Nanofluidics in tailored carbon nanotube membranes

Carbon nanotubes and carbon membranes are two rapidly growing areas of research. At the interface of these two areas are carbon nanotube membranes (CNM), an invention which is analogous to gold nanotube membranes but which has just recently begun attracting heavy interest. CNMs are prepared by template synthesis using nanoporous alumina templates which are commercially available and are grown in the lab as well. CNMs are an interesting and useful platform for the study of electroosmotic flow (EOF). In particular, the structural, physical, and chemical properties of nanotubes can be tailored using both the template method and electrochemical modification to exhibit nanofluidic control.; Template synthesis of CNMs entails chemical vapor deposition (CVD) of carbon into alumina membranes. The inherent flexibility of the method enables the CNM structural characteristics to be tailored to maximize permeability while maintaining good permselectivity. CNMs were prepared with pore diameters ranging from 10 to 200 nm and having either symmetric or asymmetric pore structures. Highly-ordered membranes were prepared in which the nanotubes are near-perfect cylinders and extremely monodisperse in morphology.; EOF across template-prepared CNMs was used to modulate molecular transport. EOF in the direction of diffusion enhances transport across the membrane. However, EOF in the opposite direction diminishes, even eliminates, transport. In addition, the chemical and physicochemical properties of CNMs were tailored in order to control EOF by manipulating the experimental conditions. EOF was controlled and switched by adjustment of electrolyte concentration and pH as well as with the addition of small concentrations of surfactant.; The electrochemical capabilities of carbon nanotubes have also been used to tailor the properties of CNMs. Electromodified CNMs with a carboxylic functionality enhanced EOF while membranes with an amino functionality reversed it. Poly(phenylene oxide) nanotubes were grown inside carbon nanotubes by electropolymerization. EOF was passivated in these membranes even while diffusion and electrophoresis were still operative. A new approach for modulating EOF based on redox control of surface charge in poly(vinylferrocene) modified CNMs was demonstrated. The advantage of this method over other analogous electric-field methods is that it could be implemented with only a small battery for surface charge-control.