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The effects of a solvent on the surface modification progress of fumed silica were investigated. Hexane, toluene, and acetone as the reacting solvent and hexyltriethoxysilane as the surface modifier were used. After a 1 h reaction at 50 °C, the surface modifier density was calculated from the weight loss of the reacted modifier at the silica surface. With a decrease in the solvent polarity (in the order of acetone, toluene, and hexane), the surface modifier density increased. Hexane and toluene have similar solvent polarities. However, behavior of the surface modifier density as a function of the modifier amount was totally different. By considering the solubility of the modifier in the solvents, hexane has a higher solute ability for the modifier than toluene. The reaction between the modifier and silica was promoted in hexane, but not promoted in toluene. In addition to the solvent property, adsorbed water on the silica surface is important for the reaction. In hexane and toluene, the amounts of adsorbed water at the silica surface showed the maximum surface modifier density of about 30 mg and 50 mg, respectively. It can be postulated that the adsorbed water layer could be fixed in hexane while diffused in toluene. Based on these results, it can be concluded that the solvent polarity, solubility of the modifier, and adsorbed water amount at the silica surface should be considered in order to achieve the desired surface modification. [ABSTRACT FROM AUTHOR]

Adsorbed water films commonly coat mineral surfaces in unsaturated soils and rocks, reducing flow and transport rates. Therefore, it is important to understand how adsorbed film thickness depends on matric potential, surface chemistry, and solution chemistry. Here the problem of adsorbed water film thickness is examined by combining capillary scaling with the Derjaguin-Landau-Verwey-Overbeek (DLVO) theory. Novel aspects of this analysis include determining capillary influences on film thicknesses and incorporating solution chemistry-dependent electrostatic potential at air-water interfaces. Capillary analysis of monodisperse packings of spherical grains provided estimated ranges of matric potentials where adsorbed films are stable and showed that pendular rings within drained porous media retain most of the 'residual' water except under very low matric potentials. Within drained pores, capillary contributions to thinning of adsorbed films on spherical grains are shown to be small, such that DLVO calculations for flat surfaces are suitable approximations. Hamaker constants of common soil minerals were obtained to determine ranges of the dispersion component to matric potential-dependent film thickness. The pressure component associated with electrical double-layer forces was estimated using the compression and linear superposition approximations. The pH-dependent electrical double-layer pressure component is the dominant contribution to film thicknesses at intermediate values of matric potential, especially in lower ionic strength solutions (<10 mol m−3) on surfaces with higher-magnitude electrostatic potentials (more negative than ≈−50 mV). Adsorbed water films are predicted to usually range in thickness from ≈1 to 20 nm in drained pores and fractures of unsaturated environments. [ABSTRACT FROM AUTHOR]

Abstract: The states of water and OH groups on the surface of amorphous nanosilica with heat treatment at different temperature for hours were studied by thermogravimetry (TG), differential scanning calorimetry (DSC) and Fourier-transform infrared (FT-IR) spectroscopy. The physically adsorbed water, OH groups on surface and OH groups below surface were removed mainly at 343, 709, and 1210K, respectively. With the increasing temperature in DSC curves, the physically adsorbed water was removed firstly; secondly OH groups on surface were dehydrated; lastly were OH groups below the surface. In a wide temperature range, the dehydration of the three kinds of water took place at the same time. According to the surface area and TG results, the H2O density and OH group density on surface were obtained. For the sample without heat treatment, the physically adsorbed water and OH groups on surface were 9.80 and 8.20nm−2, respectively. And the physically adsorbed water and OH groups of the sample with heat treatment at 1273K were about 0 and 2.50nm−2, respectively. [Copyright &y& Elsevier]

Abstract: In this article the “titanium oxide/electrolyte solution” interface is studied by taking in advantage the recent developments in the field of Surface and Interface Chemistry relevant to this oxide. Ab-initio calculations were performed in the frame of the DFT theory for estimating the charge of the titanium and oxygen atoms exposed on the anatase (1 0 1), (1 0 0), (0 0 1), (1 0 3) f and rutile (1 1 0) crystal faces. These orientations have smaller surface energy with respect to other ones and thus it is more probable to be the real terminations of the anatase and rutile nanocrystallites in the titania polycrystalline powders. Potentiometric titrations for obtaining “fine structured” titration curves as well as microelectrophoresis and streaming potential measurements have been performed. On the basis of ab-initio calculations, and taking into account the relative contribution of each crystal face to the whole surface of the nanocrystals involved in the titania aggregates of a suspension, the three most probable surface ionization models have been derived. These models and the Music model are then tested in conjunction with the “Stern–Gouy–Chapman” and “Basic Stern” electrostatic models. The finally selected surface ionization model (model A) in combination with each one of the two electrostatic models describes very well the protonation/deprotonation behavior of titania. The description is also very good if this model is combined with the Three Plane (TP) model. The application of the “A/(TP)” model allowed mapping the surface (hydr)oxo-groups [TiO(H) and Ti2O(H)] of titania exposed in aqueous solutions. At pH>pzc almost all terminal oxygens [TiO] are non-protonated whereas even at low pH values the non-protonated terminal oxygens predominate. The acid-base behavior of the bridging oxygens [Ti2O] is different. Thus, even at pH=10 the greater portion of them is protonated. The application of the “A/TP” model in conjunction with potentiometric titrations, microelectrophoresis and streaming potential experiments allowed mapping the “titania/electrolyte solution” interface. It was found that the first (second) charged plane is located on the oxygen atoms of the first (second) water overlayer at a distance of 1.7 (3.4) Å from the surface. The region between the surface and the second plane is the compact layer. The region between the second plane and the shear plane is the stagnant diffuse part of the interface, with an ionic strength dependent width, ranging from 20 (0.01 M) up to 4 Å (0.3 M). The region between the shear plane and the bulk solution is the mobile diffuse part, with an ionic strength dependent width, ranging from 10 (0.01 M) up to 2 Å (0.3 M). At I >0.017 M the mean concentration of the counter ions is higher in the stagnant than in the mobile part of the diffuse layer. For a given I, removal of pH from pzc brings about an increase of the mean concentration in the interfacial region and a displacement of the counter ions from the mobile to the stagnant part of the diffuse layer. The mean concentration of the counter ions in the compact layer is generally lower than the corresponding ones in the stagnant and mobile diffuse layers. The mobility of the counter ions in the stagnant layer decreases as pH draws away from pzc or ionic strength increases. [Copyright &y& Elsevier]

Abstract: ATR-FTIRAS measurements were conducted to investigate nature of water molecules co-adsorbed with CO on highly dispersed PtRu alloy and Pt catalysts supported on carbon black in the temperature range between 23°C and 60°C. Each catalyst was uniformly dispersed and fixed by Nafion® film of 0.0125μm thickness on a chemically deposited gold film. Adsorption of CO was conducted and monitored by ATR-FTIRAS for 30min in 1% CO saturated 0.1M HClO4 after stepping the potential from 1.2V and 1.0V to 0.05V on Pt/C and PtRu/C, respectively. Similar atop and bridge bonded CO bands were observed on both PtRu/C and Pt/C, but a smaller relative band intensity, bridge bonded vs. atop CO, was observed on PtRu/C compared to Pt/C. A distinct O–H stretching band was found around 3643cm−1 and 3630cm−1 on PtRu/C and Pt/C, respectively, upon CO adsorption. They are assigned to non-hydrogen bonded water molecules co-adsorbed with CO on these catalysts. We found that the number of non-hydrogen bonded water molecules co-adsorbed with a given number of CO molecules decreases with increasing temperature and is higher on PtRu/C than Pt/C at each temperature. We interpret the higher ability of water co-adsorption at PtRu/C over Pt/C is due to stronger H2O–metal interactions on the alloy surface. We present a model of the CO–H2O co-adsorbed layer based on the bilayer model of water on metal surfaces. [Copyright &y& Elsevier]

Abstract: Surface scientists are dealing more and more with complex systems that are challenging to investigate from both experimental and theoretical perspectives. The surface science of complex interfaces, such as environmental interfaces under ambient conditions of temperature and relative humidity, requires both advances in experimental and theoretical methods in order for conceptual insights to emerge. In this prospective, several aspects of environmental interfaces and the field of environmental surface science are discussed. These include: (i) adsorbed water on oxide and carbonate interfaces; (ii) surface chemistry of oxide and carbonate interfaces in the presence of co-adsorbed water; (iii) solvation of ions by co-adsorbed water on environmental interfaces; and (iv) research needs and challenges in environmental surface science. [Copyright &y& Elsevier]

Abstract: Elecrochemical ATR-FTIRAS measurements were conducted for the first time to investigate nature of CO adsorbed under potential control on a highly dispersed Pt catalyst with average particle size of 2.6nm supported on carbon black (Pt/C) and carbon un-supported Pt black catalyst (Pt-B). Each catalyst was uniformly dispersed by 10μgPt/cm2 and fixed by Nafion® film of 0.05μm thick on a gold film chemically deposited on a Si ATR prism window. Adsorption of CO was conducted at 0.05V on the catalysts in 1 and 100% CO atmospheres, for which CO coverage, θ CO, was 0.69 and 1, respectively. Two well-defined ν(CO) bands free from band anomalies assigned to atop CO (CO(L)) and symmetrically bridge bonded CO (CO(B)sym.) were observed. It was newly found that the CO(L) band was spitted into two well-defined peaks, particularly in 1% CO, from very early stage of adsorption, which was interpreted in terms of simultaneous occupation of terrace and step-edge sites, denoted as CO(L)terrace and CO(L)edge, respectively. This simultaneous occupation was commonly observed in our work both on Pt/C and Pt-B. A new band was also observed around 1950cm−1 in addition to the bands of CO(L) and CO(B)sym., which was assigned to asymmetric bridge CO, CO(B)asym., adsorbed on (100) terraces, based on our previous ECSTM observation of CO adsorption structures on (100) facet. The CO(B)asym. on the Pt/C, particularly in 100% CO atmosphere, results in growth of a sharp band at 3650cm−1 accompanied by a concomitant development of a band around 3500cm−1. The former and the latter are assigned to ν(OH) vibrations of non-hydrogen bonded and hydrogen bonded water molecules adsorbed on Pt, respectively, interpreted in term of results from a bond scission of the existing hydrogen bonded networks by CO(L)s and from a promotion of new hydrogen bonding among water molecules presumably by CO(B)asym.. It was found that the frequency ν(CO) of CO(L) both on Pt/C and Pt-B is lower than that on bulky polycrystalline electrode Pt(poly) or different crystal planes of Pt single-crystal electrodes by 30–40cm−1 at corresponding potentials, which implies a stronger electronic interaction between CO and Pt nano-particles and/or an increased contribution of step-edge sites on the particles. Determination of the band intensities of CO(L), CO(B)asym. and CO(B)sym. has led us to conclude a much higher bridged occupation of sites at Pt nano-particles than Pt(poly) electrodes. [Copyright &y& Elsevier]

Abstract: We present experimental data acquired by diffuse reflectance infrared spectroscopy in the mid-IR (4000–400 cm−1), on micrometric-sized mineral grain powders. The spectral evolution of the OH-stretching band is followed when the adsorbed water film is thinned under dry conditions, from high to low hydration states. The IR bands are found to be characteristic of the degree of adsorption/confinement of the liquid water. The OH-stretching band is shifted toward shorter wavenumbers than in bulk water, showing that a significant portion of adsorbed water has a higher intermolecular bonding energy. Complementary treatment of the kinetics of water desorption, varying with the surface forces in the water film, confirms the relationships of these bands with the constrained water state. We distinguish different water types obeying liquid–liquid interactions (free and capillary water) or dominated by solid–water interactions (confined and adsorbed water). Part of this study is devoted to mesoporous silica MCM-41, of interest due to the restricted geometries of its mesopores (4.7 nm) favouring the confined water state. The methodology allows us to distinguish bulk and adsorbed/confined water, using spectral analysis coupled with an understanding of the dynamic behaviour of the desorption process. [Copyright &y& Elsevier]

Water-vapor adsorption on poorly crystalline boehmite (PCB) was studied using a gravimetric FTIR apparatus that measured FTIR spectra and water adsorption isotherms simultaneously. The intensity of the δ(HOH) band of adsorbed water changed linearly with water content and this linear relationship was used to determine the dry mass of the sample. Adsorption and desorption isotherms of PCB showed a Type IV isotherm. The BETH2O surface area of PCB was 514±36 m2/g. The mean crystallite dimensions of PCB were estimated to be 4.5×2.2×10.0 nm (dimensions along the a, b, and c axes, respectively) based on application of the Scherrer equation to powder diffraction data of PCB. A surface area value of 504±45 m2/g calculated using the mean crystallite dimensions was in good agreement with the BETH2O surface area. This work also demonstrated a method to determine surface areas for materials with minimal perturbation of their surface structure. In addition, the FTIR spectra of PCB were influenced by changes in water content. The δ(AlOH) band at 835 cm−1 observed under dry conditions was assigned to the non-H-bonded surface OH groups. As the amount of adsorbed water increased, the intensity at 835 cm−1 decreased and that at 890 and 965 cm−1 increased. The 890- and 965-cm−1 bands are assigned to surface OH groups H-bonded with adsorbed water. [Copyright &y& Elsevier]

The effect of surface chemistry on the tribological performance and reliability of a MEMS lateral output motor is reported. Relative humidity (RH) and octadecyltrichlorosilane (OTS) self-assembled monolayer (SAM) coatings were used to change surface chemistry. Electrical and tribological performance of uncoated and OTS-coated motors were found to be dependent on RH. For uncoated motors, excessive wear of sliding contacts and welding (permanent adhesion) of static contacts were observed at 0.1% RH. Degradation of electrostatic force and high static friction (stiction) forces limited dynamic performance and reliability and caused device sticking at and above 70% RH. Around 50% RH, uncoated motors exhibited negligible wear, low adhesion, and a wear life at least three orders of magnitude longer than in the dry environment (experiments were stopped without failure after about one billion cycles). Water vapor behaved as a gas phase replenishable lubricant by providing a protective adsorbed film. The OTS coating broadened the operating envelope to 30–50% RH and reduced stiction, which allowed better dynamic performance at high RH. The OTS coating improved durability at 0.1% RH, but it was still poor. At high RH, stiction problems reoccurred when the OTS coating was worn away. By controlling and balancing surface chemistry (adsorbed water and OTS), excellent performance, low friction and wear, and excellent durability were attained with the lateral output motor. [ABSTRACT FROM AUTHOR]

Abstract: In this communication we present topographic images of the Pt(111) surface in CO saturated 0.1M HClO4, obtained by scanning tunneling microscopy. The topography presents two different structures, depending on the CO adsorption potential (E ad =0.15V or E ad =0.5V vs RHE). For adsorption at 0.15V the system presents a heterogeneous appearance, which totally covers the surface and impedes the observation of steps on the substrate surface. When CO is adsorbed at 0.5V large clusters forming chains along the steps are observed. These aggregates can be, tentatively, correlated with the H-bonded water structure suggested earlier on the basis of FTIR spectroscopy. The clusters have inhibitory effects on CO oxidation. [Copyright &y& Elsevier]