Time dependent diffusion studies in partially filled porous glasses using the MAGROFI technique

1. Introduction The most popular principle of diffusion measurements by NMR is the attenuation of spin echoes due to incomplete refocusing of coherences as a consequence of incoherent molecular displacements in the diffusion interval of the pulse sequence [0-Fehler! Verweisquelle konnte nicht gefunden werden.]. Attenuation of echoes on these grounds arises in the presence of pulsed or steady gradients of the main magnetic flux density BB 0 or alternatively of the radio frequency flux density B 1 B [Fehler! Verweisquelle konnte nicht gefunden werden.]. Moreover, BB 1 and B 0 B gradients can be applied in mixed form. If suitably matched such mixed combinations of gradients lead to " nutation echoes " [Fehler! Verweisquelle konnte nicht gefunden werden.] the diffusive attenuation of which can also be used for molecular displacement studies. Moreover, implementing nutation echoes it is possible to accomplish diffusion measurements with chemical shift resolution in inhomogeneous static magnetic fields [0]. With the techniques mentioned above, a non-equilibrium magnetization distribution is first prepared in the form of a " helix " or as magnetization " grid ". Translational diffusion tends then to level the magnetization distribution during the diffusion time. The leveling process is monitored via spin echo attenuation. An alternative method is to directly image the magnetization profile across the sample. A technique for rendering the magnetization profile is the magnetization grid rotating-frame imaging (MAGROFI) pulse sequence [0]. The appealing advantage of the MAGROFI technique in comparison with the rotating frame techniques based on rotary or nutation echoes is that no constant B