Carbon nanotubes in suspension; Rotation & translation of mesoscopic cylinders in electric fields.

Research Group: 
Centre for Condensed Matter and Material Physics
Number of Students: 
Length of Study in Years: 
Full-time Project: 
QM Scholarship
Project Description: 
Single, double and multi-walled carbon nanotubes will, in suspension in an applied electric field, have a dipole moment induced along the tube axis. As a result the nanotube will rotate in the electric field to align it’s axis with the electric field. Through this alignment a suspension of nanotubes may pass from an optically isotropic fluid to a highly anisotropic fluid. This allows the dynamics of the alignment process to be followed using the consequent field induced optical changes of the suspension, in refractive index or absorption (Kerr Effect or Linear Dichroism) parallel and perpendicular to the applied electric field. The viscosity of the suspension may be found in this way and by observing the decay of the alignment (anisotropy) once the electric field is terminated the length distribution of the nanotubes may be discovered. The electric field may be applied in a variety of ways and the optical setup used to monitor the induced anisotropy can be varied allowing different aspects of the rotational dynamics to be observed. All of this is done using a uniform electric field. If a non-uniform electric field is used there will be a spatially differential force on the induced dipole causing translation of the nanotube. This force will also be differential with respect to nanotube type, metallic or semiconducting, long or short and may be employed to separate metallic from semiconducting nanotubes.
In this project the student will be involved in the use of electro-optics to find the polarisability of the nanotubes, the viscosity of the suspensions and the intrinsic viscosity of a collection of nano-cylinders. This will be done using a variety of suspending media with differing viscosities and dielectric constants. SWNTs, DWNTs, MWNTs and FeMWNTs will be studied and compared. Non-uniform electric fields, designed using different electrode configurations, will be used to attempt separation of metallic and semiconducting nanotubes which have very different polarisabilities and therefore induced dipole moments. A final goal would be to combine these two techniques designing an experiment that will use the induced electro-optic effect to monitor the semiconductor/metallic separation.

The student will gain experience in managing an experimental project from design through implementation to analysis of results and any re-design necessary in light of experience. The student will be using optics and electronics to perform measurements.

T.Lutz and K.J.Donovan, ”Macroscopic scale separation of metallic and semiconducting nanotubes by dielectrophoresis.” Carbon, 43, 12, 2508, 2005.
T.J.Robb-Smith, K.J.Donovan, K.Scott and M.Somerton, “Induced electro-optic effects in single walled carbon nanotubes. Part I: The electronic polarisability of metallic single walled carbon nanotubes.” Phys Rev B, 83,155414, 2011.
T.J.Robb-Smith, K.J.Donovan, K.Scott and M.Somerton, “Induced electro-optic effects in single walled carbon nanotubes. Part II: Hydrodynamics of carbon nanotubes in viscous media.” Phys Rev B, 83,155415, 2011.
K.J. Donovan and K. Scott, “Anomolous intrinsic viscosity of octadecylamine-functionalised carbon nanotubes in suspension.” J.Chem.Phys, 138, 244902, 2013.
A good BSc or MSci degree in Physics.
SPA Academics: 
Kevin Donovan