Anomalous effective hydrodynamic radius of octadecylamine functionalised single walled carbon nanotubes

In a uniform electric field, single walled carbon nanotubes (SWCNTs) in suspension become electrically polarised and are caused to rotate due to the resulting torque acting on the induced dipole moment. This rotation is followed in real time as an induced optical anisotropy, linear dichroism, which is produced as a result. These observations allow the polarisability of the nanotubes and the effective viscosity of the suspending medium to be determined. These techniques are used here to determine the effective radius of an octadecylamine (ODA)-functionalised SWCNT and its polarisability and to compare these values with those found for non-functionalised SWCNTs. The effective radius is found to be a factor 25 times larger than that of a non-functionalised SWCNT and far in excess of the value expected on steric grounds alone. Alternatively the local viscosity seen by the functionalised SWCNTs is 2.2 times greater than the macroscopic viscosity of the dichloroethane in which they are suspended. The polarisability of the metallic SWCNTs is substantially unchanged as a result of the functionalisation.