Vibrational Dynamics of Water within Mesoporous Materials at Different Hydration Levels during Adsorption and Desorption Processes

The vibrational dynamics of water within Vycor 7930 under different hydration levels and adsorption and desorption processes has been investigated by Raman measurements. Based on the successfully depressing the background fluorescence of Vycor, a new Gaussian peaking at 3590 cm−1 has been observed in the Raman spectrum of confined water. By comparison with the published Raman data of water within fully filled silica-based pores or reverse micelles, it is confirmed that a small confinement size may conceal the characteristic effect of hydrophilic interface. In addition, a density hysteresis observed within a filling fraction (ϕ) range of 0.25 < ϕ < 0.5 indicates that the cavitation model should be previously considered to explain the adsorption hysteresis of the water/Vycor system.