Surface-chemical explanation

In concentrated emulsions and foams the thin liquid films that separate the droplets or bubbles from each other are very important in determining the overall stability of the dispersion. In order to be able to withstand deformations without rupturing, a thin liquid film must be somewhat elastic. The surface chemical explanation for thin film elasticity comes from Marangoni and Gibbs (see Ref. [199]). When a surfactant-stabilized film undergoes sudden expansion, then immediately the expanded... 

The model provides a chemical explanation for charge buildup on variable-charge surfaces as salt concentrations are increased in solution. The explanation is that the activities of both base, MOH, and acid, HX, are increased by the addition... 

Using pitch-based ACFs, Mochida et al. [132] reported 87% conversion at room temperatnre in dry air. Lower conversions were obtained in the presence of water vapor. The anthors found that heat treatment at 1123 K enhanced the activity of the fibers. Such treatment removes oxygen functional groups from the surface of the ACFs the vacant sites created as a result of this treatment were thought to be the active sites for the reaction. On the other hand, the hydrophobic surface obtained after the heat treatment helps to decrease the amount of water adsorbed, which decreases NO conversion in humid air. An interesting point noted by Mochida et al. [131] is that PAN- and pitch-based ACFs exhibited the reverse order of activity for the oxidation of SO2 and NO. Thus, pitch fibers were best for NO oxidation, while PAN fibers were found to be more active for SO2 oxidation. No explanation was provided by the authors for this finding, which certainly reflects the different surface chemical properties of the two fiber types. A detailed kinetic study of this process was presented in a subsequent paper [133], while Guo et al. [134] compared the performances of different carbon fibers (PAN, pitch) and activated carbons. 

Calcined barium hydroxide is an efficient catalyst for a number of base-mediated reactions. Among these, the Claisen-Schmidt condensation of acetophenones with benzaldehydes occurs in times as short as 10 min at room temperature (Eq. 15). The acetophenone enolate (detected by IR spectroscopy) is formed on the catalyst surface, where the reaction with the aldehyde takes place. The higher activity of the ketone enolate is interpreted by the authors as the result of "an increased vibrational state of the lattice", a formulation close to the mechano-chemical explanation. With the help of selective poisoning experiments, it is concluded that the enolate forms via a SET mechanism. 

FIG. 6.5 The nickel famine and a possible chemical explanation. Top The loss of nickel from ocean water predated the Great Oxidation Event 2.5 billion years ago. Bottom Melting points decrease across the second half of the transition metals, which may explain why nickel sohdified and entered the mantle, while copper and zinc remained at the surface. 

Give a chemical explanation for each of the following (a) When calcium metal is added to a sulfuric acid solution, hydrogen gas is generated. After a few minutes, the reaction slows down and eventually stops even though none of the reactants is used up. Explain, (b) In the activity series, aluminum is above hydrogen, yet the metal appears to be unreactive toward hydrochloric acid. Why Hint A1 forms an oxide, AJ2O3, on the surface.)... 

In conclusion, the surface analysis showed that the laser machined surface shows more attraction to the activation solution. This (partially) explains why, after rinsing with water, there are still activation drops on the laser machined area but not on the original polymer surface. This explanation is useful, especially when the chemical bonding mechanism is still not available. Nevertheless, our analysis does have limitations as the Young equation is based on ideal smooth surfaces. When porosity or roughness are included, factors such as interlock forces and maybe even chemical bonding may contribute to the adhesion work between the activation solution and the surface. 

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