Diffusion enhancement in composites of nanotubes and porous structures

Abstract

Composites are often used to obtain enhanced material properties, including improved mechanical performance, enhanced conductivity, increased transport and other properties. Recent advances in carbon nanotube (CNT) composite porous materials suggest that CNTs may offer a greater advantage than conventional fillers, not only due to their extraordinary mechanical and electronic properties but also due to their smooth potential surface that allows for relatively high flux through the tubes. Using lattice Monte Carlo simulation, we study activated diffusion through various porous structures, and compare it with CNT composite materials. Flux enhancement is found to be substantial beyond the percolation threshold of nanotube aggregates, especially for relatively low-porosity structures. The simulation results are captured by a simple model that accounts for two contributions to the flux: diffusion within the percolating nanotube clusters and inside the porous substrate. Such porous structures may form better catalysts, membranes or molecular sieves where an increase in both surface area and flux is required.