state of polymer mixtures such as small angle neutron scattering (SANS),⁷ small angle X-ray scattering (SAXS),⁸ pulsed nuclear magnetic resonance (NMR),^9,10 Fourier transform infrared absorption (FT-IR),¹¹ thermal analysis.¹² excimer fluorescence,¹³ etc., quite a few polymer mixtures showing compatibility in molecular or segmental scale have been found. Moreover, some polymer mixtures have been shown to exhibit lower critical solution temperature (LCST)-or upper critical solution temperature (UCST)-type phase diagrams for liquid/liquid equilibrium and melting point depression for liquid/crystalline polymer mixtures. Therefore, it becomes quite natural to treat these problems thermodynamically as extensions of polymer solution theories or theories for metallically.^2,14,15     

Elastic Behavior of Polymer Chains

在三维非格子模型中研究了高分子链的弹性行为. 使用蒙特卡罗方法在构相空间中对高分子链抽样,每种链都得到了超过109个样本,然后使用类橡胶弹力的非高斯理论对这些样本进行数值分析并进行统计分析. 通过观测链柔性以及伸长量对高分子链的均方末端距、平均能量、平均赫尔姆霍兹自由能、弹力、能量对弹力的贡献和熵对弹力的贡献等性质的影响,发现刚性链比柔性链更加容易被拉伸. 而由于熵的作用,当拉伸长度大到一定程度时,刚性链的拉伸难度会大大增加.