Preparative Ultracentrifuge Method for Characterization of Carbon Nanotube Dispersions

Quantitative characterization of carbon nanotube (CNT) dispersions is critical for developing various CNT-based applications, e.g., transparent conducting thin films, CNT thin film transistors, CNT-reinforced composites, etc. Using both of the preparative ultracentrifuge and absorption spectrum measurements, this paper presents a simple, easy-to-use, and reproducible method to experimentally determine the sedimentation function of carbon nanotube dispersions. This information can then be used for the semiquantitative characterization of the dispersion of CNT in various liquid media. Theoretical analysis of the sedimentation function based upon the conventional ultracentrifugation model allows for the determination of the apparent sedimentation and diffusion coefficients for a specific SWNT dispersion. As demonstrated in the examples, this method, along with dynamic light scattering, was used for studying the processing-structure relationship of SWNT/H2O dispersions. In brief: (1) size reduction of SWNT bundles due to exfoliation (diameter reduction) and shortening/cutting (length reduction) occurs simultaneously during the sonication process; power-law dependence of the diameter and length reduction on the sonication duration were observed; (2) size reduction of SWNT bundles reflected by the sedimentation function strongly depends upon the amount of dispersion being processed; for the same sonication conditions, the greater the amount of the dispersion, the less efficient the exfoliation of the SWNT bundles is; (3) under the same sonication conditions, the sedimentation coefficient of sodium dodecylbenzenesulfonate (SDBS) assisted SWNT/H2O is significantly smaller than that of Triton X-100, which indicates the superior dispersing capability of the former surfactant.