Individually isolated single wall carbon nanotubes with controlled surface charge density

Individually isolated single wall carbon nanotubes (SWNTs) with controlled surface charge density in water have been developed. First, the polymerizable cationic surfactant, cetyltrimethylammonium 4-vinylbenzoate (CTVB), is self-assembled on the hydrophobic surface of SWNTs in the presence of different amount of polymerizable co-monomer, sodium 4-styrenesulfonate (NaSS). Second, the self-assembled CTVB/NaSS monolayer is permanently fixed by in situ polymerization, making individually isolated SWNT dispersion in water. The surface charge density of functionalized SWNTs is controlled by the amount of NaSS relative to that of CTVB. The zeta potential of the functionalized SWNTs is systematically varied from positive to negative (+12.3 ∼ −47.8 mV) as the concentration of NaSS is increased from 0 to 60 mol % relative to the CTVB concentration. The charge variation is understood in terms of an overcharging effect in the charged colloidal system. The small angle neutron scattering (SANS) measurements show that electrostatic interaction between the functionalized SWNTs is strongly dependent on the NaSS concentration, which is consistent with the zeta potential measurements. The SANS measurements also show that the thickness of polymerized CTVB/NaSS monolayer adsorbed on SWNTs is almost constant at 1.89 nm regardless of the NaSS concentration, and the microstructure and surface charge are well maintained at high temperature (60 °C) as well as even after harsh condition such as freeze-drying.