MRI of mass transport in porous media: Drying and sorption processes

A study was conducted to demonstrate drying and sorption processes involved in performing magnetic resonance imaging (MRI) of mass transport in porous media. It was demonstrated that MRI of fluids in porous materials encountered a number of extra problems and difficulties in comparison with objects containing bulk liquids and to soft tissue of a living organism. The pores were too small for MRI to provide direct access to the processes on the length scale of individual pores. Each pixel of an image normally corresponded to a number of pores, with the measured NMR signal essentially averaged over each voxel. It was also demonstrated that the interactions of the fluid molecules with the pore walls significantly reduced their nuclear spin relaxation times for samples with a very large specific surface area and for materials containing paramagnetic impurities in liquids and some gases.