The Conformation of Polymers Dispersing Single-Walled Carbon Nanotubes in Water.

Amphiphilic polymers have been used to disperse single-walled carbon nanotubes (SWCNT) in water. The polymer conformation around the nanotube surface is important for understanding the nature of the interactions leading to successful dispersions. Two extreme cases are ``tight wrapping'' of the polymer around the nanotube and ``loose adsorption'' of solvated polymer coils on the nanotube surface. We studied aqueous dispersions of SWCNTs with an alternating copolymer of styrene and sodium maleate (PSSty) by small-angle neutron scattering (SANS) and cryo transmission electrons microscopy (cryo-TEM). Dispersion of long, isolated nanotubes and thin bundles was revealed by cryo-TEM. The SANS patterns (at different solvent contrasts) were evaluated by a modification of Pedersen's ``cylindrical block copolymer micelle'' model, depicting the nanotube-polymer complex as composed of a thin core, the radius of which is about 20 A thus containing about 3-4 nanotubes, surrounded by a thick corona of water-swollen polymer coils with a radius of gyration of 150-170 A. Long-term stabilization is achieved by the steric barrier provided by the adsorbed polymer coils reinforced by electrostatic repulsion due to charged groups distributed along the polymer.