Water adsorption on M(111) (M = Pt, Cu, Ni, Ru(001)) surfaces and a new double layer structure of water at a Cu(111) electrode surface were investigated by surface X-ray diffraction, scanning tunneling microscopy and infrared reflection absorption spectroscopy methods. There exists a clear relationship between a double layer structure on an electrode under an electrochemical potential controle and a simulated electric double layer structure in UHV. Water molecules in an electric double layer exhibit an ordered and a disordered structure at negative and positive electrode potentials, respectively. Therefore, potential polarization (negative or positive electrode potential application) from an equilibrium potential operates the electrified interface to cause increased or decreased ordering, orientation and charge transfer of water molecules as well as water dissociation on the electrode surfaces. The origin of an immersed gap (the difference between the UHV and electrochemical situation) is attributed to charge transfer from water molecules to metal electrodes.
Physicochemical properties of thin film water on and between material surfaces have been reviewed. Infrared (IR) spectroscopy on thin film water sandwiched between various materials showed shifts of OH stretching vibration frequency maxima from 3400 cm−1 to about 3250 cm−1. These shifts vary with different materials, crystallographic orientations, film thickness (less than about 200 nm), dissolved ions and temperatures. The thin film water is supposed to have constrained structure close to ice and might have smaller diffusion coefficients and larger viscosity than the bulk liquid water. Standard molar volume, specific heat and entropy values for hydration water on some inorganic materials are different from these for the bulk liquid water and close to those for ice polymorphs. Sonic wave velocity measurements on a water-saturating rock suggest a larger P wave velocity for the thin film water than the value for bulk water. These structured thin water films with different properties from those of the bulk water can be present in the earth's interior and also in living materials such as cactus and human skin controlling dynamics of earth and life.
The interaction of H2O molecules with various oxide surfaces were investigated by using middle-infrared (MIR) and near-infrared (NIR) spectroscopies. The physicochemical properties of oxide surfaces such as hydrophilicity or hydrophobicity were then discussed from the viewpoint of the intermolecular hydrogen bonds in the H2O clusters. SiO2 surface showed hydrophobic property as compared to TiO2 or Al2O3 surfaces. However, smaller amount of H2O molecules on SiO2 surface can easily spread out to form H2O thin layer due to small contribution of intermolecular hydrogen bonds in the H2O clusters. As a result, such hydrophobic SiO2 surface shows high wettability. On the other hand, TiO2 or Al2O3 surfaces adsorbed large amounts of H2O and hydrocarbons because such polar molecules preferentially interact with such cationic (Ti4+ or Al3+) sites, showing both hydrophilic and oleophilic properties. However, larger amount of H2O molecules on the TiO2 or Al2O3 surfaces strongly interacted with each other to form aggregated bulky H2O clusters on the surfaces. As a result, such hydrophilic surfaces show low wettability.
We calculate physically insightful components of the rotational entropy of hydration of a solute using the angle-dependent integral equation theory combined with the multipolar model for water. It is shown that when a sufficiently large nonpolar solute is inserted into water, the rotational freedom (RF) of water molecules near the solute is significantly restricted due to the water structuring. When the solute has a moderate surface charge density (SCD), in the region next to the solute and in the region within which the solute-water surface separations are close to the molecular diameter of water, the RF of water molecules becomes higher than in the bulk. As the SCD increases, these regions shift slightly more outside with further enhancement of the RF, but the water molecules in contact with the solute turn largely restrained. It is shown that the appearance of water molecules with anomalously high RF is the most remarkable for a very large solute with high SCD like F-actin.
Characterization of the solid-liquid interfaces at the molecular level has recently become possible. This review summarizes our recent studies including new observations of liquid adsorption and a novel measurement for characterizing confined liquids. We have found that molecules with the hydrogen-bonding groups such as alcohol and acid form the molecular macroclusters when they are adsorbed on the silica surface in nonpolar solvents. This is caused by hydrogen-bonding between the surface silanol groups and adsorbed molecules as well as between these molecules. We also have developed a resonance shear measurement technique using the surface force apparatus which can control the thickness of the confined liquids at a resolution of 0.1 nm. These studies provide understandings of interfacial phenomena of the molecular level, which are not only important as foundations of interface science but useful for designing nano-and micro-devices and processes for manufacturing nano-materials.
In this article, we review our recent neutron diffraction and quasielastic scattering works on the following three water systems related to the formation of clathrate hydrates. The first is aqueous solutions of organic guest molecules. The second is the aqueous solutions prepared by applying high pressure of non-polar guest gas molecules. The third is the amorphous solids prepared by depositing mixed gases of water and guest molecules on a cold substrate (10 K). In the first system, the diffusion coefficient of water molecules was smaller than that in bulk water and it depended on the size of guest molecules. In the second system, the diffusion of water molecules became excessively slower below the formation temperature of gas hydrates and it depended on the amounts of solved guest molecules and formed hydrate crystals. In the third system, as the temperature of the amorphous solids increased, the local cage structure grew up above the glass transition temperature (ca. 130 K) and finally hydrate crystals formed at 165 K. All of the above results indicate that the local structural fluctuation of hydrate cage occurs in the liquid or amorphous states in advance of the crystallization of clathrate hydrates.
An atmospheric pressure plasma jet was used for the surface modification of fused silica glasses. The length of an atmospheric pressure argon plasma jet generated at an applied voltage of 10 kV, at a frequency of 9 kHz and at an argon gas flow rate of 10 L/min was approximately 3 cm. The wettability of the glass surface was improved by the irradiation of the argon plasma jet. The contact angle of a water drop on the glass surface after the argon plasma jet irradiation for 10 s decreased from 70 to 7 degree, indicated that the glass surface after the irradiation became super-hydrophilic. The super-hydrophilicity changed to ordinary hydrophilicity after one hour and the hydrophilicity was kept three weeks on the glass surface. From the results of XPS measurements, the super-hydrophilicity with irradiation was attributed to the removal of carbon atoms (organic compounds) adsorbed on the glass surface.