Interface adsorbent-liquid

Environmental chemicals occur as pure liquid or solid compounds, dissolved in water or in nonaqueous liquids, volatilised in gases, dissolved in solids (absorbed) or bound to interfaces (adsorbed). Figure 5 gives a schematic view of the different physical states at which substrates are taken up by microbial cells. There is a consensus that water-dissolved chemicals are available to microbes. This is obvious for readily soluble chemicals, but there is also clear evidence for microbial uptake of the small dissolved fractions of poorly water soluble compounds. Rogoff already had shown in 1962 that bacteria take up phenanthrene from aqueous solution [55], In the intervening time many other researchers have made the same observation with various combinations of microorganisms and poorly soluble compounds [14,56,57]. 

Cb and Cs = the bulk liquid and solid-liquid interface adsorbate concentrations, respectively,... 

Many substances preferentially concentrate at interfaces, including liquid/liquid ones. Although TIRF is most easily adaptable to solid/liquid interfaces, Morrison and Weber(100) succeeded in observing the preferential adsorption of certain amphiphilic dyes at the interface between two immiscible and optically dissimilar liquids. Steady-state TIR fluorescence polarization in that system showed that the rotational diffusion of the interfa-cially adsorbed dye was restricted. 

All corrosion inhibitors in use as of this writing are oil-soluble surfactants (qv) which consist of a hydrophobic hydrocarbon backbone and a hydrophilic functional group. Oil-soluble surfactant-type additives were first used in 1946 by the Sinclair Oil Co. (38). Most corrosion inhibitors are carboxylic acids (qv), amines, or amine salts (39), depending on the types of water bottoms encountered in the whole distribution system. The wrong choice of inhibitors can lead to unwanted reactions. For instance, use of an acidic corrosion inhibitor when the water bottoms are caustic can result in the formation of insoluble salts that can plug filters in the distribution system or in customers vehicles. Because these additives form a strongly adsorbed impervious film at the metal liquid interface, low liquid concentrations are usually adequate. Concentrations typically range up to 5 ppm. In many situations, pipeline companies add their own corrosion inhibitors on top of that added by refiners. 

The adsorption of reactant molecules at the interface significantly affects the overall reaction rate in the two-phase system by the catalytic function of the interface. The liquid-liquid interface itself is a unique catalyst with such a flexible adsorbed area, which can be expanded or shrunk easily only by stirring or shaking. The increase of the adsorbed reactant molecules results in the promotion of reaction rate and the product will be extracted into the organic phase depending on its hydrophobicity. 

We can estimate the effective pressure from the potential profile molecules confined in the slitlike pore of 1 nm in width are presumed to be exposed to the high pressure of 100 MPa. Also application of the Laplace equation to estimate the pressure difference across the adsorbed liquid-gas interface gives 20 MPa for N2 and 140 MPa for H20[17]. Therefore, the graphitic micropore can offer the high pressure field from the macroscopic view. 

The classical model for describing adsorption in simple geometric pores is based on the Kelvin equation [125], which is derived from the condition of mechanical equilibrium for a curved interface between coexisting vapor and liquid phases in a pore. If the adsorbed liquid completely wets the pore walls, as shown in Fig. 17a, and the vapor phase is assumed to be an ideal gas, then mechanical equilibrium requires that... 

Slippage is very sensitive to the molecular structure of the interface, as we have already discussed. Thus, adsorption can strongly influence this phenomenon. In order to describe the effect of adsorption, let it be assumed that the adsorbed layer is rigidly attached to the surface, and slippage occurs at the adsorbate-liquid interface, see Fig. 2. Then the equation of motion of the adsorbed layer can be written as [61] ... 

Above, we discussed the situation where the adsorbed layer is rigidly attached to the oscillating crystal surface, and there is finite slippage at the adsorbate-liquid interface. An alternative model, based on the assumption that slippage occurs at the crystal-adsorbed interface and non-sUp boundary conditions apply to the adsorbate-liquid interface, can also be considered. Eor a small slip length, bs <3C 3, this model leads to the same results for the shift of the complex resonance frequency as the model discussed above and measurements employing the QCM cannot distinguish between them. How-... 

FIGURE 5 Schematic representation of macromolecules adsorbed (a) on the solid surface and (b) on the interface between liquid and quasi-liquid phases. For detailed explanation,... 

There have been attempts [53] to estimate the slip length at the solid/ liquid interface on the basis of QCM experiments for adsorbed liquid layers. The slip length can be expressed in terms of the coefficient of sliding friction, x-> at the interface... 

Consider the effect of adsorption on the parameters Awa and x- The layer adsorbed at the electrode/electrolyte interface contains two types of molecules adsorbate and solvent. In the framework of mean field approximation, the effective interaction between the liquid and the adsorbed layer can be characterized by the energy SiaTalTm + // (1 - Ta/Tm), where sia is the characteristic energy of the adsorbate/liquid interaction and is the... 

Proteins, naturally occurring macromolecular surfactants with amphiphilic nature, are adsorbed onto interfaces, thereby affecting the physical states of interfaces. Many enzymes are involved in catalytic reaction at interfaces. For enzymatic reaction at interfaces, different from the reaction in homogeneous systems, interfacial contact and subsequent conformational change of enzymes are important events determining their catalytic activity. In this chapter, I will describe the conformation of proteins and their interaction (protein-protein and protein-surfactant) at interfaces (mainly liquid-liquid interfaces). The characteristics of enzymatic reaction at liquid-liquid and solid-liquid interfaces, especially lipase reaction, wiU also be described. 

Consider a simple experiment in which a clean solid surface (free of adsorbed liquid and vapour impurities) is immersed in an excess of pure liquid (Path 1 in Fig. 6.5). If thermal effects arising from absorption, solubility, and swelling of a solid may be eliminated, the whole enthalpy change on immersion is ascribed only to the interface. Sometimes the immersion of a solid in a liquid is accompanied by the formation of an electrical double layer. For mineral oxide-water systems [51, 52], the double-layer effects (i.e., generation of surface charge by protonation or deprotonation of some surface hydroxyl groups, and adsorption of counterions in the Stern or/and diffuse layers) are clearly secondary in comparison with the basic wetting (this contribution is 10-15 % of the total heat effect, at the most). 

In this chapter, we first discuss how the bond valence method can work in a complementary manner with DFT surface calculations, similar to how they are known to complement bulk DFT calculations. We then review several known and proposed surface structures on the perovskite SrTiOs and the rock salt magnesium oxide (MgO) from a bond valence perspective. We continue to examine a few cases where, similar to solid-liquid interfaces, adsorbates from the atmosphere may be interacting with oxide surfaces. In these discussions, we will show how bond valence can explain and even predict surface reconstructions and interactions of the surface with adsorbates. Finally, we will discuss other issues present at surfaces where bond valence analysis could be of value to ongoing work. 

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