Size- and support-dependency in the catalysis of gold

The application of ellipsometry of the study of the adsorption behavior of proteins and synthetic macromolecules at the air-water interface has been investigated. It is shown that for macromolecules the amount adsorbed per unit area, Γ, as determined by ellipsometry, only has a well-defined physical meaning if the refractive-index increment remains constant up to high concentrations present in the adsorbed layer. It has been found experimentally that this conditioned is fulfilled for proteins. The ellipsometric Γ values of some protein agree satisfactorily with those obtained by two independent techniques has been used to investigate the adsorption from solution of κ-casein, bovine serum albumin, and polyvinyl alcohol. For bovine serum albumin, Γ reaches a plateau value of 2.9 mg/m2 for concentrations ≥ 0.05 wt%. The thickness of the adsorbed molecules. For κ-casein, Γ steadily increases with increasing centration and multilayers are formed. The technique provides interesting information on conformational changes in adsorbed macromolecules, on the rate of the process, and on the conditions under which these occur.

Ellipsometry as a tool to study the adsorption behavior of synthetic and biopolymers at the air–water interface

It is generally accepted that supported graphene is hydrophobic and that its water contact angle is similar to that of graphite Here, we show that the water contact angles of freshly prepared supported graphene and graphite surfaces increase when they are exposed to ambient air By using infrared spectroscopy and X-ray photoelectron spectroscopy we demonstrate that airborne hydrocarbons adsorb on graphitic surfaces, and that a concurrent decrease in the water contact angle occurs when these contaminants are partially removed by both thermal annealing and controlled ultraviolet-O3 treatment Our findings indicate that graphitic surfaces are more hydrophilic than previously believed, and suggest that previously reported data on the wettability of graphitic surfaces may have been affected by unintentional hydrocarbon contamination from ambient air

Effect of airborne contaminants on the wettability of supported graphene and graphite

The term superhydrophilicity is only 11–12 years old and was introduced just after the explosion of research on superhydrophobic surfaces, in response to the demand for surfaces and coatings with exceptionally strong affinity to water. The definition of superhydrophilic substrates has not been clarified yet, and unrestricted use of this term to hydrophilic surfaces has stirred controversy in the last few years in the surface chemistry community. In this review, we take a close look into major definitions of hydrophilic surfaces used in the past, before we review the physics behind the superhydrophilic phenomenon and make recommendation on defining superhydrophilic surfaces and coatings. We also review chemical and physical methods used in the fabrication of substrates on surfaces of which water spreads completely. Several applications of superhydrophilic surfaces, including examples from the authors' own research, conclude this review.

Hydrophilic and superhydrophilic surfaces and materials

The strength of the thiol-gold interactions provides the basis to fabricate robust self-assembled monolayers for diverse applications. Investigation on the stability of thiol-gold interactions has thus become a hot topic. Here we use atomic force microscopy to quantify the stability of individual thiol-gold contacts formed both by isolated single thiols and in self-assembled monolayers on gold surface. Our results show that the oxidized gold surface can enhance greatly the stability of gold-thiol contacts. In addition, the shift of binding modes from a coordinate bond to a covalent bond with the change in environmental pH and interaction time has been observed experimentally. Furthermore, isolated thiol-gold contact is found to be more stable than that in self-assembled monolayers. Our findings revealed mechanisms to control the strength of thiol-gold contacts and will help guide the design of thiol-gold contacts for a variety of practical applications.

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Quantifying thiol-gold interactions towards the efficient strength control

The hydrophilic nature of a clean gold surface

Ellipsometer, surface-tension, and contact-potential measurements were made simultaneously at and below monolayer coverage (θ = 1 to 0.05) on a clean mercury surface at room temperature. It has been demonstrated with molecules of known dimensions (caproic, lauric, stearic, behenic, and adamantane-carboxylic acids, and α bromonaphthalene and pentane) that the classical Drude equation for the relationship between the phase shift ( Δ¯ − Δ) of reflected polarized light and the average effective film thickness d is valid below monolayer coverage. This is so even though the Drude equation was derived for thick films that are considered to be a continuum with index and density independent of thickness. The equation for the three-dimensional model is Δ¯ − Δ = αd, where for less than monolayer coverage d is the hypothetical thickness the film would have if it were a continuum with index and density independent of d. The equation for the 3-D model remains valid below monolayer coverage, where the continuum property is not approximated, because the 2-D model gives essentially the same equation Δ¯ − Δ = αd0θ. In the 2-D model, the molecules are contained between the substrate surface and a plane d0A above the surface, where d0 is the molecular diameter. The phase shift ( Δ¯ − Δ) decreases as the fraction of the surface covered (θ) decreases because the index of refraction is a function of the surface density. Values of α, calculated with the bulk-liquid index of refraction (sodium D line) and the first-order Drude relation (for films with only a real part of the refractive index) can be used to calculate d (0.05d0 to d0) or θ (0.05 to 1) within a few percent with the equations above. The same values are obtained if the relationship between α and the film index (based on the 2-D model) is used to calculate α. The ellipsometer measurements indicate changes of orientation of the molecules on the surface. A technique is described for automatically recording ellipsometer measurements for very thin films (0–30 A).

Tennyson Smith

Papers

The hydrophilic nature of a clean gold surface

Ellipsometry for Measurements at and below Monolayer Coverage

Oxidation of titanium between 25°C and 400°C

Monomolecular films on mercury

Auger electron spectroscopy and ion sputter profiles of oxides on aluminum