Characterization of the electric double layers of multi-walled carbon nanotubes, laponite and nanotube + laponite hybrids in aqueous suspensions

To characterize the electric double layers (EDLs) of multi-walled carbon nanotubes (NTs), laponite clay disks and NT + laponite hybrid particles, their electrophoretic mobility was investigated as a function of pH and concentration of electrolytes (KCl, CaCl2 and AlCl3). The electrokinetic behaviour of NTs resembles that of the lyophobic colloids. An increase in pH from 2 to 12 resulted in substantial increase of the absolute (negative) values of the electrophoretic mobility of NTs due to dissociation of surface hydroxyl and carbonyl groups, which was identified by infra-red (IR) spectroscopy. The observed attraction between similarly charged colloidal particles of NTs and laponite was explained by the highly heterogeneous distribution of negatively charged functional groups on the surface of NTs and difference in electrophoretic mobility of NT and laponite particles.