Pressure jump water interface

Hayes and Leckie (1986) postulate on the basis of their pressure jump relaxation experiments on the adsorption-desorption of Pb2+ at the goethite-water interface the following mechanism ... 

Due to the fast kinetics of adsorption/desorption reactions of inorganic ions at the oxide/aqueous interface, few mechanistic studies have been completed that allow a description of the elementary processes occurring (half lives < 1 sec). Over the past five years, relaxation techniques have been utilized in studying fast reactions taking place at electrified interfaces (1-7). In this paper we illustrate the type of information that can be obtained by the pressure-jump method, using as an example a study of Pb2+ adsorption/desorption at the goethite/water interface. 

Based on the pressure-jump relaxation results reported here, the following mechanism is postulated for the adsorption/desorption of Pb2+ ion at the goethite/water interface (8) ... 

Zhang, P.C. Sparks, D.L. (1989) Kinetics and mechanism of molybdate adsorption/desorp-tion at the goethite/water interface using pressure-jump relaxation. Soil Sci. Soc. Am. 

Zhang, P.C. Sparks, D.L. (1990) Kinetics and mechanism of sulfate adsorption and desorption on goethite using pressure jump relaxation. Soil Sci. Soc. Am. J. 54 1266-1273 Zhang, P.C. Sparks, D.L. (1990) Kinetics of selenate and selenite adsorption/desorption at the goethite/water interface. Environ. Sci. Technol. 24 1848-1856... 

Pure oil/protein solution systems The Interfacial Displacement Tensiometer was used to examine the effect of additives known to promote an appreciable interfacial rheology. The systems selected were Toluene/a-lactalbumin (100 ppm), toluene/BSA (100 ppm), and nonane/BSA (100 ppm) these systems were expected to produce highly visco-elastic interfacial films. The BSA solution when displaced by either toluene or nonane (see Figure 11) gave rise to pressure jumps on the I.D.T. traces at points equivalent to entry and exit of the narrower capillary. These peaks indicate an increased resistance to displacement of the interface associated with its deformation and changes of extent. The maximum pressures are considerably in excess of those given by the pure oil/water reference system, also shown in Figure 11. 

A second example involves reflectance infrared spectroscopic structural analysis of polydimethylsiloxane at the air-water interface. Surface pressure versus surface area or surface concentration isotherms of polydimethylsiloxane on water have been studied since 1947 at least (223). Upon compression, the isotherm begins at zero surface pressure at surface concentrations significantly below 0.75 mg/m. Around f 1 0.75 mg/m, the surface pressure tt jumps substantially to about 9 mN/m, where it exhibits a plateau until about T2 1.6 mg/m, where a small Tt jump occurs followed by a smaller rise (Fig. 31). Structural features associated with the various transitions have often been debated. Particular controversy is associated with the ix plateau aroimd 9 mN/m between Fi and T2 (224,225). In conjimction with other techniques, such as epifluorescence microscopy, external reflectance infrared spectroscopy was used to study microstructural features (coexistence of two phases) of polydimethylsiloxane CH3—[Si(CH3)2—Oln—SKCHala, spread at the air-water interface in the vicinity of the n plateau at 9 mN/m (226). A broad band containing several components is foimd in the 1000-1100 cm ... 

The catalytic reactions at solid-liquid interfaces of metal oxides have been of great interest to colloid chemists. The adsorption-desorption phenomena of various metal ions on oxides such as Y-AI2O3 have been extensively investigated since adsorption-desorption is a fundamental step in heterogeneous catalytic reactions. Several mechanisms have been proposed by many investigators . Kinetic studies, however, have scarcely been carried out because the reaction is too fast to be measured by ordinary methods. Only a kinetic study on the proton adsorption-desorption at the Ti02-water interface has been reported using the pressure-jump technique by the present authors. ... 

Example 5.15 Effect of Microporous Layer Often, to enhance water transport, a special highly hydrophobic coating between the DM and catalyst layer will be used, called the microporous layer (MPL). This layer has an average pore size somewhere between that of the catalyst layer and the macro-DM. Consider a bilayered DM coated with an MPL. In equilibrium, there will be a liquid saturation jump at the interface between the MPL and the DM, because of the discontinuity in pore sizes. That is, in order to have a liquid phase pressure balance at the MPL-DM interface, as required for equilibrium, the saturation in the MPL will be lower, since the pore size is lower, increasing the capillary pressure. Assume... 

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