Delivered by Publishing Technology to: Guest User IP: 119.106.13.154 On: Tue, 02 Jun 2015 14:50:16 Copyright: American Scientific Publishers Materials Express Article Copyright © 2013 by American Scientific Publishers All rights reserved. Printed in the United States of America 2158-5849/2013/3/037/006 doi:10.1166/mex.2013.1096 www.aspbs.com/mex Depolarized dynamic light scattering study of multi-walled carbon nanotubes in solution Takeshi Eitoku 1 , Masayoshi Tange 1 , Haruhisa Kato 2 , and Toshiya Okazaki 1, * 1 Nanotube Research Center, National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba 305-8565, Japan 2 National Metrology Institute of Japan, National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba, Ibaraki 305-8565, Japan ABSTRACT Evaluation of size and morphology of carbon nanotubes in solution has been one of the key issues for their applications. Here we investigate the dispersion states of several multi-walled carbon nanotubes (MWCNTs) in aqueous solutions by the depolarized dynamic light scattering (DDLS) technique. The estimated size and mor- phology by monitoring the rotational diffusion and the translational diffusion are compared with those obtained by transmission electron microscope (TEM) image analysis. Agreement between the DDLS and TEM results suggest that DDLS is a quite powerful tool for evaluating the morphology of MWCNTs in solutions. Keywords: Carbon Nanotubes, Dispersion, Depolarized Dynamic Light Scattering, Raman Scattering, Transmission Electron Microcopy. 1. INTRODUCTION Because of their superior mechanical, optical, thermal and electrical properties, carbon nanotubes (CNTs) have been paid particular attention since their discovery. 1 2 Although much progress has been made so far, it is widely recognized that the bottleneck for applications is to pre- pare the homogeneous dispersion of CNTs. Indeed the functionality of a wide range of applications depends on the individual CNTs rather than the CNT bundles. For example, addition of small amount of CNTs can change electrically insulating polymer to a conductive composite, which is not possible with the same amounts of conductive fillers such as carbon black. 3 This can be explained by the reduction of percolation threshold due to the extremely high aspect ratio of CNTs. 4 5 The dispersion state and the morphology in solution should also affects the toxicity of CNTs 6 7 Practically, tube diameter and agglomeration ∗ Author to whom correspondence should be addressed. Email: toshi.okazaki@aist.go.jp states are significant for cellular response. 6 8 The evalua- tion of dispersion states of CNTs in solutions has therefore been one of the serious issues in the CNT community. Currently, direct-imaging techniques such as trans- mission electron microscopy (TEM), scanning electron microscopy (SEM), and atomic force microscopy (AFM) are most commonly used to characterize the average dimensions of CNTs. 2 However, these methods often suffer from the conditions of samples. Because samples should be dried and fixed on a substrate or grid, the obtained results do not necessarily reflect the in situ morphology and state of CNTs in solution. Moreover, microscopy methods require significant time for charac- terization and analysis. For these reasons, the establish- ment of bulk evaluation protocol in solution phase by rapid and convenient techniques is strongly required. Recently, depolarized dynamic light scattering (DDLS) was used for characterizing the morphology of CNTs in solution. 9–11 Since the technique independently provides the rotational (D r  and translational (D t  diffusion coefficients of the dispersed particles, the shape and the size of the particles Mater. Express, Vol. 3, No. 1, 2013 37