Thermal stability of electrochemically prepared polythiophene and polypyrrole

The degradation behaviour of electrochemically prepared polythiophene and polypyrrole has been studied by thermal gravimetric analysis technique. Studies on both the polymers show that they are more stable than polyacetylene but still undergo degradation reactions which involve two steps, viz. loss of dopant and then degradation of polymer backbone. The general features of degradation mechanisms are discussed.     

Stability and mechanical properties of electrochemically prepared conducting polypyrrole films

The stability and mechanical properties of polypyrrolep-toluene sulphonate films prepared under various preparation conditions were studied and are reported here. Relatively high retention of conductivity and flexibility properties in air at room temperature were found for the films. More stable films were produced from propylene carbonate diluent than from acetonitrile and solvent mixtures. Acid treatment caused conductivity to increase and the mechanical properties to decrease slightly. However, both properties decreased dramatically after exposure of the films to sodium hydroxide solution. The effect of solutions containing different vanadium ions was also observed, the films being stable in V³⁺ and V⁴⁺ acid solutions, but unstable in V⁵⁺ solutions. The thermal stability of polypyrrole films grown at different temperatures and from different solvents was considerably high and fairly constant. Anisotropy in the mechanical properties was also observed for the two directions (along and across) within the same plane of the film. Incorporation of the plasticizer, di-iso-butyl phthalate (DIBP) into the films improved the mechanical properties. A high extendable acrylic-polypyrrole composite film was also prepared, capable of straining over 100%.     

Enhanced electrical conductivity of polypyrrole/polypyrrole coated short nylon fiber/natural rubber composites prepared by in situ polymerization in latex

In this paper we report the characterization and properties of conductive elastomeric composites of polypyrrole (PPy) and PPy coated short Nylon-6 fiber (F-PPy) based on natural rubber (NR) prepared by in situ polymerization method. PPy/NR blends were prepared by polymerizing pyrrole in NR latex using anhydrous ferric chloride as oxidizing agent, p-toluene sulphonic acid as dopant and vulcastab VL as stabilizer. PPy/F-PPy/NR composites were prepared as above in presence of short nylon fiber. The products were coagulated out, dried, compounded on a two roll mill and moulded. The cure pattern, DC electrical conductivity, morphology, mechanical properties, thermal degradation parameters and microwave characteristics of the resulting composites were studied. Incorporation of PPy to elastomer retards the cure reaction whereas addition of fiber accelerates the cure reaction. DC conductivity up to 6.25 × 10⁻² was attained for NR/PPy/F-PPy system. The composites containing F-PPy exhibited better mechanical properties compared to NR/PPy systems. The absolute value of the dielectric permittivity, AC conductivity and absorption coefficient of the conducting composites prepared were found to be much greater than the gum vulcanizate. PPy and F-PPy were found to decrease the dielectric heating coefficient and skin depth significantly.     

Influence of adsorbed layers on the electrical conductivity of dispersed systems

We present the results of an experimental investigation of the effects of adsorbed layers on the conductivity of a charge of finely divided nickel particles.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 61, No. 3, pp. 369–372, September, 1991.     

聚电解质自组装膜对聚吡咯原位沉积的影响

采用聚电解质自组装膜对其体材料进行表面化学改性，通过原位聚合在基体材料上沉积聚吡咯薄膜。采用UV－Vis和SEM对聚吡咯薄膜的结构进行了表征，结果表明基体材料经聚电解质自组装膜处理后，能改变聚吡咯薄膜的结构与性能。其中聚苯乙烯磺酸钠自组装膜不仅能明显增加聚吡咯薄膜厚度和改善薄膜均匀性及其与基体材料的附着力，而且能明显改变聚吡咯薄膜的微观结构，提高其导电性。     

聚吡咯及其复合材料的合成与导电性能研究

以水为反应介质,用硅烷偶联剂(MPS)对纳米级粒子二氧化硅(SiO2)进行预处理,用化学氧化聚合方法合成了聚吡咯/二氧化硅(PPy/MPS-SiO2)复合材料.对影响聚合反应的诸因素(温度、时间、搅拌速度等)进行了探讨,利用红外光谱、元素分析、电镜、四探针技术表征了这些材料的组成、结构和性能.     

电子封装材料表面化学制备高导电率聚吡咯薄膜的研究

研究了在环氧树脂塑料封装材料表面制备导电聚吡咯(PPy)薄膜的化学聚合方法,分析了影响聚吡咯薄膜微观形貌、附着力及电导率的因素.用四探针法测聚吡咯薄膜的电导率,并用扫描电子显微镜(SEM)、红外光谱(IR)、X射线光电子能谱(XPS)进行了表征.通过对电子封装材料的表面预处理与改性,制得了附着性好、均匀连续的聚吡咯薄膜,经掺杂电导率达到了45.10S/cm.     

Preparation and electrical conductivity of SiO2/polypyrrole nanocomposite

In the present study we have chemically polymerized silica/polypyrrole (SiO₂/PPy) nanocomposite in the presence of sodium dodecyl benzene sulfate (SDBS) as dopant and iron chloride (FeCl₃) as oxidant. The SiO₂/PPy nanocomposite presents an electrical conductivity of 32.41 S cm⁻¹ and percolation threshold of 20 wt%. The resulting SiO₂/PPy nanocomposites have been extensively characterized in terms of their molecular structure, particle size, morphology, stability, and electroactivity. These SiO₂/PPy particles have a rather polydisperse morphology. The effects of synthesis parameters such as oxidant, PPy, SDBS, reaction temperature and time, on the electrical conductivity of the nanocomposite have been detailedly optimized. And the conducting nanocomposite presented a good environmental stability.     

Thermal conductivity and nanoindentation hardness of as-prepared and oxidized porous silicon layers

Porous silicon (PS) offers promising possibilities to be applied as thermal insulating material in thermal effect microsystems for its thermal conductivity (TC) is up to two orders smaller than that of bulk silicon. In order to find a compromise between efficient thermal isolation and good mechanical stability of PS, thermal oxidation of PS is commonly used to tune the mechanical and thermal properties of PS. Both TC and the hardness of as-prepared and oxidized PS have been thoroughly investigated. TC and the hardness of as-prepared and oxidized PS were measured using micro-Raman scattering and nanoindentation, respectively. Experimental results revealed that TC and the hardness of as-prepared PS, exhibiting a strong dependence on the preparing conditions, decrease with increasing porosities. After oxidization at different temperatures, TC of oxidized PS decreases with increasing oxidation temperatures, whereas the hardness increases a lot. PS with a moderate porosity of 73.4% oxidized at 600 °C has a compromise between low TC [2.100 W/(m K)] and high hardness (∼1.160 GPa). So this process finalizes this kind of oxidized PS to be used as a suitable thermal insulation substrate in thermal effect microsystems.     

Features of the current-voltage characteristics and temperature dependences of electric conductivity in porous silicon layers

A method of separating porous silicon (por-Si) layer without deformation from a silicon substrate, which virtually excludes almost any risk of subsequent degradation of the isolated por-Si layer is proposed. The current-voltage characteristics of por-Si have been measured in a temperature interval of 300–255 K. Direct measurements of the conductivity of por-Si have been performed for the first time and it is established that the conductivity has an activation nature for the current passage parallel to the por-Si sample surface.     

气相生长炭纤维/聚苯乙烯复合材料导电气敏性能的研究

用溶液共混法制备了气相生长炭纤维/聚苯乙烯(VGCF/PS)导电气敏复合材料.VGCF可以在基体中均匀的分散,显著地改善复合材料的电性能.复合材料在多种有机蒸气中都有很好的气敏性.同时,气敏响应程度受复合材料中炭纤维的含量和蒸气温度的影响.     

Study on electrical conductivity of single polyaniline microtube

The PANI microtubes with diameter of 200 nm were synthesized by the template synthesis technique. The electrical conductivity of individual PANI microtube was measured directly in the template channel using scanning probe microscope (SPM). The average conductivity of the microtube is 5.81 S/cm, which is higher than that of bulk PANI (1.75 S/cm). The higher average conductivity is due to the enhancement of electrical conductivity caused by the confined environment and ordered structure of the template channels. Moreover, most of the conductivities of the microtubes are in the range of 10⁰ S/cm magnitude, which suggests that the SPM method possesses good reproducibility and feasibility for conductivity measurement of individual microtubes.     

Influence of the deposition parameters on the morphology and electrical conductivity of PANI/PSS self-assembled films

The influence of deposition parameters, namely polymer concentration and pH of the deposition solution, cleaning, and drying steps on the morphology and electrical characteristics of polyaniline and sulfonated polystyrene (PANI/PSS) nanostructured films deposited by the self-assembly technique is evaluated by UV–Vis spectroscopy, optical and atomic force microscopy, and electrical resistance measurements. It is found that stirring the cleaning solution during the cleaning step is crucial for obtaining homogenous films. Stirring of the cleaning solution also influences the amount of PANI adsorbed in the films. In this regard, the drying process seems to be less critical since PANI amount and film thickness are similar in films dried with N₂ flow or with an absorbent tissue. It is observed, however, that drying with N₂ flow results in rougher films. As an additional point, an assessment of the influence of the deposition method (manual versus mechanical) on the film characteristics was carried out. A significant difference on the amount of PANI and film thickness between films prepared by different human operators and by a homemade mechanical device was observed. The variability in film thickness and PANI adsorbed amount is smaller in films mechanically assembled.     

Structure and morphology of aluminium doped Zinc-oxide layers prepared by atomic layer deposition

The aim of this work is to study the effects of deposition temperature and aluminium incorporation on the crystalline properties, orientation and grain size of atomic layer deposited ZnO layers. X-ray diffraction analysis revealed a change in the dominant crystallite orientation with increasing substrate temperature. The most perfect crystal structure and largest grain size was found at 2 at.% aluminium content. Accumulation of compressive strain developed a monotonous increase with the growth temperature. Electric resistivity showed no anisotropy despite the change in the orientation, therefore the dominant conduction mechanism is not grain boundary related.     

Preparation of well-defined blackberry-like polypyrrole/fly ash composite microspheres and their electrical conductivity and magnetic properties

Composites consisting of conducting polypyrrole (PPy) and fly ash (FA) or amino-functionalized fly ash (A-FA) were prepared by the in situ chemical oxidative polymerization method, respectively. The surface functionalization of fly ash (FA) with amino groups was found to play an important role in the formation of the well-defined blackberry morphology. The scanning electron microscopy (SEM) analysis showed that the well-defined blackberry-like morphology of the polypyrrole/amino-functionalized fly ash (PPy/A-FA) composites with size range of 0.3–5 μm and the surface of the composites became smoother with more A-FA charged in the in situ chemical oxidative polymerization. X-ray diffraction (XRD) analysis of the PPy/A-FA composites showed the similar patterns as FA, which revealed that the crystal structure of FA was well-maintained after the surface functionalization and the in situ chemical oxidative polymerization. Thermogravimetric analysis (TGA) showed that the thermal stability of PPy/A-FA composites was enhanced and this could be attributed to the retardation effect of amine-functionalized fly ashes as barriers for the degradation of polypyrrole. The composites possess high electrical conductivity at room temperature, weak temperature dependence of the conductivity and good magnetic properties.     

黑铅硅石复合材料的电导率特性研究

介绍了一种以黑铅硅矿石为主要填料的新型复合材料的电导率正负温度系数特性。分析了黑铅硅石填充量和电导率的关系以及温度变化对复合材料电导率的影响。结果表明,随着黑铅硅石含量的增加,复合材料电导率逐渐增加,在黑铅硅石含量为55%(质量分数)时电导率出现极大值后开始下降。电导率随温度变化在低于140℃时呈现NTC效应,超过后呈现PTC效应。     

铈掺杂多孔硅的形貌和光致发光研究

采用电化学方法在多孔硅中掺杂了稀土铈(Ce)元素.利用原子力显微镜表征了多孔硅和Ce掺杂多孔硅的表面形貌,采用荧光分光计对样品的光致发光(PL)特性进行了研究.多孔硅样品在480nm波长激发下PL谱上观察到两个发光峰,分别位于572和650nm;通过光致发光激发谱测量,得到位于572、650nm的发光峰对应的最佳激发波长分别为380和477nm.Ce掺杂多孔硅样品在480nm波长激发下,PL谱上只显示出多孔硅原有的发光增强;而在380nm波长激发下的PL谱上不仅显示多孔硅原有的发光增强,而且还出现了新的发光峰位于517nm.认为这分别是Ce3 与nc-Si发生了能量传递和Ce掺杂引入了新的发光中心所造成的.     

Structural and electrical characteristics of epitaxial InP layers on porous substrates and the parameters of related Au-Ti Schottky barriers

The structures comprising three epitaxial InP layers—buffer (n ⁺⁺), active (n), and contact (n ⁺)—were grown by liquid phase epitaxy on porous and compact (control) InP(100) substrates. High quality of the active n-InP layer obtained on a porous substrate (in comparison to the control samples) is confirmed by the values of the halfwidths of the (311) X-ray diffraction reflections (54″ versus 76″), dislocation concentration (5×10²−5×10³ cm⁻² versus 5×10⁴−5×10⁵ cm⁻²), and electron mobility (4000 cm²/V s versus 3000–3500 cm²/V s). Using these homoepitaxial InP structures, Au-Ti Schottky diodes with a working mesastructure area of ∼1.8￠10⁻⁶ cm² were prepared. It was found that diodes based on the porous substrates are characterized by significantly smaller leak currents and higher breakdown voltages as compared to those of the control diodes: 1 nA, 27 V versus 200 nA, 15 V.