Dispersion of carbon nanotubes in ethanol by a bead milling process

Carbon nanotubes (CNTs) were dispersed in ethanol by bead milling to form a CNT suspension. The size and shape of the CNTs were not changed after bead milling. The Brownian motion of the CNTs was observed by an optical microscope. It was shown by analysis off the trajectory of individual CNTs that the diffusion coefficient of their translational Brownian motion was 4.5 x 10(-13) m(2) s(-1). The ratio of the particle mobilities due to drift flow and diffusion flow was 2.4, which is almost the same as for a high-molecular-weight protein. Shear thinning occurred in the CNT suspension, which means that the CNTs were oriented in the suspension under a high shear rate at low viscosity. The intrinsic viscosity for shear rates of 0 and infinity agreed with those calculated using Simha's equation and Leal and Hinch's equation, respectively. Based on the experimental results, the CNTs were found to be well dispersed as isolated and nanosized rod-like particles in the suspension. CNT-dispersed Si3N4 ceramics were fabricated using the CNT suspensions. As a result, the bead milling improved the bend strength of the CNT Si3N4 ceramics compared with the wet ball milling because granules of CNTs were eliminated by the bead milling. (C) 2011 Elsevier Ltd. All rights reserved.