We report that chlorosulfonic acid is a true solvent for a wide range of carbon nanotubes (CNTs), including single-walled (SWNTs), double-walled (DWNTs), multiwalled carbon nanotubes (MWNTs), and CNTs hundreds of micrometers long. The CNTs dissolve as individuals at low concentrations, as determined by cryo-TEM (cryogenic transmission electron microscopy), and form liquid-crystalline phases at high concentrations. The mechanism of dissolution is electrostatic stabilization through reversible protonation of the CNT side walls, as previously established for SWNTs. CNTs with highly defective side walls do not protonate sufficiently and, hence, do not dissolve. The dissolution and liquid-crystallinity of ultralong CNTs are critical advances in the liquid-phase processing of macroscopic CNT-based materials, such as fibers and films.
We demonstrate a simple one-step method for synthesizing noble metal nanoparticle embedded free standing polydimethylsiloxane (PDMS) composite films. The process involves preparing a homogenous mixture of metal salt (silver, gold and platinum), silicone elastomer and the curing agent (hardener) followed by curing. During the curing process, the hardener crosslinks the elastomer and simultaneously reduces the metal salt to form nanoparticles. This in situ method avoids the use of any external reducing agent/stabilizing agent and leads to a uniform distribution of nanoparticles in the PDMS matrix. The films were characterized using UV-Vis spectroscopy, transmission electron microscopy and X-ray photoemission spectroscopy. The nanoparticle-PDMS films have a higher Young's modulus than pure PDMS films and also show enhanced antibacterial properties. The metal nanoparticle-PDMS films could be used for a number of applications such as for catalysis, optical and biomedical devices and gas separation membranes.
This study demonstrates the formation of a flexible and free-standing carbon nanotube-copper oxide-poly(vinylidene fluoride) (CNT-Cu(2) O-PVDF) nanocomposite and its application as an electrode-separator material for Li-ion batteries. Binder-free hybrid electrodes are obtained by conformally coating CNTs with Cu(2) O via electrodeposition and then embedding the resulting architecture into a porous poly(vinylidene fluoride-hexafluoropropylene) PVDF-HFP-SiO(2) polymer electrolyte membrane. The synergistic presence of high-capacity transition metal oxides and conductive CNTs results in twice the reversible areal capacity of 2.3 mAh cm(-2) as compared to 1.2 mAh cm(-2) for pure CNTs.
The adhesion and friction behavior of soft materials, including compliant brushes and hairs, depends on the temporal and spatial evolution of the interfaces in contact. For compliant nanofibrous materials, the actual contact area individual fibers make with surfaces depends on the preload applied upon contact. Using in situ microscopy observations of preloaded nanotube hairs, we show how nanotubes make cooperative contact with a surface by buckling and conforming to the surface topography. The overall adhesion of compliant nanohairs increases with increasing preload as nanotubes deform and continuously add new side-wall contacts with the surface. Electrical resistance measurements indicate significant hysteresis in the relative contact area. Contact area increases with preload (or stress) and decreases suddenly during unloading, consistent with strong adhesion observed for these complaint nanohairs.
In this investigation, the effect of Zr substitution at the Ti site of the CaCu3Ti4O12 on the electrical properties has been studied. Samples with composition x = 0.00, 0.10 and 0.30 have been synthesized by the solid state ceramic route in the system CaCu3Ti4−xZrxO12. Powder x-ray diffraction data showed the formation of a single phase solid solution. The structure remains cubic similar to an undoped sample. The Seebeck coefficient, α, is measured on a thick pellet in the temperature range 500–800 K and is found to be negative in this temperature range, indicating n-type conduction in the temperature range of measurement. Dc resistivity, ρdc, and ac conductivity, σac, were measured to understand the mechanism of conduction. Immittance analysis is used to separate the contributions of the grains and grain boundaries to the total observed resistance. From the temperature and frequency dependence of ac conductivity, it is concluded that at and around room temperature conduction occurs due to thermally activated rotation of dipoles while at high temperature it occurs due to excitation of charge carriers at the conduction band edge and hopping at energies close to it. From the immittance analysis it is observed that activation energies of conduction for grains and grain boundaries are almost equal indicating the same mechanism of conduction.
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