Transient electric birefringence in suspensions of single-walled carbon nanotubes

In the torque created by an electric field, highly polarizable single-walled carbon nanotubes, suspended in dichloroethane, rotate and align with the field creating a transient induced birefringence (TEB). The magnitude of the birefringence, Δn, is followed in time by the switching of a square voltage pulse across the suspension and following the time evolution of the transmitted light through crossed polarizers. The variation of the magnitude of Δn with applied electric field and nanotube concentration is reported. We find that in spite of the polydisperse nature of the nanotube suspensions a single exponential growth is sufficient to describe the evolution of the birefringence, as the field is switched on. The low field reciprocal rise time of Δn varies as the square of the applied electric field, and the low field magnitude is proportional to the square of the applied electric field at low fields. These observations are discussed in the light of the classic Kerr effect. The TEB is shown to be dominated by induced dipole moments on the metallic nanotubes that form part of the suspension.