Layer-by-layer assembly of multiwall carbon nanotubes on spherical colloids

Multiwall carbon nanotubes (CNTs) have been assembled on various types of colloidal templates using the well-known polyelectrolyte-assisted layer-by-layer (LBL) assembly technique. Dense mono- and multilayers of CNTs were successfully deposited on silica, polystyrene, and melamine spherical colloids of different size, showing that relatively short CNTs completely wrap the surface of the spheres, while long nanotubes stick out of the surface, allowing them to contact various spheres at the same time. Decomposition of the colloidal template leads to formation of hollow CNT spheres, which was demonstrated through treatment of melamine@CNT particles with HCl. The deposition was also carried out on ordered arrays of polystyrene particles, leading to nanostructured, conducting CNT assemblies. Rupture of the assemblies with ultrasound shows that the assembly only takes place on one-half of the colloid spheres, so that "Janus" particles with asymmetric functionalities can be easily prepared.