Monitoring the dispersion process of SWNTs in aqueous solutions by UV-vis and Raman spectroscopies

The current bottleneck to carbon nanotubes (CNT) application in composite materials field consists in the difficulty of dispersing them in solvents. As a result of strong van der Waals interactions, as produced CNTs are tightly bundled in ropes of several tubes, rendering the carbon-powder insoluble in aqueous and organic liquids and thus unprocessable. The interest in applications that require water-soluble CNTs is growing and much attention is being directed to the study of surfactant aqueous solutions. In a typical dispersion procedure, after the surfactant has been adsorbed on the nanotube surface by hydrophobic or pi-pi interactions, ultrasonication helps nanotubes debundling, providing a mechanical energy able to overcome van der Waals interactions in CNT bundles. The electrostatic repulsion between surfactant polar heads that remain in solution allows the colloidal stability. In this work the dispersibility of HiPCO Single Walled Carbon Nanotubes (SWNT) in different surfactant solutions has been evaluated by using UV-vis and Raman spectroscopies. UV absorbance as well as intensity of SWNTs characteristic Raman bands have been studied as a function of sonication time for each type of surfactant. Moreover the surface morphology of SWNTs films obtained by solutions drying has been observed by using Scanning Electron and Atomic Force Microscopies.