Water behavior in hybrid silica gels as studied by 1H nuclear magnetic resonance relaxometry. Evidence of two hydration layers

Water behavior in silica gels involving hydrophobic sites that have been substituted to hydrophilic sites has been approached by 1H NMR relaxometry techniques. The latter method stems from the evolution of NMR longitudinal relaxation time T1 as a function of the Larmor frequency (the NMR measurement frequency). T1 measurements of the water protons have been carried out between 5 kHz and 10 MHz. This frequency range proved to be sufficient for detecting and characterizing two hydration layers although they exist in a very weak proportion (10−5–10−6). Self-diffusion coefficient of water in these two layers could be estimated. It turns out that only the first layer is influenced by hydrophobicity.

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► We applied NMR relaxometry techniques to the study of water in hybrid silica gels.
► NMR longitudinal relaxation time is studied as a function of the Larmor frequency.
► We found a very weak proportion of bound water (10−5–10−6) to silica matrix.
► The first hydration layer sensed hydrophobicity of MTMS precursors.
► The second hydration layer was not affected by hydrophobicity.