Nanoscale infiltration behaviour and through-thickness permeability of carbon nanotube buckypapers

Carbon nanotube thin films or 'buckypapers' show potential for various applications including electrodes for energy devices, nanoscale filtration devices and composite materials. This paper reports on the study of through-thickness permeability of different buckypaper materials. The infiltration behaviours of different liquids into four types of buckypaper were investigated. Infiltration of the liquids into buckypaper was found to follow Darcy's law, except in the case of epoxy resin solution permeation into SWNT buckypaper. The results revealed that the permeability of SWNT buckypaper was of the order of 10(-19) m(2), which is about two orders of magnitude lower than the 10(-17) m(2) permeability for the MWNT buckypaper. The factors of wider pores, higher porosity and less surface area appear to contribute to a higher permeability, which is consistent with Darcy's law and the Kozeny-Carman model. The Kozeny constants of buckypapers correlated well with the tortuosity of their flow paths and nanoscale pore size. The polarity of working fluids did not show an impact on the permeability. Solutions with molecular size near the size of the nanopores in the buckypaper led to lower permeability due to the occurrence of pore blockage. In addition, a threshold pressure existed for liquid to infiltrate into nanoscale pores in buckypapers, which does not exist in fibre reinforcement preforms.