Anomalous surface diffusion of water compared to aprotic liquids in nanopores

Abstract

1H nuclear magnetic relaxation dispersion experiments show remarkable differences between water and acetone in contact with microporous glass surfaces containing trace paramagnetic impurities. Analyzed with surface relaxation theory on a model porous system, the data obtained for water show that proton surface diffusion limited by chemical exchange with the bulk phase permits long-range effectively one-dimensional exploration along the pores. This magnetic-field dependence coupled with the anomalous temperature dependence of the relaxation rates permits a direct interpretation in terms of the proton translational diffusion coefficient at the surface of the pores. A universal rescaling applied to these data collected for different pore sizes and on a large variety of frequencies and temperatures, supports this interpretation. The analysis demonstrates that acetone diffuses more slowly, which increases the apparent confinement and results in a two-dimensional model for the molecular dynamics close to surface relaxation sinks. Surface-enhanced water proton diffusion, however, permits the proton to explore a greater spatial extent of the pore, which results in an apparent one-dimensional model for the diffusive motions of the water that dominate nuclear spin relaxation.

Low-field NMR water proton longitudinal relaxation in ultrahighly diluted aqueous solutions of silica-lactose prepared in glass material for pharmaceutical use

“…However, when bound on the surface of glass, like through adsorption, paramagnetic ions could enhance the longitudinal relaxation [14]. A lowfield (0.01-3 MHz) tH NMRD was described in water and aprotic liquids in contact with microporous gtass beads containing trace paramagnetic impurities and interpreted in terms of confinement which enhances reencounter between protons and paramagnetic centers [ 15,16].…”

“…The NMR relaxation of water IH, 2H or 170 magnetic nuclei in heterogeneous media, among which silica glass particles, has been widely studied [14][15][16][17][18][19][20][21][22]. In particular, a low-field water proton NMR dispersion was described in silica particle suspensions, interpreted in terms of restricted water motion, cross-relaxation of chemical exchange between the protons of the surface silanols (Si-OH) and those of water [17][18][19].…”

An NMR Investigation of Water Self-Diffusion and Relaxation Rates in Controlled Ionic Strength Laponite Sols and Gels

“…At solid-liquid interfaces, diffusion is slower than in the bulk liquid phase. This has been observed in a variety of interfacial systems, including porous solids, proteins, and polymer solutions (2)(3)(4)(5). Finally, a third mobility mechanism, restricted to the sol state, is Brownian motion of the particles themselves, carrying with them their adsorbed layers.…”

Structure et dynamique d'une couche de liquide au voisinage d'une surface solide de milieux nanoporeux

“…Nous venons de terminer une étude de relaxation du proton de l'eau en champs « cyclés » dans des billes de verres poreuses calibrées qui présentent une faible fraction d'impuretés paramagnétiques à la surface des pores [21]. Les contributions de surface des courbes de dispersion que nous avons obtenues pour différentes tailles de pores et différentes tempé-ratures suivent une loi universelle 1/T 1 µ 1/(w I t sd ) 1/2 ( fig.…”