Hostname: page-component-586b7cd67f-g8jcs Total loading time: 0 Render date: 2024-11-29T09:39:22.024Z Has data issue: false hasContentIssue false

Probing Dynamics of water Molecules in Mesoscopic Disordered media by NMR Dispersion and 3D Simulations in Reconstructed Confined Geometries

Published online by Cambridge University Press:  21 March 2011

P. Levitz
Affiliation:
CRMD-CNRS, 1B rue de la ferollerie, 45071 Orléans Cedex 2, France
J.P. Korb
Affiliation:
LPMC-CNRS, Ecole Polytechnique, 91128 Palaiseau, France
A. Van Quynh
Affiliation:
Chemistry Department, University of Virginia, Charlottesville, VA 22901, USA
R.G. Bryant
Affiliation:
Chemistry Department, University of Virginia, Charlottesville, VA 22901, USA
Get access

Abstract

Disordered mesoporous materials with pore sizes ranging from 2 nm to some 10 nm develop large specific surface areas. These matrices can be easily filled with polar fluids And the interfacial region between the solid matrix and the pore network strongly influences the molecular dynamics of the entrapped fluid. A promising way to probe such a coupling on a large time-scale is to look at the dispersion of the nuclear spin-lattice relaxation rate of the polar liquid using field cycling NMR relaxometry technique. We have performed such an experiment on a fully hydrated porous Vycor glass, free of electron paramagnetic impurities. The proton nuclear magnetic relaxation rate (1/T1) exhibits a logarithmic dependence on Larmor frequency over the range from 0.01 to 30 MHz. A cross-over is observed below 0.1 MHz. In order to understand the relationship between geometric disorder, interfacial confinement, and nuclear magnetic relaxationdispersion (NMRD), we first compute an off-lattice reconstruction of the Vycor glass This model agrees with available experimental data (specific surface, porosity, chord length distributions, small angle scattering and tortuosity). A Brownian dynamics simulation is performed to analyze long time molecular self-diffusion and NMRD data. These later are well reproduced and appear to be connected with the translation diffusion of water near the SiO2 interface. The logarithmic character of the NMRD is specifically related to the interfacial geometry of the Vycor glass. Several other multiconnected interfacial structures such as periodic minimal surfaces do not exhibit such an evolution. Therefore, NMRD appears to be selectively sensitive to the interfacial geometry of mesoscopic disordered materials (MDM).

Type
Research Article
Copyright
Copyright © Materials Research Society 2001

Access options

Get access to the full version of this content by using one of the access options below. (Log in options will check for institutional or personal access. Content may require purchase if you do not have access.)

References

1. Bellisent-Funel, M.C., Chen, S.H., Zanotti, J.M., Phys. Rev. E.,51, 4558, (1995).Google Scholar
2. Callaghan, P.T., Coy, A., MacGowan, D., Packer, K.J., Zelaya, F.O.. Nature, 351,467, (1991).Google Scholar
3. Noack, S., Progress in NMR Spectroscopy, 18,171276,(1986).Google Scholar
4. Staps, S., Kimmich, R., Niess, J., J. Appl. Phys., 75, 529, (1994).Google Scholar
5. Korb, J.P., Whaley-Hodges, M., Bryant, R.G., Phys. Rev. E., 56, 1934,(1997).Google Scholar
6. Levitz, P., Ehret, G., Sinha, S.K., Drake, J.M.. J.Chem. Phys., 95, 6151, (1991).Google Scholar
7. Kimmich, R., Weber, H.W.. Phys. Rev. B, 47,11788,(1993).Google Scholar
8. Levitz, P., Advances in Colloid and Interface Science, 76–77, 71106, (1998).Google Scholar
9. Berk, N. F., Phys. Rev. A., 44, 5069, (1991).Google Scholar
10. Halle, B., Wennerstrom, H., J. Chem. Phys., 75, 1928 (1981).Google Scholar
11. MacKey, A.L., Proc. R. Soc. London, Ser A, 47, 442 (1993).Google Scholar
12. Halle, B., Ljunggren, S., Lidin, S., J. Chem. Phys., 97, 1401 (1992).Google Scholar