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The elastomeric composites using styrene butadiene rubber (SBR) as the polymeric matrix with two types of carbon nanofillers, carbon black and carbon nanotubes, are prepared by melt mixing with the aim to use them as sensors of organic gases for monitoring industrial environments. The prepared composites contain various amounts of conducting nanofillers and are cross-linked before examination for gas sensing. The electrical conductivity of the prepared composites is measured and the percolation threshold is calculated for both types of composites. The first aim is to determine compositions slightly above the percolation threshold for later testing of the sensing properties. Swelling/deswelling experiments have also been performed. The dispersion of conducting fillers in SBR matrix is studied by scanning and transmission electron microscopy techniques, and the mechanical properties of the pure matrix and all prepared composites are determined by tensile testing. Three organic gases, toluene, tetrahydrofuran, and n-hexane, in various mixtures with air are used to examine the ability of the prepared composites to react in their presence by changing the electrical properties. Cyclability of the sensing performance of the composites is also examined. Sensing results reveal the suitability of the prepared SBR-based materials as sensors for harmful solvents and gases widely used in industry. [ABSTRACT FROM AUTHOR]

Five different polypyrroles (PPys) with four different oxidants, namely, FeCl 3 , FeCl 3 ·6H 2 O, Fe 2 (SO 4 ) 3 , and (NH 4 ) 2 S 2 O 8 , were prepared by chemical oxidative polymerization and studied during aging. In the case of FeCl 3 , the anionic surfactant dodecylbenzenesulfonic acid (DBSA) was used as a co-dopant to improve the stability. The prepared PPys were aged (>400 days) in ambient air at a temperature of 24 ± 2 °C in our laboratory, where they were not directly exposed to the sun. A clear increase in the oxygen content could be seen on the surface of all the prepared samples. There was no significant difference between PPy prepared using FeCl 3 and FeCl 3 ·6H 2 O as oxidants. The incorporation of the anionic surfactant dodecylbenzenesulfonic acid into the PPy structure did not lead to a longer effective conjugation length but did lead to the superior stability of the prepared PPy in ambient air. PPy prepared with Fe 2 (SO 4 ) 3 and (NH 4 ) 2 S 2 O 8 showed inferior stability of electrical conductivity among the samples studied. The samples were characterized by X-ray photoelectron spectroscopy (XPS), Fourier transformed infrared spectroscopy (FTIR), and elemental analysis (EA), and the chemical changes during aging were confronted with measurements of the electrical conductivity. [ABSTRACT FROM AUTHOR]

Multiwalled carbon nanotubes (CNT) were modified via the non-covalent approach using anodic surfactants dodecylbenzenesulfonic acid (DBSA) and poly(ethylene glycol) n-alkyl 3-sulfopropyl ether potassium salt and cationic surfactant cetyltrimethylammonium bromide (CTAB). These surfactants were used individually or as DBSA/CTAB mixtures. Surface modification was ultrasonically-assisted with a control over sonication power (64 or 360 W). The surface properties of modified CNT particles were determined by X-ray photoelectron spectroscopy and scanning electron microscopy. The electrical conductivities of unmodified CNT, particles treated by ultrasound, and CNT modified with surfactants were measured. Thermogravimetric analysis was used to determine the mass loading of surfactants after drying. The highest increase in conductivity was reached when CNT were treated solely with the anionic surfactant DBSA under the influence of soft ultrasound. This work shows conclusively that ultrasound-assisted modification of CNT by surfactants is a simple and efficient approach to prepare surface modified and highly conductive CNT, provided that physical (ultrasonic) and chemical (surfactants) treatments are concomitantly controlled. [ABSTRACT FROM AUTHOR]

The effect of ionic surfactants and manufacturing methods on the separation and distribution of multi-wall carbon nanotubes (CNTs) in a silicone matrix are investigated. The CNTs are dispersed in an aqueous solution of the anionic surfactant dodecylbenzene sulfonic acid (DBSA), the cationic surfactant cetyltrimethylammonium bromide (CTAB), and in a DBSA/CTAB surfactant mixture. Four types of CNT-based composites of various concentrations from 0 to 6 vol.% are prepared by simple mechanical mixing and sonication. The morphology, electrical and thermal conductivity of the CNT-based composites are analyzed. The incorporation of both neat and modified CNTs leads to an increase in electrical and thermal conductivity. The dependence of DC conductivity versus CNT concentration shows percolation behaviour with a percolation threshold of about 2 vol.% in composites with neat CNT. The modification of CNTs by DBSA increases the percolation threshold to 4 vol.% due to the isolation/separation of individual CNTs. This, in turn, results in a significant decrease in the complex permittivity of CNT-DBSA-based composites. In contrast to the percolation behaviour of DC conductivity, the concentration dependence of thermal conductivity exhibits a linear dependence, the thermal conductivity of composites with modified CNTs being lower than that of composites with neat CNTs. All these results provide evidence that the modification of CNTs by DBSA followed by sonication allows one to produce composites with high homogeneity [ABSTRACT FROM AUTHOR]

Abstract: Polypropylene (PP) and viscose (VS) textiles were modified by the in situ synthesis of a conducting polypyrrole (PPy) overlayer. To improve adhesion of the conducting layer to the textile surface, a pyrrole-functionalized silane (SP) was synthesized and bonded onto the surface before polypyrrole formation. Moreover, to introduce hydroxyl groups into the surface, PP was pretreated by grafting vinyltrimethoxysilane by means of a radiofrequency plasma discharge. The study is focused on the influence of SP on the washing fastness of a PPy layer and, consequently, on the overall conductivity of the textiles after washing. In the case of viscose, PPy was found to penetrate the substrate. A compromise was found between the influence of SP and penetration phenomenon (best conductivity after washing: wVS–0.2SP/25Py=3×10−5 S/square). In the case of polypropylene the effect of pretreatment with SP is much better than for viscose, and a higher concentration of SP leads to improved fastness of the conductive layer (wmPP–0.2SP/25Py=3×10−5 S/square; wmPP–1SP/25Py=8×10−5 S/square), which indicates that the coating promoted by means of SP is more favoured than for viscose. [Copyright &y& Elsevier]