Decay of electrical conductivity in p-toluene sulfonate doped polypyrrole films

Long term performance of conductivity of p-toluene sulfonic acid (pTSA) doped electrochemically synthesized polypyrrole (PPy) films was estimated from accelerated aging studies between 80 °C and 120 °C. Conductivity decay experiments indicated that overall aging behavior of PPy films deviated from first order kinetics at prolonged aging times at elevated temperatures. However, an approximate value for the activation energy of the conductivity decay of PPy was calculated as E=47.4 kJ/mol, enabling an estimate of a rate constant of k=8.35×10⁻⁶/min at 20 °C. The rate of decrease of conductivity was not only temperature dependent but also influenced by the dopant concentration. A concentration of 0.005 M pTSA in the electrolyte resulted in a conductive film and when this film was exposed to 120 °C for a period of 40 h, the conductivity decayed to about 1/20 of its original value. The concentration of pTSA was increased to 0.05 mol/l and when the resulting film was aged in the same way, it showed a decrease in the conductivity to about 1/3 of its original value. Both microwave transmission and dc conductivity data revealed that highly doped films were considerably more electrically stable than lightly doped films. The dopant had a preserving effect on the electrical properties of PPy.     

Electrospinning and microwave absorption of polyaniline/polyacrylonitrile/multiwalled carbon nanotubes nanocomposite fibers

Electrical conductive nanocomposite fibers were prepared with polyaniline (PANI), polyacrylonitrile (PAN) and multi-walled carbon nanotubes (MWCNTs) via electrospinning. The morphology and electrical conductivity of the PANI/PAN/MWCNTs nanocomposite fibers were characterized by scanning electron microscope (SEM) and Van De Pauw method. Electrical conductivity of nanocomposite fibers increased from 1.79 S·m^?1 to 7.97 S·m^?1 with increasing the MWCNTs content from 3.0 wt% to 7.0 wt%. Compared with PANI/PAN membranes, the mechanical property of PANI/PAN/MWCNTs nanocomposites fiber membranes decreased. The microwave absorption performance of composite films was analyzed using waveguide tube, which indicated that with the thickness increasing the value of R_L reduced from ?4.6 to ?5.9 dB.     

Morphology and properties of polyacrylonitrile/single wall carbon nanotube composite films

Composite films were prepared by casting the solution of polyacrylonitrile (PAN) and single wall nanotube (SWNT) in DMF subsequent to sonication. The SWNTs in the films are well dispersed as ropes with 20–30 nm thickness. Moreover, AFM surface image of the composite film displays an interwoven fibrous structure of nanotubes which may give rise to conductive passways and lead to high conductivity. The polarized Raman spectroscopy is an ideal characterization technique for identification and the orientation study of SWNT. The well-defined G-peak intensity at 1580 cm⁻¹ shows a dependency on the draw ratio under cross-Nicol. The degree of nanotube orientation in the drawn film was measurable from the sine curve obtained by rotating the drawn film on the plane of cross-Nicol of polarized Raman microscope. The threshold loading of SWNT for electrical conductivity in PAN is found to be lower than 1 wt% in the composite film. The electrical conductivity of the SWNT/PAN composite film decreased with increasing of draw ratio due to the collapse of the interwoven fibrous network of the nanotubes with uniaxial orientation.     

Structural investigation of anionic functional poly(vinyl alcohol) doped polypyrrole nanospheres

This article reports on a facile route for the preparation of polypyrrole nanospheres with improved water solubility, ordering and conductivity in the presence of a polyelectrolyte, such as phosphorylated polyvinyl alcohol. The phosphorylated polyvinyl alcohol (PPVA) was used as both the stabilizer and the dopant in the chemical oxidative polymerization of pyrrole. The resulting PPVA doped polypyrrole (PPy) nanocomposites (PPy-PPVA) were characterized with FTIR, TGA, SEM and AFM techniques. The electrical conductivity of polymer was measured by four-point probe method. Our observation and results suggest a plausible formation mechanism of PPy nanospheres, PPVA micelle might have functioned as ‘template’ during the polymerization of pyrrole monomers, meanwhile, the PPy chains doped with phosphate group. It was found that the size decreased and their dispersion stability in water increased with the increasing feeding ratio of PPVA. The conductivity of PPy with different morphologies was also measured and compared. When the PPVA: pyrrole feeding ratio ranged from 20 to 50 wt%, the PPy-PPVA nanoparticles showed spherical shape with excellent uniformity, good electrical conductivity (up to 33.1 S·cm^?1), and weakly temperature dependent conductivity. It’s worth mentioning that the PPy-PPVA nanocomposite prepared in high PPVA feeding ratio has been well-dispersed for more than 24 months, which indicates its significant dispersion stability.     

Synthesis and characterization of electrically conductive composite films of polypyrrole/poly(acrylonitrile-co-styrene)

Homogeneus Polypyrrole (PPy)/poly(acrylonitrile-co-styrene) (SAN) composite thin films were prepared by chemical polymerization of pyrrole on poly(acrylonitrile-co-styrene) matrix. Ce (IV) is used as an oxidant for in-situ polymerizion of pyrrole on SAN matrix, having an advantageous over the impregnation method. The formation and incorporation of PPy in the copolymer matrix were confirmed by FTIR-ATR and UV-Visible spectrophotometric measurements. Thermal analyses showed that after polymerization of Py in copolymer matrix, thermal behavior of SAN was changed and derivative of weight loss at this temperature was increased by increasing of PPy content. XPS and FTIR-ATR analysis of composite films indicated cerium salt with nitrate ion acted as a dopant. The increase in the AC electrical conductivity of the PPy/SAN composites over pure SAN was observed. At lower frequency up to 10⁵ Hz, conductivity was shown an independent behavior from frequency; but at high frequencies (10⁵–10⁷ Hz), dependence on frequency was explained by polaron and bipolaron formations of PPy. The dispersion of PPy particles in copolymer matrix was proven by SEM, AFM and digital camera. By the increase of PPy content in the composite films, increase in AC conductivities, and decrease in dielectric constants and loss were observed.     

Effects of microwave irradiation on the basic properties of woodceramics made from carbonized tobacco stems impregnated with phenolic resin

A series of woodceramics derived from carbonized tobacco stems and phenolic resin composite heated by microwave irradiation was prepared and effects of microwave irradiation time, power and mass fraction of phenolic resin in woodceramics on the mass loss ratio, volume shrinkage ratio, apparent density, open porosity and volume electrical resistivity were investigated systematically. The pyrolysis behaviours of tobacco stems, phenolic resin and carbonized tobacco stems/phenolic resin composite were also evaluated using thermogravimetry. The experimental results showed that the mass loss ratio, volume shrinkage ratio and apparent density increased, while the volume electrical resistivity and open porosity decreased with increasing microwave irradiation time. The apparent density increased, while the mass loss ratio, volume shrinkage ratio, volume electrical resistivity and open porosity decreased with an increase in the mass fraction of phenolic resin. The mass loss ratio, volume shrinkage ratio and open porosity increased, while apparent density and volume electrical resistivity decreased with an increase in the microwave power. Microstructures of woodceramics obtained at various microwave irradiation time were characterized by scanning electron microscopy (SEM) technique, which confirmed the results of pyrolysis analyses of samples and effects of microwave irradiation on basic properties of woodceramics prepared.     

Comparative evaluation of seed coat dormancy breaking treatments in Stylosanthes seabrana

The efficiency of microwave treatment in breaking the hard seed coat dormancy in Stylosanthes seabrana was compared with three other conventional methods including mechanical scarification, hot water treatment (100°C for 1 min) and acid scarification (5 min). The microwave treatment was as efficient in breaking hard seed coat dormancy as the hot water treatment. The ranking of treatments followed the order microwave ≥ hot water ≥ acid > mechanical scarification > control. The electrical conductivity of microwave‐treated seeds, although less than that of hot water, was greater than untreated control seeds, indicating increased permeability of the seed coat for water uptake. Seedling vigour, based on seedling length, was also similar for these treatments. Respiration was found to be higher in microwave‐treated seeds. Although levels of food reserves were not measured, future studies could hypothesize that increased imbibition of water in microwave‐treated seeds could cause a faster breakdown of food‐reserve material that is supplied to the germinating seed, resulting in increased evolution of CO₂ through respiration. Scanning electron micrographs indicated the appearance of cracks and blisters on the seed surface of microwave‐treated seeds. These are most likely the sites of water entry during imbibition.     

高温胁迫下茄子耐热性表现及耐热指标的筛选

对7份茄子材料分别进行室内高温鉴定和田间自然高温鉴定,并探讨2种鉴定方式的相关性,以筛选适宜、快速、准确的鉴定指标。结果表明：除可溶性糖外,幼苗热害指数、细胞膜相对电导率、脯氨酸含量、丙二醛（MDA）可有效的评价不同茄子幼苗的耐热性。田间高温条件下,经室内鉴定为耐热品种的正常花率和坐果率均高于不耐热品种。经相关分析结果可知,各品种的正常花率和坐果率与苗期热害指数、细胞膜相对电导率、脯氨酸含量、MDA含量呈显著性相关。本研究结果表明细胞膜相对电导率、脯氨酸含量、MDA及热害指数可作为茄子耐热性快速鉴定的指标。     

Properties and performance of polypyrrole (PPy)-coated silk fibers

Different silk substrates in form of spun silk tops, nonwoven web, yarn, and fabric were coated with electrically conducting doped polypyrrole (PPy) by in situ oxidative polymerization from an aqueous solution of pyrrole (Py) at room temperature using FeCl₃ as catalyst. PPy-coated silk materials were characterized by optical (OM) and scanning electron (SEM) microscopy, FT-IR spectroscopy, and thermal analysis (DSC, TG). OM and SEM showed that PPy completely coated the surface of individual silk fibers and that the polymerization process occurred only at the fiber surface and not in the bulk. Dendrite-like aggregates of PPy adhered to the fiber surface, with the exception of the sample first polymerized in the form of tops and then spun into yarn using conventional industrial machines. FT-IR (ATR mode) showed a mixed spectral pattern with bands typical of silk and PPy overlapping over the entire wavenumbers range. DSC and TG showed that PPy-coated silk fibers attained a significantly higher thermal stability owing to the protective effect of the PPy layer against thermal degradation. The mechanical properties of silk fibers remained unchanged upon polymerization of Py. The different PPy-coated silk materials displayed excellent electrical properties. After exposition to atmospheric oxygen for two years a residual conductivity of 10–20 % was recorded. The conductivity decreased sharply under the conditions of domestic washing with water, while it remained essentially unchanged upon dry cleaning. Abrasion tests caused a limited increase of resistance. PPy-coated silk tops were successfully spun into yarn either pure or in blend with untreated silk fibers. The resulting yarns maintained good electrical properties.     

Fabrication of Biocompatible PLGA/PCL/PANI Nanofibrous Scaffolds with Electrical Excitability

Application of electrospun nanofibrous scaffolds has received immense attention in tissue engineering. Fabrication of scaffolds with appropriate electrical properties plays a key role in neural tissue engineering. Since fibers orientation in the scaffolds affects the growth and proliferation of the cells, this study aimed to prepare aligned electrospun conductive nanofibers by mixing 1 %, 10 % and 18 % (w/v) doped polyaniline (PANI) with polycaprolactone (PCL)/poly lactic-coglycolic acid (PLGA) (25/75) solution through the electrospinning process. The fibers diameter, hydrophilicity and conductivity were measured. In addition, the shape and proliferation of the nerve cells seeded on fibers were evaluated by MTT cytotoxicity assay and scanning electron microscopy. The results revealed that the conductive nanofibrous scaffolds were appropriate substrates for the attachment and proliferation of nerve cells. The electrical stimulation enhanced neurite outgrowth compared to those PLGA/PCL/PANI scaffolds that were not subjected to electrical stimulation. As polyaniline ratio increases, electric stimulation through nanofibrous PLGA/PCL/PANI scaffolds results in cell proliferation enhancement. However, a raise more than 10 % in polyaniline will result in cell toxicity. It was concluded that conductive scaffolds with appropriate ratio of PANI along with electrical stimulation have potential applications in treatment of spinal cord injuries.     

Rice genotype and fertilizer management for improving rice productivity under saline soil conditions

Paddy and Water Environment - Soil salinity is a threat to crop production in the Senegal River Delta where salt intrusion increases soil electrical conductivity and most of farmers had abandoned...     

Surface characterization of aromatic thermotropic liquid crystalline fiber deposited by nanostructured silver

Nanostructured silver thin films were sputtered onto the aromatic thermotropic liquid crystalline fibers of Vectran by magnetron sputtering technology. Plasma treatment was used as pre-treatment in order to improve the deposition of the coating layer. Surface morphology of the coated fibers was examined by scanning electron microscopy (SEM) and atomic force microscopy (AFM). A full energy dispersive X-ray analysis (EDX) was used to detect the elemental composition of the material. Its conductivity and mechanical properties were measured and analyzed as well. The study revealed that a very thin conductive silver deposition exhibited high electrical conductivity as well as less influence on the mechanical properties of the pre-treated Vectran fiber. The plasma treatment could improved the deposition of the coating layer, but the surface roughness caused by plasma treatment also affected the surface conductivity. It was found that the surface resistivity could reach very low value of 1.66×10⁻³ Ω·cm after sputtering deposition for 30 min.     

Influence of the draw ratio on the mechanical properties and electrical conductivity of nanofilled thermoplastic polyurethane fibers

Electrically conducting textile fibers were produced by wet-spinning under various volume fractions using thermoplastic polyurethane (TPU) as a polymer and carbon black (CB), Ag-powder, multi-walled carbon nanotubes (MWCNTs), which are widely used as electrically conducting nanofillers. After applying the fiber to the heat drawing process at different draw ratios, the filler volume fraction, linear density, breaking to strength, and electrical conductivity according to each draw ratio and volume fraction. In addition, scanning electron microscopy (SEM) images were taken. The breaking to strength of the TPU fiber containing the nanofillers increased with increasing draw ratio. At a draw ratio of 2.5, the breaking to strength of the TPU fiber increased by 105 % for neat-TPU, 88 % for CB, 86 % for Ag-powder, and 127 % for MWCNT compared to the undrawn fiber. The breaking to strength of the TPU fiber containing CB decreased gradually with increasing volume fraction, and in case of Ag-powder, it decreased sharply owing to its specific gravity. The electrical conductivity of the TPU fiber containing CB and Ag-powder decreased with increasing draw ratio, but the electrical conductivity of the TPU fiber containing MWCNT increased rapidly after the addition of 1.34 vol. % or over. The moment when the aggregation of MWCNT occurred and its breaking to strength started to decrease was determined to be the percolation threshold of the electrical conductivity. The heat drawing process of the fiber-form material containing the anisotropic electrical conductivity nanofillers make the percolation threshold of the electrical conductivity and the maximum breaking to strength appear at a lower volume fraction. This is effective in the development of a breaking to strength and electrical conductivity.     

小箬棕种子活力在成熟过程中的变化

研究了小箬棕(Corypha minor Jacq.)种子成熟过程中含水量、种子活力、电导率及POD活性的变化。结果表明,在种子成熟过程中,含水量从47%下降到21%,当含水量为25%时(即黑色期)种子活力最高。黑色期是种子发育成熟期,该阶段种子的POD活性最高、电导率最低。黑色期后的种子活力及其它生理功能较大幅度降低。     

Fabrication of homogeneous multi-walled carbon nanotube/poly (vinyl alcohol) composite films using for microwave absorption application

Poly (vinyl alcohol) (PVA)/multi walled carbon nanotubes (MWNT) nanocomposite films were fabricated and their microwave absorption behavior were evaluated using vector network analyzer in the frequency range of 8–12 GHz (Xband). The uniform, stable dispersion and well oriented MWNT within the PVA matrix were achieved through using sodium dodecyl sulfate (SDS) as dispersing agent. The surface morphology of the PVA/SDS/MWNT films was examined by scanning electron microscope (SEM). The SEM analysis of the film samples revealed the uniform appearance in the whole surfaces of the fabricated composite films. However, some roughness on the surface was observed due to the presence of MWNT in the film structure. The PVA/SDS/MWNT films show significant increase in microwave absorption which is improved by increasing the MWNT content. The PVA/SDS/MWNT nanocomposite film sample with MWNT loading of 10 wt% showed the maximum and the relatively high microwave absorption of 28.00 dB at the frequency of 8.6 GHz.     

Electrically conductive and hydrophobic cotton fabrics by polypyrrole-oleic acid coating

Hydrophobic polypyrrole-coated fabrics with improved electrical conductivity were produced embedding oleic acid as counter-ion. Hydrophobisation of polypyrrole was carried out by means of an ion exchange process after deposition of polypyrrole on cotton fabrics. The fabrics coated with oleic acid-doped polypyrrole showed contact angle of 111°, drop absorption time of 7 minutes and high water repellence, while electrical conductivity increased of ～2 times and heat generation improved, too. Moreover, oleic acid demonstrated a great stability as counter-ion in polypyrrole matrix being present also after washing.     

Composites of polyvinyl alcohol and carbon nanotubes decorated with silver nanoparticles

A simple method to decorate carbon nanotubes (CNTs) with silver nanoparticles was developed to enhance the electrical conductivity of CNTs. The acid-treated CNTs were suspended in the silver acetate solution, ammonia solution was then added, and the CNTs decorated with silver nanoparticles (Ag@CNTs) were produced. The Ag@CNTs were dispersed in polyvinyl alcohol (PVA) to fabricate electrically conducting polymer composites. The electrical, thermal and mechanical properties of the composites were measured. The electrical conductivity of the composites containing 0.8 % (o.w.f.) Ag@CNTs was more than four orders of magnitude higher than those of pristine and functionalized CNTs respectively, which confirmed the effectiveness of the Ag@CNTs as conducting filler. However, the improved electrical conductivity led to somewhat decrease of mechanical properties of PVA/Ag@CNTs composites.     

Effect of solvent and blended polymer on electrical conductivity of PEDOT:PSS/polymer blended nanofibers

Poly(3,4-ethylenedioxythiophene)/poly(styrene sulfonate) (PEDOT:PSS) and polyethylene oxide (PEO) (or polyvinyl alcohol (PVA)) blended electrospun nanofibers were prepared in the presence of dimethyl sulfoxide (DMSO) and ethylene glycol (EG). The effects of added solvents (DMSO and EG) and blended polymers (PEO and PVA) on electrical conductivity and current-voltage (I-V) response were investigated. Electrical conductivity was dependent on both the additional solvent and blended polymers. PEDOT:PSS/PEO blended nanofibers showed a much higher electrical conductivity than PEDOT:PSS/PVA. EG blended PEDOT:PSS/PEO blended nanofibers showed much higher electrical conductivity than DMSO. The PEDOT:PSS/PEO/EG blended nanofibers web showed the highest value in I-V response.     

Polyester-based thermoplastic elastomer/MWNT composites: Rheological, thermal, and electrical properties

Polyester-based thermoplastic elastomer (Hytrel®) was melt-compounded with multi-walled nanotubes (MWNTs) using an internal mixer and the changes in the thermal, electrical and rheological properties were investigated using a range of nanotube contents (from 0.1 to 7 wt%). Even at nanotube concentrations as low as 0.1 wt%, the crystallization temperature was remarkably elevated by 15 °C and it increased further up to 22 °C with a 5 wt% loading. On the contrary, the melting temperature increased by 2 °C with 0.1 wt% MWNTs and it was slightly decreased by further additions of MWNTs. Electrical conductivity measured by the four probe method was detected from the 1 wt% MWNTs, indicative of electrical percolation. In addition, MWNTs starting from 4 wt% and above had no significant effect on the electrical conductivity, while it rapidly increased with nanotube contents below 4 wt%. Dynamic rheological properties were measured using a strain controlled rotational rheometer. The complex viscosity increased with MWNT contents giving an abrupt increase between 0.5 and 1 wt% loadings. In addition, the storage and loss modulus increased in a different manner depending on the range of the nanotube concentration. In the Cole-Cole plot, the slope of the nanocomposites decreased from 1.63 to 0.74 with increasing nanotube contents. In the Casson plot, the addition of MWNTs up to 0.5 wt% did not show any yield behavior giving an extremely low value for the yield stress, but further additions of nanotubes increased it notably. The presence of nanotubes in the elastomer increased the relaxation time with nanotube contents and their effect became weak as the frequency increased.     

不同类型玉米种子活力检测适宜方法的研究

以3种不同类型(普通玉米、糯玉米、甜玉米)共6个品种的玉米种子为试验材料,采用了标准发芽、电导率测定、TTC定量测定、丙二醛含量测定活力检测方法,对人工老化获得的不同类型玉米不同活力水平的种子进行了各项活力指标的测定,以确定不同类型玉米种子活力检测的适宜指标和方法。结果表明:普通玉米种子活力检测的适宜方法为标准发芽试验、电导率测定试验;糯玉米种子活力检测的适宜方法为标准发芽试验、丙二醛含量测定试验;甜玉米种子活力检测的适宜方法为标准发芽试验、电导率测定试验。