Solid/aqueous solution interfaces

General Observations About x. its Relationship to the Overall Partitioning Coefficient and to the Concept of Surface-Site Heterogeneity. One approach to metal/particle surface interactions which has been developed, historically, in a variety of forms, is a conceptual model that assumes only two conditions for surface sites occupied by an adsorbate or unoccupied. In applying this approach to the solid/aqueous solution interface, the adsorption... 

We now extend the work to in situ measurements on metal ions adsorbed at the metal oxide/aqueous solution interface. In this report, our previous results are combined with new measurements to yield specific information on the chemical structure of adsorbed species at the solid/aqueous solution interface. Here, we describe the principles of emission Mossbauer spectroscopy, experimental techniques, and some results on divalent Co-57 and pentavalent Sb-119 ions adsorbed at the interface between hematite (a-Fe203) and aqueous solutions. 

Electric Double Layer at Solid/Aqueous Solution Interfaces... 

The mechanism of interaction of amino acids at solid/ aqueous solution interfaces has been investigated through adsorption and electrokinetic measurements. Isotherms for the adsorption of glutamic acid, proline and lysine from aqueous solutions at the surface of rutile are quite different from those on hydroxyapatite. To delineate the role of the electrical double layer in adsorption behavior, electrophoretic mobilities were measured as a function of pH and amino acid concentrations. Mechanisms for interaction of these surfactants with rutile and hydroxyapatite are proposed, taking into consideration the structure of the amino acid ions, solution chemistry and the electrical aspects of adsorption. 

X-ray standing wave studies of the electrical double layer at solid-aqueous solution interfaces and in situ measurements of surface reactivity... 

The most general feature of the adsorption behavior of metal ions at solid-aqueous solution interfaces is the abrupt rise in adsorption over a narrow pH range. This has been illustrated, for example, for manganese adsorption on glass (2), cobalt on hydrous ferric oxide (8), manganese on hydrous manganese oxide (12), protactinium on glass (14), and... 

This experimental evidence clearly shows the complicated nature of the adsorption isotherm for a detergent at the polar solid-aqueous solution interface. 

Dirt particles spontaneously leave a solid surface if it is energetically favorable to replace the dirt-solid interface (SD) by two interfaces the dirt-aqueous solution interface (DW) and the solid-aqueous solution interface (SW). Here, the solid is a textile fibre or any other material, which we want to clean (Fig. 7.22). The change in the Gibbs free energy... 

In mineral processing, there are numerous systems in which postulates have been made to suggest adsorption of surface active molecules on specific surface sites. Most of the postulates are based on inference from a variety of observations and direct evidence has been lacking. It should now be possible to use Raman spectroscopy to characterize solid/aqueous solution interfaces. 

The phenomena presented in this book were discussed in many reviews. For example, Schwarz [13] discussed methods used to characterize the acid base properties of catalysts. The review on sorption on solid - aqueous solution interface by Parks [14] includes also principles of surface science. The book Environmental Chemistry of Aluminum edited by Sposito reviews the solution and surface chemistry of aluminum compounds. Chapter 3 [15] provides thermochemical data for aluminum compounds. Chapter 5 [16] lists the points of zero charge of aluminum oxides, oxohydroxides and hydroxides with many references on adsorption of metal cations and various anions on these materials. Unlike the present book, which is confined to sorption from solution at room temperature, publications on coprecipitation and adsorption from gas phase or at elevated temperatures are also cited there. Brown et al. [17] reviewed on dry and wet surface chemistry of metal oxides. Stumm [18] reviewed sorption of ions on iron and aluminum oxides. The review by Schindler and Stumm [19] is devoted to surface charging and specific adsorption on oxides. Schindler [19] published a review on similar topic in German. Many other reviews related to specific topics are cited in respective chapters. 

Another extreme is to neglect the exponential term in Eq. (5.24) at all. This leads to overestimated effect of the pH on tjo (assuming a fixed value). A model neglecting the surface potential is physically unrealistic, but non-electrostatic models of adsorption at solid-aqueous solution interface can be found even in very recent literature. According to the prevailing opinion the actual surface potential is between the above two extremes (Nemst potential and 0 = 0). The electrostatic models of oxide - inert electrolyte solution interface were discussed in detail by Westall and Hohl [25]. In this section the most common electrostatic models are combined with the 1-pK model in order to illustrate their ability to simulate the actual surface charging data. 

Shchukarev, A., XPS at solid-aqueous solution interface, Adv Colloid Interf. Sci., 122, 149, 2006,... 

Perfluoroalkyl chain surfactants are much poorer wetting agents than alkyl chain surfactants for both paraffin and polymethyl methacrylate surfaces (Pyter, 1982). One explanation may be the mutual phobicity of alkyl and perfluoroalkyl chains, causing perfluoroalkyl chain surfactants to be adsorbed more poorly than alkyl chain surfactants at these solid-aqueous solution interfaces. 

For a series of lV-alkyl-2-pyrrolidinones that produce enhanced superspreading of the POE trisiloxane mentioned above on polyethylene film, it has been shown (Rosen, 2001) that the addition of the alkylpyrrolidinone to the trisiloxane surfactant produces little or no increase in the total surfactant at the hydrophobic solid-air or aqueous solution-air interfaces, but a considerable increase in the total surfactant adsorption at the hydrophobic solid-aqueous solution interface. This enhanced adsorption of surfactant at the aqueous solution-solid interface relative to that at the aqueous solution-air interface produces a decrease in the surfactant concentration at the air-solution interface in the thin precursor film at the wetting front (Figure 6-8). This results in a surface tension gradient in the precursor film promoting movement of the aqueous phase to the wetting front. 

The order of increased surfactant adsorption on the solid produced by the different alkyl pyrrolidinones parallels the order of their enhancement of superspreading. In addition, it was shown (Wu, 2002) (1) that the change in the spreading coefficient (equation 6.1) parallels enhancement of superspreading and (2) that the order of increased attractive molecular interaction between the different alkylpyr-rolidinones and the trisiloxane surfactant at the hydrophobic solid-aqueous solution interface, as measured by the interaction parameter Psl° (Chapter 11) n-butyl < n-cyclohexyl < -octyl < n-hexyl < 2-ethylhexyl, is exactly the same order as that of their enhancement of the superspreading. 

Recently, it has been found that aqueous solutions of two different hydrocarbon chain surfactants can also show superspreading on highly hydrophobic substrates (Rosen, 2002 Zhou, 2003). In these mixtures, the two different hydrocarbon-chain surfactants also interact to produce synergistic enhancement of the total surfactant adsorption at the hydrophobic solid-aqueous solution interface relative to that at the air-aqueous solution interface, and this is accompanied by an enhanced rate of reduction of the contact angle (Zhou, 2003). SF values for these mixtures are also listed in Table 6-3. 

Equilibrium reactions at the solid-aqueous solution interface may be characterized by those in which oxidation or reduction does or does not occor, A reaction without oxidation or reduction may be repreaenred by the reaction... 

In studies of surfactant adsorption at the solid-aqueous solution interface one uncovers interesting features related to the shape of adsorption isotherms in the region corresponding to high surfactant concentrations [15]. Let us discuss the shape of the adsorption isotherm by describing the adsorption in the whole range of surfactant concentrations (from x = 0 to x = 1) from a solution containing infinitely miscible components. To do so, let s compare the surfactant concentration at the surface, x(s), and in the bulk, x. 

Figure 3 The solid/aqueous solution interface and electrical double layer for a hydrolyzed oxide surface o, charge density V /, electrostatic potential +, cation anion, 0, surface c, compact layer d, diffuse layer.

As depicted in Figure 4.5, the surfactant bilayer created at the solid/aqueous solution interface provides hydrophobic loci for the solubilization of monomer or radicals these can polymerize further on the modified inorganic surface and effectively coat the sohd particles according to an emulsion-like polymerization reaction. Three steps are involved in the coating reaction. In the first step, the emulsifier adsorbs onto the mineral surface, forming micelle-like aggregates. In a second step, the monomer is solubihzed in the adsorbed micelles. Finally, the polymerization takes place as a conventional emulsion polymerization in the monomer-sweUed admiceUes (Fig. 4.6). 

Our approach to this problem is to consider an interface comprised of an arbitrary heterogeneous distribution of binding sites and use experimental data directly to reveal any extent of heterogeneity. We apply this to proton transfer processes at the solid/aqueous solution interface of metal (hydr)oxides that are commonly used as catalyst supports. The results of our analysis yield the charging behavior of the substrate as a function of the proton concentration in the bulk solution. We use protons as probe... 

Abraham T, Giasson S, Gohy JF, Jerome R, Muller B, Stamm M (2000) Adsorption kinetics of a hydrophobic-hydrophilic diblock polyelectrolyte at the solid-aqueous solution interface a slow birth and fast growth process. Macromolecules 33 6051-6059... 

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