Search results for "CONDUCTIVITY"
showing 10 items of 1988 documents
Crystallization and melting of fractions of branched polyethylene
1983
Effects of the molecular weight on the crystallization behaviour of branched polyethylene become observable if isothermal crystallization is studied at temperatures near to the melting end. Crystallinities decrease with decreasing molecular weight. Thicknesses of lamellae grown during isothermal crystallization are independent of the molecular weight. They depend only on temperature. Compared to the effect of the branches polydispersity gives only a minor contribution to the broadening of the crystallization and melting range of low density polyethylene.
Electrical conductivity properties of expanded graphite-polycarbonatediol polyurethane composites
2014
Conductive polymer composites of segmented polycarbonatediol polyurethane and expanded graphite (EG) have been synthesized with different amounts of EG conductive filler (from 0 to 50 wt%). SEM, X-ray diffraction measurements, Fourier transform infrared and Raman spectroscopies demonstrated a homogeneous dispersion of the EG filler in the matrix. The dielectric permittivity of the composites showed an insulator to conductor percolation transition with increase in EG content. Significant changes in the dielectric permittivity take place when the weight fraction of EG is in the range 20–30 wt%. Special attention has been paid to the dependence of the conductivity on frequency, temperature and…
Dielectric Spectroscopy of Recycled Polylactide
2014
The effects of multiple mechanical recycling on amorphous polylactide (PLA) were simulated by means of five successive injection-grinding cycles. The influence of the induced thermo-mechanical degradation on the dielectric properties of PLA was analysed. The relaxation spectra were studied in terms of the complex dielectric permittivity (ε0 and ε00) and the dielectric loss tangent, tg(d) in the frequency range from 102 to 107 Hz over the temperature interval from 0 C to 140 C. It was possible to distinguish two relaxations zones, one at low temperatures and high frequencies (b relaxation) and another at higher temperatures and lower frequencies (a relaxation). The individual relaxations wer…
Thermal disorder and correlation effects in anti-perovskite-type copper nitride
2017
This work has been supported by the Latvian National Research Program IMIS2. The EXAFS experiment has been financed from the European Community's Seventh Framework Programme under grant agreement No. 226716 (Project I-20100098 EC). J.T. also gratefully acknowledges support from the National Science Foundation under the DMREF program Grant No. CHE-1534184.
Recent Progress in the Development of Composite Membranes Based on Polybenzimidazole for High Temperature Proton Exchange Membrane (PEM) Fuel Cell Ap…
2020
[EN] The rapid increasing of the population in combination with the emergence of new energy-consuming technologies has risen worldwide total energy consumption towards unprecedent values. Furthermore, fossil fuel reserves are running out very quickly and the polluting greenhouse gases emitted during their utilization need to be reduced. In this scenario, a few alternative energy sources have been proposed and, among these, proton exchange membrane (PEM) fuel cells are promising. Recently, polybenzimidazole-based polymers, featuring high chemical and thermal stability, in combination with fillers that can regulate the proton mobility, have attracted tremendous attention for their roles as PE…
Proton conductivity through polybenzimidazole composite membranes containing silica nanofiber mats
2019
The quest for sustainable and more efficient energy-converting devices has been the focus of researchers&prime
Low Conductive Electrodeposited Poly(2,5-dimethoxyaniline) as a Key Material in a Double Lateral Heterojunction, for Sub-ppm Ammonia Sensing in Humid…
2019
We present a new device called a double lateral heterojunction (DLH) as an ammonia sensor in humid atmosphere. It combines polyaniline derivatives in their poor conducting state with a highly conductive molecular material, lutetium bisphthalocyanine, LuPc2. Polyaniline and poly(2,5-dimethoxyaniline) are electrodeposited on ITO interdigitated electrodes, leading to an original device that can be obtained only by electrochemistry and not by other solution processing techniques. Both polymers lead to highly conducting materials that require a neutralization step before their coverage by LuPc2. While the device based on polyaniline shows ohmic behavior, the nonlinear I- V characteristics of the…
Anti-Arrhenian behaviour of conductivity in octanoic acid–bis(2-ethylhexyl)amine systems: a physico-chemical study
2015
Pure surfactant liquids and their binary mixtures, owing to the amphiphilic nature of the molecules involved, can exhibit nano-segregation and peculiar transport properties. The structural and dynamic properties of octanoic acid (OA)–bis(2-ethylhexyl)amine (BEEA) liquid mixtures at various compositions have been studied by Wide Angle X-ray Scattering (WAXS), 1H-NMR and broadband dielectric spectroscopy as a function of temperature. It was found that the self-assembly occurs via proton exchange between the OA COOH group and the BEEA NH one; such self-assembled local structures are affected anisotropically by a temperature increase so that the thermal dilatation is more marked in a direction …
Non-ideal mixing behavior in dibutyl phosphate-propylamine binary liquids: Dielectric and nuclear magnetic resonance investigations
2021
Abstract Owing to the amphiphilic nature of their constituent molecules, binary mixtures of pure liquid surfactants are usually characterized by enhanced nano-segregation and thus can exhibit interesting transport properties and complex macroscopic behavior. In this ambit it was recently shown by Turco Liveri et al. (J. Mol. Liq. 263 (2018) 274–281) at room temperature that mixtures of short aliphatic chains compounds, such as dibutyl phosphate (DBP) and n-propylamine (PA) liquids, due to their ability to allow for phosphate-to-amine proton transfer, display ionic liquid–like behavior with composition-dependent enhanced conductivity, viscosity, and magnetically-induced birefringence. To und…
Relaxation of electronic excitations in LiNbO3crystals
2001
Transient absorption both in stoichiometric and Mg doped congruent LiNbO was observed after pulsed electron beam excitation. The luminescence spectra and decay kinetics in these materials show different excitonic relaxation possibilities. The dependence on sample stoichiometry is also discussed.