Structural studies of water in hydrophilic and hydrophobic mesoporous silicas: An x-ray and neutron diffraction study at 297 K

J. Jelassi, T. Grósz, I. Bakó, M. C. Bellissent-Funel, J. C. Dore, H. L. Castricum, R. Sridi-Dorbez

Research output: Contribution to journalArticle

27 Citations (Scopus)

Abstract

Water confined in a sol-gel network has been characterized by x-ray and neutron diffraction for two samples of mesoporous silica: one with a hydrophilic character (a nonmodified one) and another with a hydrophobic character (a modified one with a methylated internal pore surface). The pore size has been previously characterized J.Jelassi, Phys. Chem. Chem. Phys. 134, 1039 (2010) to have a mean pore diameter of approximately 55 Å. The diffraction measurements presented in this paper have been made at room temperature 293 K for a filling factor of 0.45, giving a mean thickness of 8-9 Å for the water layer. The results show that the local order of the confined water molecules in the intermediate region of 3-6 Å is significantly different from that of the bulk water and also for the two different environments. For the hydrophilic sample, the siloxyl groups at the surface modify the water structure through the effects of interfacial hydrogen-bonding, which influences the orientational configuration of local water molecules and creates a modified spatial arrangement in the pore. In the case of the hydrophobic sample, there is no specific interaction with the pore wall, which is primarily van der Waals type, and the water molecules at the interface are differently oriented to create a hydrogen-bonded network linked more directly to the rest of the water volume. In the present circumstances, the thickness of the water layer has a relatively small dimension so that the interpretation of the measured diffraction pattern is not as straightforward as for the bulk liquids, and it is necessary to consider the effects of diffraction-broadening from a distributed sample volume and also the contribution from cross-terms that remain after conducting a wet-minus-dry analysis procedure. These analytic difficulties are discussed in the context of the present measurements and compared with the work of other groups engaged in the study of water confined in different environments. The present results, again, emphasize the complexity influencing the properties of water in a confined geometry and the strong influence of surface interactions on its behavior.

Original languageEnglish
Article number064509
JournalThe Journal of Chemical Physics
Volume134
Issue number6
DOIs
Publication statusPublished - Feb 14 2011

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Neutron Diffraction
Neutron diffraction
Silicon Dioxide
neutron diffraction
x ray diffraction
X-Rays
silicon dioxide
X rays
Water
water
porosity
Molecules
Diffraction
molecules
Polymethyl Methacrylate
hydrogen
Hydrogen Bonding
diffraction
Diffraction patterns
surface reactions

ASJC Scopus subject areas

  • Physics and Astronomy(all)
  • Physical and Theoretical Chemistry
  • Medicine(all)

Cite this

Structural studies of water in hydrophilic and hydrophobic mesoporous silicas : An x-ray and neutron diffraction study at 297 K. / Jelassi, J.; Grósz, T.; Bakó, I.; Bellissent-Funel, M. C.; Dore, J. C.; Castricum, H. L.; Sridi-Dorbez, R.

In: The Journal of Chemical Physics, Vol. 134, No. 6, 064509, 14.02.2011.

Research output: Contribution to journalArticle

Jelassi, J. ; Grósz, T. ; Bakó, I. ; Bellissent-Funel, M. C. ; Dore, J. C. ; Castricum, H. L. ; Sridi-Dorbez, R. / Structural studies of water in hydrophilic and hydrophobic mesoporous silicas : An x-ray and neutron diffraction study at 297 K. In: The Journal of Chemical Physics. 2011 ; Vol. 134, No. 6.
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