Effects of Surface Chemistry on Structure and Thermodynamics of Water Layers at Solid−Vapor Interfaces

Abstract

The effects of surface chemistry on the isotherm thickness and structure of the adsorbed water layer as well as the isosteric heat of adsorption and entropy of adsorption were studied using attenuated total reflection infrared spectroscopy. The degree of hydrophilicity seems to distinctively change the structure and thermodynamic properties of the water layers adsorbed on silicon oxide surfaces. On the highly hydrophilic silicon oxide surface covered with silanol groups, the water layer adsorbed at low humidities exhibits the OH stretching peak at 3230 cm -1 (characteristic of a solid-like water structure), and the isosteric heat of adsorption is much higher than the latent heat of ice sublimation. As the concentration of surface silanol groups decreases, both the initial isosteric heat of adsorption of water and the amount of solid-like water decrease. The water layer adsorbed on the hydrophilic surface at low humidities seems to have much lower entropies than bulk water, while the entropy of the water layer on the partially methylated surface is not much lower than that of bulk water. At high humidities, the liquid water structure becomes dominant in the adsorbed layer. The possible origins of high isosteric heat of adsorption and low entropy are discussed. † Part of the special section "Physical Chemistry of Environmental Interfaces".

Improved Substrate Protection and Self-Healing of Boundary Lubrication Film Consisting of Polydimethylsiloxane with Cationic Side Groups

“…The water uptake from the humid ambient is evident from the growth of the OH intensity. Note that the ratio of the O-H to C-H peak intensities observed for the CPL film is much lower than that observed for the octadecylsilane SAM on the SiO 2 surface [36]. This implies that the water repellency of the CPL film is superior than the octadecylsilane SAM in which the water molecules can reach the SiO 2 surface through defect sites [37].…”

“…This implies that the water repellency of the CPL film is superior than the octadecylsilane SAM in which the water molecules can reach the SiO 2 surface through defect sites [37]. The fact that the O-H peak position of H 2 O in the film is at *3,400 cm -1 implies that the water inside the film at RH [ 40% behaves more like a liquid [36,[38][39][40][41]. Therefore, the CPL film containing liquid-like water would exhibit a lower viscosity than the neat film without any water molecules.…”

Catalytic Role for Water in the Atmospheric Production of ClNO

“…8 Water on silica surfaces, including glass and quartz, is known to form a structured, "icelike" layer due to strong hydrogen-bonding interactions with surface-SiOH groups. 106 It is only at high relative humidity, approaching 80%, that sufficient water is adsorbed. At this point, water-water interactions become important and the spectroscopic signature starts to be indicative of that of bulk liquid water.…”

Electrochemical migration of Sn and Sn solder alloys: a review

“…On the other hand, the exact thickness of the moisture layer has never been unknown if the ECM test is performed using simulated environment tests such as the thermal humidity bias test where just the relative humidity and temperature are controlled. 28 Actually, there are several techniques such as ellipsometry, 96 sum-frequencygeneration vibrational spectroscopy and scanning polarization force microscopy, 97 attenuated total reection infrared spectroscopy 98 and ambient-pressure X-ray photoelectron spectroscopy 99,100 that can be used to in situ measure the thickness of ultra-thin electrolyte layer, even a few monolayers of water. Therefore, it can be expected that the exact thickness of electrolyte layer in the simulated environment tests of ECM can be known in the future.…”