화학공학소재연구정보센터
Journal of Physical Chemistry B, Vol.101, No.50, 10880-10886, 1997
Water on Salt - An Infrared Study of Adsorbed H2O on NaCl(100) Under Ambient Conditions
Using infrared spectroscopy, we were able to determine that water, under ambient conditions, adsorbs onto the surface of NaCl(100) into a liquidlike thin film. Photometric methods allowed coverages to be monitored from near Theta = 0.1 (0.1 monolayer) to Theta = 3. The shifting band center of the -OH stretching region suggests changing hydrogen-bonding environments with coverage. In the submonolayer region, water-surface bonds are favored over water-water hydrogen bonds. Thin film coverages near Theta = 2 produce spectra essentially indistinguishable from that of a saturated salt solution suggesting a liquidlike hydrogen-bonded network. This thin Rim can be reversibly removed from the NaCl(100) surface. However, at coverages near Theta = 3, dissolution begins and the salt surface becomes visibly damaged. Isothenns measured at 12 and 24 degrees C allowed the determination of the isosteric heat of adsorption. This heat of adsorption for coverages near Theta = 2 is close to that of the heat of condensation of liquid water, again suggesting that the thin film is liquidlike. A model for thin film water growth on NaCl(100) under ambient and cryogenic conditions is proposed.