Analytical Sciences

Temperature and Size Effects on Structural and Dynamical Properties of Water Confined in 1 – 10 nm-scale Pores Using Proton NMR Spectroscopy

Yuta FUKATSU, Kyojiro MORIKAWA, Yasuhisa IKEDA, and Takehiko TSUKAHARA

Laboratory for Advanced Nuclear Energy, Tokyo Institute of Technology, 2-12-1-N1-6 Ookayama, Meguro, Tokyo 152-8550, Japan

We were able to fill 1 – 10 nm-scale silica pores with water by vapor condensation, and examined the freezing phenomena, structures, and molecular motions of the confined water in the temperature range from 293 to 188 K by ¹H-NMR spectroscopy. The results showed that almost all water molecules confined in 10 nm-scale pores were frozen and that approximately half of the water confined in 1 nm-scale pores existed in the liquid state even below the freezing point. The water adsorbed on the pore surfaces was estimated as a monolayer in 2.58 nm pores and bi- and tri-layers in 6.48 nm and larger pores, respectively. Furthermore, it was clarified from the proton relaxation rate (¹H-1/T₁) measurements that the molecular motions of adsorbed water itself were restricted by nanoconfinement and were extremely dependent on the conditions of proton exchange and hydrogen bond rearrangements of the adsorbed water.

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