Layer-by-Layer Electrostatic Self-Assembly of Single-Wall Carbon\nNanotube Polyelectrolytes

Abstract

We have used anionic and cationic single-wall carbon nanotube polyelectrolytes (SWNT-PEs), prepared by the\nnoncovalent adsorption of ionic naphthalene or pyrene derivatives on nanotube sidewalls, for the layer-by-layer\nself-assembly to prepare multilayers from carbon nanotubes with polycations, such as poly(diallyldimethylammonium)\nor poly(allylamine hydrochloride) (PDADMA or PAH, respectively), and polyanions (poly(styrenesulfonate), PSS).\nThis is a general and powerful technique for the fabrication of thin carbon nanotube films of arbitrary composition\nand architecture and allows also an easy preparation of all-SWNT (SWNT/SWNT) multilayers. The multilayers were\ncharacterized with vis−near-IR spectroscopy, X-ray photoelectron spectroscopy (XPS), surface plasmon resonance\n(SPR) measurements, atomic force microscopy (AFM), and imaging ellipsometry. The charge compensation in multilayers\nis mainly intrinsic, which shows the electrostatic nature of the self-assembly process. The multilayer growth is linear\nafter the initial layers, and in SWNT/polyelectrolyte films it can be greatly accelerated by increasing the ionic strength\nin the SWNT solution. However, SWNT/SWNT multilayers are much more inert to the effect of added electrolyte.\nIn SWNT/SWNT multilayers, the adsorption results in the deposition of 1−3 theoretical nanotube monolayers per\nadsorbed layer, whereas the nominal SWNT layer thickness is 2−3 times higher in SWNT/polyelectrolyte films\nprepared with added electrolyte. AFM images show that the multilayers contain a random network of nanotube bundles\nlying on the surface. Flexible polyelectrolytes (e.g., PDADMA, PSS) probably surround the nanotubes and bind them\ntogether. On macroscopic scale, the surface roughness of the multilayers depends on the components and increases\nwith the film thickness.