|References using NanoLab nanotubes in composites and sensors, fuel cells|
1. Asa H. Barber, Sidney R. Cohen, Shmuel Kenig and H. Daniel Wagner. (2004, November). Interfacial fracture energy measurements for multi-walled carbon nanotubes pulled from a polymer matrix. Composites science and technology, Volume 64, Issue 15, Pages 2283-2289
Pullout experiments were performed at the nanoscale using an atomic force microscope, to assess the interfacial adhesion between multi-walled carbon nanotubes and a matrix of polyethylene–butene. Fracture energy for the nanotube–polymer interface was calculated from the measured pullout forces and embedded lengths. The results suggest the existence of a relatively strong interface, with higher fracture energy for smaller diameter nanotubes.
2. Yael Dror, Wael Salalha, Rafail L. Khalfin,Yachin Cohen, Alexander L. Yarin, and Eyal Zussman. Carbon nanotubes embedded in oriented polymer nanofibers by electrospinning.
Abstract: The electrospinning process was used successfully to fabricate nanofibers of poly(ethylene oxide) (PEO) in which multiwalled carbon nanotubes (MWCNT) are embedded. Initial dispersion of MWCNTs in water was achieved using amphiphiles, either as small molecules (sodium dodecyl sulfate, SDS) or as a high molecular weight, highly branched polymer (Gum Arabic). These dispersions provided separation of the MWCNTs and their individual incorporation into the PEO nanofibers by subsequent electrospinning. The focus of this work is on the development of axial orientations in these multicomponent nanofibers. A theoretical model is presented for the behavior of rodlike particles representing CNTs in electrospinning. Initially the rods are randomly oriented, but due to the sinklike flow in a wedge they are gradually oriented mainly along the stream lines, so that straight CNTs are almost oriented upon entering the electrospun jet. The degrees of orientation of polymer, surfactant, and MWCNT were studied using X-ray diffraction and transmission electron microscopy. Oriented ropes of the nanofibers were fabricated in a converging electric field by a rotating disk with a tapered edge. A high degree of alignment of PEO crystals was found in electrospun nanofibers containing only PEO, as well as PEO/SDS. The latter also exhibited a high degree of alignment of the SDS layers. The axial orientation of PEO and SDS is significantly reduced in MWCNT-containing nanofibers. Transmission electron microscopy (TEM) images indicated that the MWCNTs were embedded in the nanofibers as individual elements, mostly aligned along the fiber axis. Nevertheless, there are also many cases in which the nanotubes appear twisted, bent, or with other irregularities. Comparison of cryo-TEM images of vitrified MWCNT dispersions with TEM images of the raw nanotubes indicated that sonication during the dispersion process may be responsible for the irregularities observed in some of the nanotubes.
3. S M Vemuru1, R Wahi2, S Nagarajaiah1,2*, and P M Ajayan. Strain sensing using a multiwalled carbon nanotube film.
Abstract: The effectiveness of multiwalled carbon nanotubes (MWCNTs) as strain sensors is investigated. The key contribution of this paper is the study of real-time strain response at the macroscale of MWCNT film under tensile load. In addition, real-time voltage change as a function of temperature is examined. MWCNT films attached to a brass specimen by epoxy using vacuum bonding have been studied. The brass specimen is subjected to tensile loading, and voltage output from the MWCNT film is obtained using a four-point probe and a sensitive voltage measurement device. Experimental results show that there is a linear change in voltage across the film when subjected to tension, and the MWCNT film both fully recovers its unstressed state upon unloading and exhibits stable electromechanical properties. The effect of temperature on the voltage output of the nanotube film under no load condition is investigated. From the results obtained it is evident that MWCNT films exhibit a stable and predictable voltage response as a function of temperature. An increase in temperature leads to an increase in conductivity of the nanotube film. The study of MWCNT film for real-time strain sensing at the macroscale is very promising, and the effect of temperature on MWCNT film (with no load) can be reliably predicted.
4. Margo Plaado, Robert Matias Mononen, Rünno Lõhmus, Ilmar Kink and Kristjan Saal. Formation of thick dielectrophoretic carbon nanotube fibers.
Abstract: The aim of this work was to study the formation process of dielectrophoretic (DEP) carbon nanotube fibers (CNT-fibers) and characterize the fiber properties relevant to their technological applications. The fiber diameter was shown to increase when applied voltage was increased (up to 350 Vpp) and when retraction speed was decreased (down from 400 µm s − 1) in accordance with theoretical expectations. This paper represents the first demonstration of the formation of thick DEP CNT-fibers (up to ~ ∅0.4 mm). This is an intriguing result, as it expands the diversity of possible applications of the fibers and facilitates their characterization by analytical methods that require large quantities of the material. The performance of these thick fibers was as follows: a density of ~ 0.35 g cm − 3, a tensile strength of ~ 15 MPa, a Young's modulus of ~ 1 GPa, and an electrical resistivity of ~ 70 mΩ cm.
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