Photothermal Atomic Force Microscopy Coupled with Infrared Spectroscopy (AFM-IR) Analysis of High Extinction Coefficient Materials: A Case Study with Silica and Silicate Glasses.

Photothermal atomic force microscopy coupled with infrared spectroscopy (AFM-IR) brings significant value as a spatially resolved surface analysis technique for disordered oxide materials such as glasses, but additional development and fundamental understanding of governing principles is needed to interpret AFM-IR spectra, since the existing theory described for organic materials does not work for materials with high extinction coefficients for infrared (IR) absorption. This paper describes theoretical calculation of a transient temperature profile inside the IR-absorbing material considering IR refraction at the interface as well as IR adsorption and heat transfer inside the sample. This calculation explains the differences in peak positions and amplitudes of AFM-IR spectra from those of specular reflectance and extinction coefficient spectra.

Estimating Internal Stress of an Alteration Layer Formed on Corroded Boroaluminosilicate Glass through Spectroscopic Ellipsometry Analysis.

Aqueous corrosion of glass may result in the formation of an alteration layer in the glass surface of which chemical composition and network structure are different from those of the bulk glass. Since corrosion occurs far below the glass-transition temperature, the alteration layer cannot fully relax to the new structure with the lowest possible energy. Molecular dynamics simulations suggested that such a network will contain highly strained chemical bonds, which can be manifested as a stress in the alteration layer.

Competitive Adsorption of Lubricant Base Oil and Ionic Liquid Additives at Air/Liquid and Solid/Liquid Interfaces.

Oil-soluble ionic liquids (ILs) have been proved as effective additives in lubricant oils through tribological experiments and post-test analytical analyses. In this study, surface structures of lubricant base oil, oil-soluble ILs, and their mixtures at the air/liquid and solid/liquid interfaces have been studied using sum frequency generation (SFG) vibrational spectroscopy. At the air/base oil and air/IL interfaces, the alkyl chains of the studied compounds were shown to be conformationally disordered and their terminal methyl groups point outward at the liquid surface.

Ultralow Boundary Lubrication Friction by Three-Way Synergistic Interactions among Ionic Liquid, Friction Modifier, and Dispersant.

Interactions among antiwear additives (AWs), friction modifiers (FMs), and dispersant in a lubricating oil are critical for tribological performance. This study investigates compatibilities of three oil-soluble ionic liquids (ILs, candidate AWs) with an FM, molybdenum dithiocarbamate (MoDTC), and a dispersant, polyisobutene succinimide (PIBSI) under boundary lubrication. Either synergistic or antagonistic effects were observed depending on the IL's chemistry.

Self-accelerated corrosion of nuclear waste forms at material interfaces.

The US plan for high-level nuclear waste includes the immobilization of long-lived radionuclides in glass or ceramic waste forms in stainless-steel canisters for disposal in deep geological repositories. Here we report that, under simulated repository conditions, corrosion could be significantly accelerated at the interfaces of different barrier materials, which has not been considered in the current safety and performance assessment models. Severe localized corrosion was found at the interfaces between stainless steel and a model nuclear waste glass and between stainless steel and a ceramic waste form.

Dependence of water adsorption on the surface structure of silicon wafers aged under different environmental conditions.

Most materials exposed to ambient air can adsorb water molecules and the adsorption capability strongly depends on the surface property. The water contact angle has been widely used as a measure for surface wettability; however, a question can still be asked whether the water contact angle can be used as an adequate sole predictor for water adsorption on the surface in humid air. In this paper, HF-etched silicon wafers were aged (oxidized) under different environmental conditions at room temperature to grow surface layers with varying water contact angles from ∼0° (fully hydrophilic) to ∼83° (highly hydrophobic), and water adsorption as a function of relative humidity (RH) was studied on such surfaces.

Mechanochemical Reactions of Adsorbates at Tribological Interfaces: Tribopolymerizations of Allyl Alcohol Coadsorbed with Water on Silicon Oxide.

Mechanochemical reactions of adsorbed molecules at tribological interfaces can benefit or impede lubrication, depending on the type of reactions induced by the interfacial shear or friction. Shear-induced polymerization of oxidatively chemisorbed organic species can occur at tribological interfaces, and their products can mitigate the wear of the surface in the case of the intermittent cessation of the lubricant supply. In contrast, tribochemical reactions involving water molecules impinging from the ambient air could facilitate surface wear.

Sum Frequency Generation Imaging Microscopy of Self-Assembled Monolayers on Metal Surfaces: Factor Analysis of Mixed Monolayers.

Sum frequency generation (SFG) images of microcontact patterned self-assembled alkanethiol monolayers on metal surfaces were analyzed by factor analysis (FA) to determine the spatial distribution of the patterned monolayers over the images. Additionally, each significant abstract factor produced by FA was assessed to determine the information contained within it. These results indicate that FA of the SFG spectra is a promising method to determine the composition and identities of mixed alkanethiol systems that show different vibrational spectra and image contrast.

Adsorption of Dimethyldodecylamine Oxide and Its Mixtures with Triton X-100 at the Hydrophilic Silica/Water Interface Studied Using Total Internal Reflection Raman Spectroscopy.

Adsorption of dimethyldodecylamine oxide (DDAO) and its mixtures with Triton X-100 (TX-100) at the hydrophilic silica/water interface has been studied using total internal reflection (TIR) Raman spectroscopy and target factor analysis (TFA). The use of a linear vibrational spectroscopic technique helps obtain information on molecular behavior, adsorbed amount, and conformational order of surfactant molecules at the interface. The results obtained from polarized Raman measurements of pure DDAO show insignificant changes in the orientation and conformational order of surface molecules as a function of DDAO bulk concentrations.