We show that single-wall carbon nanotube (SWNT) fibers produced by the particle-coagulation spinning process possess a well-developed hierarchical skin−core structure. Primary SWNTs are organized in bundles that are 10−30 nm in diameter. The nanotube bundles form elementary filaments, which constitute the fiber skin, and a highly porous nanofelt, which fills the fiber core. The elementary filaments of ∼0.2−2 µm diameter are well aligned along the fiber axis and densely packed. The hierarchical pore structure organization determines unique wetting and sorption properties of SWNT fibers. Experiments with capillary condensation and droplet absorption of wetting fluids agree with the proposed skin−core model and can be used for pore structure characterization. The well-developed porosity and high surface area in conjunction with controllable electrical and mechanical functionalities make the SWNT fibers attractive materials for nanotechnologies, where wetting and sorption properties play an important role.

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We describe a phenomenon of ribbon-to-fiber transformation observed in the process of spinning of single wall carbon nanotubes dispersed in polymer solutions. In the process of spinning, a gel-like ribbon comprised of nanotube bundles bound by polymer is withdrawn from a solvent bath. We show that upon crossing the liquid-air interface, the ribbon may either retain its flat shape or fold into a compact hairlike fiber. The ribbon-to-fiber transformation is caused by the capillary action of the liquid meniscus embracing the ribbon. Only sufficiently stiff ribbons can withhold the capillary compression. The critical conditions of folding, as well as the number of folds in the contractive ribbon, depend on the ribbon width, its flexural rigidity, and the solvent surface tension. We show that the ribbon rigidity can be efficiently modulated by varying the solvent composition, allowing us to control the pore structure of carbon-nanotube fibers.

Structure development during drawing was studied for three sets of polyamide‐66 (PA66) fibers with density, optical microscopy, wide‐angle X‐ray diffraction, and Fourier transform infrared spectroscopy. The crystallinity, estimated by density measurements, remained virtually constant with increasing draw ratios, indicating that stress‐induced crystallization did not occur for the PA66 fibers drawn at room temperature, but there was a rapid transformation from a hedrite morphology to a fibrillar one. The absence of stress‐induced crystallization differed from the behavior of polyamide‐6, and this was attributed to the stronger hydrogen bonding between polyamide chains and the higher glass‐transition temperature of PA66. Polarized infrared spectroscopy was used to measure the transition‐moment angles of the vibrations at 936 and 906 cm−1, which were found to be 48 and 60°, respectively. The crystalline orientation was estimated from the band at 936 cm−1, and the increase with an increasing draw ratio was in close quantitative agreement with X‐ray diffraction data; this showed that infrared spectroscopy could be used reliably to measure the crystalline orientation of PA66 fibers. Because we were unable to obtain the transition‐moment angle of the amorphous bands, the amorphous orientation was obtained with Stein's equation. The amorphous orientation developed more slowly than the crystalline orientation, which is typical behavior for flexible‐chain polymers. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 1940–1948, 2002

The effect of curling hair with a curling iron has been investigated. Possibilities of thermal damage with repeated curling according to, and in violation of, the manufacturer's specifications have been studied. The propensity of hair surface to damage depends on the moisture content of the hair, and these experiments have been conducted in both wet and dry conditions, with and without application of tension, and with short or prolonged times. Scanning electron microscopic examination revealed that fibers treated under the dry condition (50% RH) show radial and axial cracking along with scale edge fusion. Similar thermal treatment on wet hair resulted in severe damage of the type described above, as well as bubbling and buckling of the cuticle due to the formation and escaping of steam from the fiber. Fibers subjected to repeated curling in the dry condition show slight increases in tensile mechanical properties, characteristic of a cross‐linked fiber. Fibers treated with conditioners show an improvement in characteristic life, especially in the case of low‐molecular‐weight conditioners, such as CETAB, which can penetrate into the hair fiber (shown by TOF‐SIMS analysis).