(604a) Aligned Carbon Nanotube Membranes with Enhance Fluid Flow and Active Gate Keeper Control

Carbon nanotubes have three key attributes that make them of great interest for novel membrane applications 1) atomically flat graphite surface allows for ideal fluid slip boundary conditions 2) the cutting process to open CNTs inherently places functional chemistry at CNT core entrance and 3) CNT are electrically conductive allowing for electrochemical reactions and application of electric fields gradients at CNT tips. To explore the hypothesis of ?Gatekeeper' membrane selectivity, the entrances to CNT's cores were functionalized with aliphatic amines of different lengths, charged dye molecule and poly-peptides. A hindered diffusion model with a geometry of CNT tip functionalization, not along the length of CNT core, was consistent with the experimentally observed selectivities. Bio-chemical gating of CNTs is also seen by tethering desthiobiotin to CNT tips with the reversible binding to streptavidin. The complete ATP cycle (phosphylation/dephosphylation) can be performed on CNT tips with corresponding modulation of flux across CNT membrane. The functional density of tethered charge molecules can be substantially increased by the use of electrochemical grafting of diazonium salts. Voltage modulated membranes were realized with tethered molecules at the tips of CNTs being drawn into the CNT core at positive bias thus hindering/gating flux across the membrane. In general, the transport mechanisms through CNT membrane are a) ionic diffusion is near bulk expectation with no enhancement from CNT b) gas flow is enhanced by ~1-2 order of magnitude due to specular reflection off of flat graphitic surface c) and pressure driven flux of a variety of solvents (H2O, hexane, decane ethanol, methanol) are 4-5 ORDERS OF MAGNITUDE FASTER than conventional Newtonian flow due to atomically flat graphite planes inducing nearly ideal slip conditions.