Polyaniline and their Conductive Polymer Blends: A Short Review

This short review discusses recent research regarding conductive polymeric blends containing polyaniline (PANI). Conducting PANI was reviewed in view of their properties to be used as a conducting component in several polymer matrix composites. Conductive PANI blends shows promise since the discovery of conducting polymers itself. These composite materials have introduced practical applications in various fields, including electromagnetic shielding and microwave absorption, static electricity dissipation, conducting membrane materials, conductive paint coatings and sensor materials. Highlights were made on PANI containing composites of polyethylene, polyamides, rubbers and elastomers, including other conventional thermoplastics and thermosets. Their electrical properties (percolation threshold and resistivity), blends preparation, drawbacks and potential usage were discussed in detail.

SPPO/PEI-based acid-base blend membranes for direct methanol fuel cells

New acid-base polymer blends based on sulfonated poly(phenylene oxide) (SPPO) as the proton-conducting component and poly(ether imide) (PEI) as the basic component were considered for use as proton-exchange membranes (PEM). The obtained blend membranes had a higher thermal stability and a higher glass transition temperature (Tg) than the pure SPPO, as revealed by TGA and DSC. The morphology of blend membranes indicated that PEI was highly compatible with SPPO polymers because of the formation of hydrogen bonds between the sulfonated acid and PEI. Although the blend membranes exhibited a lower water uptake and lower proton conductivity than the pure SPPO membrane, the PEI component improved the dimensional stability, mechanic properties, and especially inhibited methanol permeation. The methanol permeability coefficient of the blend membrane with 30 wt.% PEI content was 9.68×10-8 cm2/s, which is lower than that of the pure SPPO and just one tenth of that of Nafion® 112. This considerable reduction in methanol crossover revealed the feasibility of the blend membranes as promising electrolytes for direct methanol fuel cells.

Contribution of Fast and Slow Conducting Myelinated Axons to Single-Peak Compound Action Potentials in Rat Spinal Cord White Matter Preparations

Unlike recordings derived from optic nerve or corpus callosum, compound action potentials (CAPs) recorded from rodent spinal cord white matter (WM) have a characteristic single-peak shape despite the heterogeneity of axonal populations. Using a double sucrose gap technique, we analyzed the CAPs recorded from dorsal, lateral, and ventral WM from mature rat spinal cord. The CAP decay was significantly prolonged with increasing stimulus intensities suggesting a recruitment of higher threshold, slower conducting axons. At 3.5 mm conduction distance, a hidden higher threshold, slower conducting component responsible for prolongation of CAP decay was uncovered in 22 of 25 of dorsal WM strips by analyzing the stimulus-response relationships and a normalization-subtraction procedure. This component had a peak conduction velocity (CV) of 5.0 ± 0.2 (SE) m/s as compared with 9.3 ± 0.5 m/s for the lower threshold peak ( P < 0.0001). Oxygen-glucose deprivation (OGD), along with its known effects on CAP amplitude, significantly ( P < 0.015) shortened the CAP decay. The hidden higher threshold, slower conducting component showed greater sensitivity to OGD compared with the lower threshold, faster conducting component, suggesting a differential sensitivity of axonal populations of spinal cord WM. At longer conduction distances and lower temperatures (9.8 mm, 22–24°C), the slower peak could be directly visualized in CAPs at higher stimulation intensities. A detailed analysis of single-peak CAPs to identify their fast and slow conducting components may be of particular importance for studies of axonal physiology and pathophysiology in small animals where the conduction distance is not sufficiently long to separate the CAP peaks.

Clustering of C-Terminal Stromal Domains of Tha4 Homo-oligomers during Translocation by the Tat Protein Transport System

The chloroplast Twin arginine translocation (Tat) pathway uses three membrane proteins and the proton gradient to transport folded proteins across sealed membranes. Precursor proteins bind to the cpTatC-Hcf106 receptor complex, triggering Tha4 assembly and protein translocation. Tha4 is required only for the translocation step and is thought to be the protein-conducting component. The organization of Tha4 oligomers was examined by substituting pairs of cysteine residues into Tha4 and inducing disulfide cross-links under varying stages of protein translocation. Tha4 formed tetramers via its transmembrane domain in unstimulated membranes and octamers in membranes stimulated by precursor and the proton gradient. Tha4 formed larger oligomers of at least 16 protomers via its carboxy tail, but such C-tail clustering only occurred in stimulated membranes. Mutational studies showed that transmembrane domain directed octamers as well as C-tail clusters require Tha4's transmembrane glutamate residue and its amphipathic helix, both of which are necessary for Tha4 function. A novel double cross-linking strategy demonstrated that both transmembrane domain directed- and C-tail directed oligomerization occur in the translocase. These results support a model in which Tha4 oligomers dock with a precursor–receptor complex and undergo a conformational switch that results in activation for protein transport. This possibly involves accretion of additional Tha4 into a larger transport-active homo-oligomer.

The AC and DC Conductivity of Nanocomposites

The microstructures of binary (conductor-insulator) composites, containing nanoparticles, will usually have one of two basic structures. The first is the matrix structure where the nanoparticles (granules) are embedded in and always coated by the matrix material and there are no particle-particle contacts. The AC and DC conductivity of this microstructure is usually described by the Maxwell-Wagner/Hashin-Shtrikman or Bricklayer model. The second is a percolation structure, which can be thought to be made up by randomly packing the two types of granules (not necessarily the same size) together. In percolation systems, there exits a critical volume fraction below which the electrical properties are dominated by the insulating component and above which the conducting component dominates. Such percolation systems are best analyzed using the two-exponent phenomenological percolation equation (TEPPE). This paper discusses all of the above and addresses the problem of how to distinguish among the microstructures using electrical measurements.

Effective Medium Theory of Dielectric Constant of Granular Materials in the Presence of Skin Effect

We consider the behavior of the dielectric constant of percolation composite systems. An example of such systems is a composite material consisting of a disordered mixture of metallic and insulating particles. A reduction in concentration P of the metallic (conducting) component reduces the static conductivity of the composite, so that it vanishes at some critical concentration PC known as the percolation threshold.

On Experimental Data of the TCR of TFRs and Their Relation to Theoretical Models of Conduction Mechanism

Any theory of electrical conduction in TFRs encounters mainly two problems: (i) explanation of the dependence of R□on properties of conducting component (volume fraction, grain size, resistivity), (ii) explanation of the temperature dependence of R□taking into account (i). In order to achieve this one has to fit some microscopic parameters to experimental R□-and TCR-values, and to check if they are reasonable or not. The aim of the following discussion is to show, that such a fitting by means of experimental TCR-values is not correct. This is due to the fact that TCR-behaviour, as is well known, is determined also by the dependence of resistivity on strain. But any theoretical model neglects strains, also those who are induced by thermal strains. By means of published experiments concerning the strain dependence of resistance, the magnitude is estimated by which the TCR-values have to be corrected for the described fit.