SELF-DIFFUSION COEFFICIENT OF WATER CONFINED IN MESOPOROUS MCM-41 MATERIALS DETERMINED BY H-1 NUCLEAR-MAGNETIC-RESONANCE SPIN-ECHO MEASUREMENTS

H-1 Nuclear magnetic resonance (NMR) spin-echo measurements at 268 K h ave been performed on water-saturated mesoporous MCM-41 materials. The pores have cylindrical geometry with diameters in the range 18-40 Ang strom and length of approximately 1 mm. Using appropriate model calcul ations the self-diffusion coefficient (D) of water within the pore was estimated from the Carr-Purcell-Meiboom-Gill (CPMG) spin-echo envelop e curves. D was found to be in the range 0.17 . 10(-6) to 2.3 . 10(-6) cm(2)/s and could be expressed by an equation of the form D(-1)propor tional to D-infinity(-1) + alpha . l(c)(-2) where D-infinity is the se lf-diffusion coefficient of bulk water (l(c) = infinity) and alpha = ( 2.68 +/- 0.14). 10(-5) s. The low values for the diffusion coefficient s - compared to the diffusion coefficient of bulk water - are related to the strong interaction of the water molecules with the pore surface . Moreover, the spin-spin relaxation rate (1/T-2) was related to l(c) by application of the Bloembergen-Purcell-Pound (BPP) model.