Aqueous dispersions of carbon nanotubes without passivation or functionalization

Carbon nanotubes (CNTs) form bundles due to their high surface energy, which difficult preparation of complex materials and devices. One way to overcome this problem is dispersing them in liquid media, separating individual entities from bundles and simplifying the storage, transportation and processing. Stable aqueous dispersions of nanotubes are very difficult to be obtained, and they are usually achieved using passivant agents or by inserting functional groups on the CNTs surface[1]. In this work we propose an innovative method based on literature[2] to prepare stable aqueous dispersions of single-walled and multi-walled carbon nanotubes that does not require passivant agents or surface functionalization. Solid carbon nanotubes were sonicated with commercial tetrahydrofuran, which contains a phenolic compound that generates electrical charges on materials. Organic dispersions of highly charged carbon nanotubes were added to deionized water, filtered, and purged with air to eliminate most of tetrahydrofuran, resulting in non-passivated and non-functionalized aqueous dispersions. These aqueous samples were also used to prepare thin films in liquid-liquid interfaces following a method proposed by our research group[3]. Aqueous dispersions presented zeta potentials between -20 and -30 mV and Raman spectroscopy performed in situ confirmed charge transference that is responsible for the surface electric potentials of nanotubes dispersions. Thin films were deposited over glass substrates up to three consecutive times because of the low concentration of aqueous samples, and presented sheet resistance of about 30 kΩ ⎕-1 and transmittance next to 80 % at 550 nm.