We suggest a new reinforcing mechanism for carbon nanotube (CNT)/rubber compounds, based on a comparison of CNT reinforcement of natural rubber (NR) with that by carbon black (CB). The mechanical properties of the NR/CNT compounds were significantly higher, but the amount of bound rubber, an indication of the level of filler-rubber interaction, was lower than with CB. Moreover, the CNT-filled compounds showed a greater degree of strain-softening (Payne effect) and stresssoftening (Mullins effect) and higher permanent set than the CB-filled compounds, indicating weaker bonding. In scanning electron microscope studies on cryogenicallyfractured surfaces, the CNT bundles were seen to protrude out of the surface when the sample was stretched and slid back in when the deformation was removed. We infer that interfacial interactions between CNT and NR are weak in comparison with the relatively strong adhesion between rubber and CB, as indicated by the high amount of bound rubber in that case. Thus, reinforcement by CNTs is attributed to their large aspect ratio and physical entanglement with rubber molecules, rather than to strong interfacial interaction.
The colorimetric gas sensor offers an opportunity for the simple and rapid detection of toxic gaseous substances based on visually discernible changes in the color of the sensing material. In particular, the accurate detection of trace amounts of certain biomarkers in a patient's breath provides substantial clues regarding specific diseases, for example, hydrogen sulfide (H 2 S) for halitosis and ammonia (NH 3 ) for kidney disorder. However, conventional colorimetric sensors often lack the sensitivity, selectivity, detection limit, and mass-productivity, impeding their commercialization. Herein, we report an inexpensive route for the meter-scale synthesis of a colorimetric sensor based on a composite nanofiber yarn that is chemically functionalized with an ionic liquid as an effective H 2 S adsorbent and lead acetate as a colorimetric dye. As an eyereadable and weavable sensing platform, the single-strand yarn exhibits enhanced sensitivity supported by its high surface area and well-developed porosity to detect the breath biomarker (1 ppm of H 2 S). Alternatively, the yarn loaded with lead iodide dyes could reversibly detect NH 3 gas molecules in the ppm-level, demonstrating the facile extensibility. Finally, we demonstrated that the freestanding yarns could be sewn into patterned textiles for the fabrication of a wearable toxic gas alarm system with a visual output.
The interactions of carbon nanotubes (CNTs) and carbon black (CB) with rubber matrices are of great interest. Although both belong to the carbon filler family, their interactions are different. In this study the adhesion of CNTs, if any, with natural rubber (NR) was examined. Scanning electron microscopy examinations made on cryogenically fractured surfaces of a crosslinked NR sample containing 7% by weight of CNTs showed that the CNT bundles emerged from the side surface (narrowed by Poisson's ratio) and slowly slid back in when the deformation was removed. The protruded lengths were many times larger than the nanotube bundle diameters. This extensive slipping out of CNTs from the rubber matrix suggests that interfacial interactions between CNTs and NR are quite weak. In contrast, relatively strong interactions were found between CB and rubber, indicated by the large amount of bound rubber formation. Reinforcement of rubber by CNTs is therefore attributed to the large aspect ratio of CNT bundles. Physical entanglement with rubber molecules is then able to generate effective load transfer, replacing the strong adhesion found with CB. Copyright © 2010 Society of Chemical Industry
Polymer nanocomposites reinforced with multi-walled carbon nanotubes (MWCNTs) have been newly introduced for semiconducting layers of high-voltage electrical power cables. Homogeneity of the MWCNT-reinforced polymer nanocomposites was achieved by solution mixing, and their mechanical, thermal and electrical properties were investigated depending on the type of polymer. By changing the polymer matrix, the volume resistance of the MWCNT-reinforced polymer nanocomposites could be varied by more than four orders of magnitude. Through systematic experiments and analysis, two possible factors affecting the volume resistance were found. One is the degree of crystallinity of the polymer used and the other is the change of MWCNT morphology under strain. By increasing the degree of crystallinity above a certain level, the volume resistance linearly increased. The MWCNTs embedded in the nanocomposites gradually protruded through the surface on stretching the sample and reversibly returned back to the original positions at a relatively small strain (below 20%). Based on the criteria of tensile properties and volume resistance, a poly[ethylene-co-(ethyl acrylate)]/MWCNT nanocomposite was selected as the best candidate for the semiconducting layers of high-voltage electrical power cables.
For the immediate detection of gaseous strong acids, it is advantageous to employ colorimetric textile sensors based on halochromic dyes. Thus, a rhodamine dye with superior pH sensitivity and high thermal stability was synthesized and incorporated in nylon 6 and polyester fabrics to fabricate textile sensors through dyeing and printing methods. The spectral properties and solubility of the dye were examined; sensitivity to acidic gas as well as durability and reversibility of the fabricated textile sensors were investigated. Both dyed and printed sensors exhibited a high reaction rate and distinctive color change under the acidic condition owing to the high pH sensitivity of the dye. In addition, both sensors have outstanding durability and reversibility after washing and drying.
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