STUDIES ON ENHANCED CONDUCTIVITY OF STRETCHED CONDUCTING POLYMERS

A physical model of series of the conductivity on chain and the interchain conductivitybetween chains is proposed to explain enhanced conductivity of stretched conducting polymers.This model suggests that the enhanced conductivity for stretched conducting polymers might bedue to increasing of the interchain conductivity between chains along the elongation direction afterdrawing processes if the conductivity on chain is assumed much larger than that of the interchainconductivity between chains. According to this model, it is expected that the temperaturedependence of conductivity measured by four-probe method for stretched conducting polymers iscontrolled by a variation of the interchain conductivity between chains with temperature, whichcan be used to explain that a metallic temperature dependence of conductivity for stretchedconducting polymers is not observed although the conductivity along the elongation direction isenhanced by two or three orders of magnitude.     

Three-Strand Conducting Ladder Polymers: Two-Step Electropolymerization of Metallorotaxanes

Sequential polymerization of supramolecular metallorotaxane complexes results in three-stranded conducting ladder polymers. The internal polymer is "sandwiched" between the other two polymers to give molecular wires that are effectively insulated when the outer polymers are in their nonconducting state (shown schematically). The intermolecular conductivity can be mediated by the Cu(1+)/Cu(2+) redox couple.     

Thermal Properties of Polymers at Low Temperatures

Abstract

The existing measurements and theories of the low-temperature thermal properties, heat capacity, and thermal conductivity of polymers are reviewed with particular attention paid to the differences between partly crystalline and amorphous polymers. The most striking feature of the low-temperature heat capacity of polymers is that in the liquid helium temperature range the heat capacity does not depend upon the cube of the temperature as for other solids. Further, only well below 1°K does the heat capacity approach the value predicted on the basis of the sound velocity. This behavior indicates the presence of a small number of low-frequency modes of vibration in the frequency spectrum. The fact that such anomalous behavior seems linearly related to the crystallinity implies that this behavior is associated with the amorphous structure, perhaps with motions of pendent groups within cavities formed in the amorphous structure. The thermal conductivity of semicrystalline and amorphous polymers differs considerably. Semicrystalline polymers display a temperature dependence of the thermal conductivity similar to that obtained from highly imperfect crystals, the thermal conductivity having a maximum in the temperature range near 100°K which moves to lower temperatures and higher thermal conductivities as the crystallinity is increased. Amorphous polymers display a temperature dependence similar to that obtained for glasses with no maximum but a significant plateau region in the range between 5 and 15°K. The theoretical interpretation of the thermal conductivity of these materials is considered.     

共轭聚合物复合材料的结构和性能

对聚苯胺、聚吡啶等共轭聚合物与非导电聚合物材料的复合体系的结构和性能进行了综述。不同方法制备的复合材料在结构和性能上各有特点。一般共轭聚合物与非导电高分子材料相容性差、尤其是低极性高分了。     

Charge carrier transport in heterogeneous conducting polymer materials

The similarities of conductivity mechanisms of composites and nanocomposites and doped conjugated polymers that are also characteristic of specific heterogeneity are discussed. It is shown that the formulae developed to account for internal heterogeneity of conductive polymers can be applied also for polymer composites in spite of low overall content of the conductive phase. For fully organic nanocomposites (reticulate doped polymers) showing metal-like conductivity and a crossover temperature effective contribution of metallic phase is estimated. Examples of different properties of nanoparticles forming conducting networks as compared with the bulk crystals are discussed.     

高分子阳离子导体的极性基效应

<正> 高分子阳离子导体是一类只有阳离子充作电荷载流子的高分子固体电解质,因它在直流条件下呈现稳定的离子电导率而受世界各国学者重视。作为具有实用价值的高分子电解质,阳离子导体的关键问题是室温下离子电导率太低(一般比相应的双离子导体低1—2个数量级),难以应用。因而,国内外在这方面的研究重点集中在提高离子电导率上,近年来我们利用共混,共聚和交联等手段对提高离子电导率方面做了仔细工作,其中以极性丙烯酰胺共聚方法较好,经改进后共聚物的锂离子电导率达到2.1×10~(-6)s/cm(25℃),但对极性基改进电导率的实质未经探讨,本文将在上述工作基础上对极性丙烯酰胺共聚改进导电性的实质进行详细分析,得出有益的理论数据。     

DTA中升温速率及样品热导率对T_g测量值影响的模拟研究

就不同升温速率和实际样品的不同热导率对差热分析 (DTA)中高分子材料的玻璃化转变曲线的影响进行了MonteCarlo模拟研究 ,发现当所有样品刚完成玻璃化转变时 ,在Tg 曲线中该特征点要低于Tg 的转变中点。转变中点所对应的样品温度肯定要高于实际的玻璃化转变温度。如果以玻璃化转变曲线的转变中点所对应的样品温度作为该材料的玻璃化转变温度 ,那么 ,升温速率越快、样品的热导率越小 ,所测得的玻璃化转变温度就越大 ,反之亦然。DTA测得的玻璃化转变温度与升温速率间有很好的线性依赖关系 ,但与样品热导率间的关系是非线性的     

导电高分子的最近进展

因为导电高分子结合了金属与塑料的优点,他们一直受到很大的关注。但是他们的应用受到一些因素的影响,包括他们的电学性质,稳定性和可加工性。近来,导电高分子的性能得到很大的提高。他们在许多领域的重要应用被论证,比如透明电极,可拉伸电极,神经界面,热电转换和能量储存。这篇文章简单综述了导电高分子的电导提高和它们在热电转换,超级电容器和电池的应用。     

Strategies for molecular designing of novel low-band-gap electrically conducting polymers

Molecular designing of low-band-gap electrically conducting polymers continues to be a major challenge of the field of electrically conducting polymers. Such polymers are expected to show not only good intrinsic conductivity but also possibly a good transparency in the visible spectrum for their use as infrared sensors/detectors. Low-band-gap polymers can also be of great interest as new polymeric materials for nonlinear optics. Various routes presently followed to achieve this designing with special reference to the donor-acceptor polymers and important results obtained with this route are briefly reviewed.     

Unified study of the different physical properties of amorphous polymers

Uptil now it has not been possible to explain the different physical properties of amorphous polymers using a model based on a single conceptual scheme. In this paper, a phenomenological model is proposed which tries to explain the mechanical, optical and thermal properties (both thermal conductivity and expansivity) of amorphous polymers. The model has similarities with the composite model, proposed by the present authors, which has proved to be successful in interpreting the different physical properties of semicrystalline polymers. The present model considers the bulk form of the polymer as an aggregate of microscopic units possessing intrinsic physical properties. On drawing, the development of anisotropy in different physical properties is supposed to be due to the development of preferred orientation of these units. The development of the preferred orientation has been estimated directly from birefringence data. The agreement between the calculated and experimental values of the elastic modulus, thermal conductivity and thermal expansivity of PVC, PMMA and PS is found to be reasonable good.     

Facile Synthesis of Supramolecular Ionic Polymers That Combine Unique Rheological,Ionic Conductivity,and Self‐Healing Properties

A new family of supramolecular ionic polymers is synthesized by a simple method using (di‐/tri‐)carboxylic acids and (di‐/tri‐)alkyl amines. These polymers are formed by carboxylate and ammonium molecules that are weakly bonded together by a combination of ionic and hydrogen bonds, becoming solid at room temperature. The supramolecular ionic polymers show a sharp rheological transition from a viscoelastic gel to a viscous liquid between 30 and 80 °C. This sharp viscosity decrease is responsible for an unprecedented jump in ionic conductivity of four orders of magnitude in that temperature range. As a potential application, this chemistry can be used to develop polymeric materials with self‐healing properties, since it combines properties from supramolecular polymers and ionomers into the same material.     

Conducting metallopolymers based on azaferrocene

A series of 2,5-thiophene-substituted 1',2',3',4',5'-pentamethylazaferrocene complexes were synthesized and electropolymerized to produce polymers with fully pi-conjugated backbones. The length and hence oxidation potential of the conjugated linker (the thiophene fragments) between the metal centers were varied to understand the influence of the metal-metal interactions on the overall electroactivity of the resulting polymer. These complexes were electrochemically polymerized, and the resulting polymers were characterized by cyclic voltammetry, in situ conductivity, and spectroelectrochemistry measurements. The iron-centered oxidations significantly increased the conductivity of the polymer. The results reveal that shorter conjugated linkers cause the onset of conductivity to occur at lower potentials. This effect implies that a superexchange mechanism is likely operative in the charge migration of these polymers.     

Polarization of ionic liquid and polymer and its implications for polymerized ionic liquids: An overview towards a new theory and simulation

Ionic liquid (IL)-containing polymers garner attention for electrochemical applications. This article overviews recent experimental and theoretical studies of polymer electrolytes that would be likely to cultivate new theoretical and computational frameworks for IL-containing polymers. The first two sections outline the uniqueness of ILs that differentiates them from inorganic salts in polymers and explore deviation from the concept of the metaphor “room-temperature molten salt.” Such distinct properties include (1) large intrinsic dipole moment and electronic polarizability, (2) hydrogen bonding, (3) π-interactions, (4) a broad distribution of charges over the entire ion, and (5) the anisotropy of the ions. Moreover, the complexity of these properties substantially increases when the ions are polymerized. Indeed, their exceptional features would overcome the hurdle due to a trade-off between ionic conductivity and mechanical robustness in inorganic salt-doped polymers. Given these facts, the rest of the article focuses on emerging trends in the study of the dielectric response, phase separation, ion conductivity, and mechanical robustness of the polymer electrolytes, highlighting outstanding observations in experiments that may inspire existing theory and simulation. Our discussion also includes improving computational complexity for IL-containing polymers. To this end, recent machine learning studies that consider ILs and polymer liquids are presented.     

Thermal conductivity behaviour of polymers around glass transition and crystalline melting temperatures

The thermal conductivity of five semi-crystalline and four amorphous polymers was determined within a wide range of temperature, starting at room temperature and going up to temperatures above the polymer melting point (Tm) for semi-crystalline polymers or above the glass transition temperature (Tg) for amorphous polymers. Two transient techniques were employed in the experimental investigation: the hot wire technique for the group of amorphous polymers, and the laser flash technique for the semicrystalline polymers. As expected, the experimental results show that Tg exerts a measureable influence on the thermal conductivity of amorphous polymers. In the case of semi-crystalline polymers, a singular behaviour of the thermal conductivity is observed within the Tm range. In order to explain the anomalous behaviour, the influence of these transition temperatures on the thermal conductivity behaviour with temperature has been analysed in terms of a phonon conduction process and temperature variations of specific heat and modulus of elasticity of the analyzed polymers.     

偶氮共轭聚合物光电特性研究进展

芳香环或杂环通过NN双键连接形成的化合物如偶氮苯、偶氮吡咯等具有π共轭结构,此类分子有顺反两种构型,他们可以在光照条件下相互转换。分子构型转变会影响电子的共轭程度及其离域特性,因此含环结构的偶氮共轭分子具有光调制特性。反式偶氮苯分子为平面结构,顺式构型分子两个苯环有一定角度的扭转分子不在同一平面,实验和理论计算结果表明偶氮苯分子的键长、键角等受溶剂和取代基影响;光照可以实现偶氮苯分子的导电性改变,目前认为其导电性改变的原因主要是光致顺反异构而改变分子尺寸而引起。通过氮氮双键连接的杂环共轭分子能显著地降低分子的能隙,并使共轭化合物在更宽的波长范围内有强吸收,能提高太阳能光伏电池的转换效率,是理想的有机光伏材料。文章还对偶氮共轭聚合物的合成方法做了介绍,分析了含偶氮结构的共轭聚合物的光相应研究现状及其未来发展趋势。     

导电聚合物热电材料研究进展

导电聚合物在室温下具有较高的电导率(σ)、较低的热导率(κ)、柔韧性好、易于合成、原料来源丰富、对环境无污染等优势,是目前最具有热电应用潜力的有机热电材料之一。然而,目前针对导电聚合物作为有机热电材料的相关研究依然处于初级阶段,其在空气气氛中的化学稳定性问题、低的热电优值及尚未完全明确的热电机制一直困扰着研究人员。本文主要针对以上问题,在对前人的研究成果进行综述的基础上对目前有机热电材料所面临的关键问题进行阐述和总结。     

可溶性共轭聚席夫碱的合成、表征及电性能

本文以对苯二胺分别与乙二醛、丁二酮、３，４－己二酮和４，５－辛二酮缩聚合成了四种主链结构相同而侧基各异的新颖共轭性聚席夫碱．采用红外光谱和元素分析等方法对聚合物进行了表征．发现带有侧烷基的共轭性聚席夫碱能溶于一般有机溶剂；不同侧基的聚席夫碱溶解性是：两基聚席夫碱＞乙基聚席夫碱＞甲基聚度夫碱．测定了四种共轭聚席夫碱的本征导电率及其与温度的关系，结果表明，聚合物具有半导体性质．当聚合物以碘掺杂后，导电率可从１０－１１－１０－１２Ｓ／ｃｍ增加到１０－３－１０－４Ｓ／ｃｍ．探讨了共轭聚合物的侧基取代对掺杂后导电性的影响．     

Modifying thermal transport in electrically conducting polymers: effects of stretching and combining polymer chains

If their thermal conductivity can be lowered, polyacetylene (PA) and polyaniline (PANI) offer examples of electrically conducting polymers that can have potential use as thermoelectrics. Thermal transport in such polymers is primarily influenced by bonded interactions and chain orientations relative to the direction of heat transfer. We employ molecular dynamics simulations to investigate two mechanisms to control the phonon thermal transport in PANI and PA, namely, (1) mechanical strain and (2) polymer combinations. The molecular configurations of PA and PANI have a significant influence on their thermal transport characteristics. The axial thermal conductivity increases when a polymer is axially stretched but decreases under transverse tension. Since the strain dependence of the thermal conductivity is related to the phonon scattering among neighboring polymer chains, this behavior is examined through Herman's orientation factor that quantifies the degree of chain alignment in a given direction. The conductivity is enhanced as adjacent chains become more aligned along the direction of heat conduction but diminishes when they are orthogonally oriented to it. Physically combining these polymers reduces the thermal conductivity, which reaches a minimum value for a 2:3 PANI/PA chain ratio.     

Measurement experimental set-up for thermal characterization of low thickness polymers

The characterization of the thermal properties of polymers represents a fundamental step in improving materials for energy harvesting processes. Thermal conductivity, for example, is measured by measuring heat flux and temperature difference. This study seeks to design and fabricate an experimental set-up to measure the thermal conductivity of low-thickness polymers at room temperature. It is unique in that it is an affordable and lightweight instrument developed using electrical resistance as a heater and a limited number of components. Error analysis and reproducibility analysis were carried out for the thermal conductivity. The instrument was found to be reliable in making thermal conductivity measurements with an average of ±7%.     

Water‐mediated transport in ion‐containing polymers

Water‐mediated ion conduction enables high conductivity in hydrated polymer membranes commonly used in electrochemical devices. Understanding the coupling of the absorbed water with the polymer matrix and the dynamics of water inside the polymer network across the full range of length scales in the membrane is important for unraveling the structure–property relationships in these materials. By considering the water behavior in ion‐containing polymers, next‐generation fuel cell membranes are being designed that exceed the conductivity of the state‐of‐the‐art materials and have optimized conductivity and permeability that may be useful in other types of devices such as redox flow batteries. Water–polymer associations can be exploited to tune the transport and mechanical property tradeoffs in these polymers. Measurements of water motion provide important criteria for assessing the factors that control the performance of these types of materials. This review article discusses current understanding of water behavior in ion‐containing polymers and the relationship between water motion and ion and molecular transport. © 2011 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2011