Flow and transport studies in (non)consolidated porous (bio)systems consisting of solid or porous beads by PFG NMR.

Displacement imaging pulsed field gradient nuclear magnetic resonance (PFG NMR) is applied to a number of porous model systems, consisting of either solid or porous particles. By pulsed field gradient nuclear magnetic resonance, the molecular displacement can be measured that occurs during a time interval, delta, between two consecutive magnetic field gradient pulses. In contrast to conventional techniques, which cover displacements over distances several times the bead diameter, pulsed field gradient nuclear magnetic resonance covers displacements in the order of subpore to several pore distances. Dimensionless scaling is possible based on the root-mean-square displacement normalised on the bead diameter. In solid particles, v and delta are interchangeable, although different flow regimens are covered. In porous particles, the exchange time between the stagnant mobile phase in the particles and the flowing outside must be taken into account with respect to delta as well as the porosity.

Quantitative measurement and imaging of transport processes in plants and porous media by 1H NMR.

NMR and MRI have been applied to transport processes, that is, net flow and diffusion/perfusion, of water in whole plants, cells, and porous materials. By choosing proper time windows and pulse sequences, magnetic resonance imaging can be made selective for each of the two transport processes. For porous media and plant cells the evolution of the spatial distribution of excited spins has been determined by q-space imaging, using a 20 MHz pulsed 1H NMR imager. The results of these experiments are explained by including spin-relaxation and exchange at boundaries. A 10 MHz portable 1H NMR spectrometer is described, particularly suitable to study the response of net flow in plants and canopies to changing external conditions.