Electrokinetic potential of multilayer carbon nanotubes in aqueous solutions of electrolytes and surfactants

The effect of electrolytes with single-, double- and triple-charged counterions, as well as cationic (cetyltrimethylammonium bromide) and anionic (sodium dodecyl sulfate) surfactants, on the electrokinetic potential of multiwall carbon nanotubes prepared via catalytic pyrolysis of propylene in a gas phase according to the CCVD technology has been studied. It has been shown that the influence of different electrolytes on the electrophoretic mobility of the nanotubes does not differ essentially from their effect on the behavior of well-studied inorganic dispersed particles; i.e., the dependence of the absolute values of the ζ-potential on the concentration of a 1: 1 electrolyte passes through a maximum and the introduction of double-charged counterions dramatically reduces the ζ-potential, while the addition of triple-charged cations and a cationic surfactant causes charge reversal of the nanotube surface. The adsorption of sodium dodecyl sulfate in a neutral medium increases the negative ζ values; this effect evens out in the presence of an alkali due to a rise in the electrostatic repulsion between surfactant anions and nanotube surface, which bears a high negative charge resulting from the dissociation of surface functional groups.