Redox modulation of electroosmotic flow in a carbon nanotube membrane

Electroosmotic flow (EOF) is widely used to manipulate solutions in capillaries and microfluidic devices, and more recently in the nanotubes of a carbon nanotube membrane. In all of these applications it is important to control both the rate and direction of EOF through the system, independently of the electric field that drives EOF. For this reason, there has been considerable recent effort devoted to developing ways of modulating the rate and direction of EOF. We describe here a new method, and we use the carbon nanotube membrane (CNM) system to demonstrate this method. This new method entails coating the inside walls of the carbon nanotubes within the CNM with redox-active polymer films. The redox polymer, poly(vinylferrocene), can be reversibly electrochemically switched between an electrical neutral and a polycationic form. This provides a way for controlling both the magnitude and the sign of the surface charge on the nanotube walls, which in turn allows for control of both the rate and direction of EOF through the CNM.