| The study of transport in nanoporous materials is very important from an industrial point of view. Examples of such materials include zeolites, carbon nanotubes and molecular sieves, and nano electromechanical systems. Diffusion and momentum transfer of fluids within these materials are far from fully understood, primarily due to the failure of continuum theories at such small length scales, and the apparent difficulty of current experimental techniques to probe transport at atomic length scales. In this work, we have developed novel molecular dynamics and coarse-grained statistical techniques to answer some of the pertinent fundamental issues in transport through such materials.; An exhaustive comparison of current molecular dynamics methods for studying transport diffusivity in nanoporous materials is presented first. A detailed coarse-grained analysis of a boundary-driven method has shown the existence of spurious mass and momentum transfer resistances within the simulation cell. Suggestions on eliminating these unwanted resistances are provided so as to improve the accuracy of the given method. The revised boundary-driven method is then employed to investigate the role of surface energy barriers at the pore exits on diffusion in zeolites. Diffusion of sluggish molecules is modeled using an activated transport theory. It is observed that the size of the pores, the loading and the temperature play a key role in determining the relative impact of the pore exit on diffusion within zeolites. We have also fundamentally investigated the phenomena of wall-slip in nanometer-sized channels at large Knudsen numbers. A novel scattering simulation method has been devised to compute and relate the degree of wall slip to the morphology of the wall. It is shown that momentum transfer at the surface can significantly affect the flow of sorbates within nanoporous materials, and that by tailoring the pore surfaces one can induce kinetic separation of gases. On a related front, an analytic theory to estimate the self-diffusivity of Knudsen gases through slit-pores is also developed. Scalings of transport rate with respect to pore width, temperature, inertia and surface roughness have been presented. In the end, we show that studying the transient decay of a momentum impulse yields estimates of the shear viscosity much more efficiently than through the use of conventional molecular dynamics approaches. |
