We investigate the liquid crystal (LC) phase behaviors of the sodium cholate stabilized single-walled carbon nanotube (SWCNT) aqueous dispersions with different SWCNT aspect ratios. The isotropic-to-nematic phase transition occurs at a lower concentration for the SWCNT dispersion with larger aspect ratio, which is expected by the Onsager theory. The well-aligned film is successfully fabricated from the dispersion with the a higher SWCNT aspect ratio by the simple blade coating. We also prepare the SWCNT dispersions with different surfactants, sodium deoxycholate and sodium taurodeoxycholate, changing the surface condition of SWCNTs, which may affect the LC transition concentrations.

Controlling the alignment of single-walled carbon nanotubes (SWCNTs) on the macroscopic scale is critical for practical applications because SWCNTs are extremely anisotropic materials. One efficient technique is to create an effective SWCNT dispersion, which shows a liquid crystal (LC) phase. A strong acid treatment can realize SWCNT liquid crystalline dispersions. However, strong acids pose a substantial safety risk, which renders the process unfit for mass production. Herein, an isolated SWCNT dispersion displaying an LC behavior is prepared using sodium cholate without an acid treatment, and its phase transition behaviors are systematically investigated across the isotropic to biphasic to nematic phases. As the SWCNT concentration increases, the dispersion undergoes an isotropic-to-nematic phase transition in which the spindle-shaped LC droplets, or the so-called tactoids, and the Schlieren textures can be observed in the intermediate biphasic state and the nematic phase, respectively. The arrangements of SWCNTs in the tactoids and the Schlieren structures are directly investigated by polarized optical microscopy. The clear LC behaviors of the CNT dispersion suggest that the CNT orientations can be controlled by the normal surfactant-assisted method, which is a crucial advantage for the liquid-phase processing of CNT fibers and films.

Preserving the quality of carbon nanotubes (CNTs) is essential to fully utilize the characteristics in dispersions and other forms. To fabricate CNT dispersions retaining the quality, we propose to reduce CNT aggregate size distributions by viscous liquids at the initial stage from as-grown CNT powders originally possessing a wide aggregate size distribution. Higher viscosity solvents were found to highly disentangle the CNT powder and give a narrower CNT aggregate size distribution without impairing the quality. To show the advantages of these CNT dispersions, we demonstrated a 10 4 -fold increased electrical conductivity of CNT rubber composite based on the predispersion step of CNT powder in the rubber base compound with high viscosity. Our method can afford a high quality of CNT and avoid a long, heavy dispersion, which was conventionally carried out to decrease entangled, large size CNT aggregates, furthermore, applicable for fabrication of conducting polymer composites.

During melt processing, the moisture inside polylactide (PLA) easily induces hydrolysis, which deteriorates the mechanical and thermal properties of the product. The state of dryness of resin pellets must be monitored to prevent PLA hydrolysis. In this study, near-infrared (NIR) spectroscopy was applied to measure water content in PLA. In addition, the shape of the NIR spectrum is also affected by crystallization, which could lead to a reduction in the accuracy of evaluating the water content. The objective of this research is to construct a robust model for estimating the water content with varying dispersive extents of crystallization. Two methods for estimating water content measured during a drying process were conducted: the integration of absorbance and partial least squares (PLS) regression were conducted to estimate the water contents in PLA considering the effect of crystallization. The slope of the calibration line of the water content obtained from integrating absorbance varied between PLA with different crystallinities. This is due to the overlap between the NIR band of water and that of PLA crystal in the range of 5100-5400 cm. We found that the shape of the NIR spectrum was changed by crystallization, and the crystallinity, compared to the thickness of lamellae, was the dominant factor determining such a change of NIR spectra. The PLS model of water content constructed from only amorphous PLA showed large error of estimation in crystallized PLA. In contrast, the PLS model constructed from both amorphous and crystallized PLA estimated the water contents with lower errors. This was because latent variables obtained from both amorphous and crystallized PLA cancelled the effect of crystallization on NIR spectra.

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