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Maximum Conductivity (maximum + conductivity)
Selected AbstractsAnhydrous Polymeric Proton Conductors Based on Imidazole Functionalized PolysiloxaneFUEL CELLS, Issue 3-4 2006G. Scharfenberger Abstract Intrinsically proton conducting polymers with imidazole as proton solvent tethered to a polysiloxane backbone via a flexible spacer have been synthesized. Apart from the standard characterization also their thermal properties and transport behavior have been investigated. The materials exhibit proton conductivity as a consequence of self-dissociation of the imidazole moieties and "structure diffusion" of the resulting defects. In particular, no liquid phase such as water or monomeric imidazole is needed for the observed proton conductivities. To study the influence of the tether structure on the transport properties, cyclic oligomers and open chain polymers with different spacer lengths have been synthesized. The materials are thermally stable up to 200,°C and become soft around room temperature. The conductivity exhibits VTF and WLF behavior with maximum conductivities around ,,=,1.5.10,3,S,cm,1 at T,=,160,°C. The activation volume of the conductivity as derived from pressure dependent measurements is found to be unusually high. The lowest activation volumes and the highest conductivities are observed for the materials with the highest segmental mobilities, i.e. the longest spacers. Proton self-diffusion coefficients as obtained from PFG NMR diffusion measurements are significantly higher than expected from the proton conductivities obtained by dielectric spectroscopy. This corresponds to unusually high Haven ratios which have been interpreted by correlated proton transfers allowing for fast proton diffusion while minimizing the separation of ionic charge carriers. [source] Synthesis and characterization of new unsaturated polyesters containing cyclopentapyrazoline moiety in the main chainJOURNAL OF APPLIED POLYMER SCIENCE, Issue 6 2010Ismail A. Alkskas Abstract 3-p -Hydroxyphenyl-6- p -hydroxybenzylidene cyclopentapyrazoline (III) and 3-vanillyl-7-vanillylidene cyclopentapyrazoline (IV) were used as new starting materials for preparing new unsaturated polyesters. The polyesters were prepared by reacting (III) or (IV) with adipoyl, sebacoyl, isophthaloyl, and terephthaloyl dichlorides utilizing the interfacial polycondensation technique. The polyester samples have been characterized by elemental and spectral analyses. The polyesters have inherent viscosities of 0.55,0.97 dL/g. All the polyesters are semicrystalline and most of them are partially soluble in most common organic solvents but freely soluble in concentrated sulfuric acid. Their glass transition temperatures (Tg) range from 103.34 to 208.81°C, and the temperatures of 10% weight loss as high as 190 to 260°C in air, indicating that these aromatic polyesters have high Tg and excellent thermal stability. Doping with iodine dramatically raised the conductivity and produced dark brown colored semiconductive polymers with a maximum conductivity in the order of 3.1 × 10,7 ,,1 cm,1. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010 [source] Conductivity and characterization of polyurea electrolytes with carboxylic acidJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 24 2003Shao-Ming Lee Abstract Polyurea, which was synthesized from 4,4,-diphenylmethane diisocyanate, Jeffamine-ED2001 (weight-average molecular weight: 2000), and 3,5-diaminobanzoic acid (DABA) were doped with lithium perchlorate (LiClO4) as the polyelectrolyte. Differential scanning calorimetry (DSC), Fourier transform infrared (FTIR) spectroscopy, and 7Li magic-angle spinning (MAS) solid-state NMR were used to monitor changes in the morphology of polyurea electrolytes corresponding to the concentration of LiClO4 dopants. DSC showed the glass-transition temperature of the hard and soft segments increases with salt concentration. FTIR indicated the carboxylic group of DABA coordinates with the Li+ ion, and the ordered hydrogen-bonded urea carbonyl groups are destroyed when the salt concentration exceeds 0.5 mmole of LiClO4 (gPUrea),1. The 7Li MAS solid-state NMR investigation of the polyurea electrolytes revealed the presence of two Li+ environments at lower temperature. Impedance spectroscopy measurements showed that the conductivity behavior followed the Arrhenius equation, and the maximum conductivity occurred when the crystalline structure of polyurea was disrupted. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 4007,4016, 2003 [source] Thermal and Electric Properties in Hot-Pressed ZrB2,MoSi2,SiC CompositesJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 7 2007Shuqi Guo The thermal and electrical properties of MoSi2 and/or SiC-containing ZrB2 -based composites and the effects of MoSi2 and SiC contents were examined in hot-pressed ZrB2,MoSi2,SiC composites. The thermal conductivity and electrical conductivity of the ZrB2,MoSi2,SiC composites were measured at room temperature by a nanoflash technique and a current,voltage method, respectively. The results indicate that the thermal and electrical conductivities of ZrB2,MoSi2,SiC composites are dependent on the amount of MoSi2 and SiC. The thermal conductivities observed for all of the compositions were more than 75 W·(m·K),1. A maximum conductivity of 97.55 W·(m·K),1 was measured for the 20 vol% MoSi2 -30 vol% SiC-containing ZrB2 composite. On the other hand, the electrical conductivities observed for all of the compositions were in the range from 4.07 × 10,8.11 × 10 ,,1·cm,1. [source] Large Enhancement in Conductivity of Polyaniline Films by Cold StretchingMACROMOLECULAR CHEMISTRY AND PHYSICS, Issue 10 2010Hong-Mei Xiao Abstract The hot-stretching method has been well accepted for enhancing the electrical conductivity of conducting polymer films. High temperature is the prerequisite to soften the polymer to highly align and elongate the polymeric molecular chains. In this study, the cold-stretching method is proposed for the first time to enhance the conductivity of conducting polymeric films. Polyaniline (PANI) films are stretched at room temperature to different strain levels. It is observed that the applied strain has significant effects on the morphology, molecular chain structure, crystallinity, and crosslinking of the PANI films. As a result, the conductivity of PANI films is effectively increased by the cold-stretching process. Particularly, a maximum conductivity with an 18.4-fold increase in the direction parallel to the stretched direction is obtained when the elastic limit strain is applied. Compared to hot stretching, cold stretching is unique due to the extremely low dimensional change and very high efficiency achieved. [source] Ionic conductivity in poly (L-leucine)1,3-diamino propane,lithium iodide solid polymer electrolytePOLYMERS FOR ADVANCED TECHNOLOGIES, Issue 3 2009N. H. Kaus Abstract The pelletized Poly(L-Leucine)-1,3-diamino propane,lithium iodide (LiI) samples have been prepared by using a low temperature sintering method. Results from impedance spectroscopy have proven this mixture to be a superionic material with maximum conductivity obtained in the range of 10,3,S/cm for the samples containing 50,wt% LiI. The high ionic conductivity achieved was due to the increased number of charge carrier from LiI. Improved conductivity could also be due to hopping of lithium ion through the side chain of polymer. Infrared spectroscopy showed that both LiI and poly amino acid may co-exist together. From the spectra it is revealed that the CO band at 1643,cm,1 shifted to higher wave number indicating that chelation of Li+ may have occurred at oxygen atom. Results from X-ray diffraction show that the prepared samples were partially crystalline in nature. Some of the peaks have disappeared and this confirmed that some complexation has occurred within the sample. Copyright © 2009 John Wiley & Sons, Ltd. [source] | ||||||||||