Displacement Adsorption

When the two phases in contact are condensed phases and the entire volume is taken up by incompressible substances, positive adsorption of one component must be attended by negative adsorption (desorption) of other components. This phenomenon is called adsorptive displacement. 

On the surface of metal electrodes, one also hnds almost always some kind or other of adsorbed oxygen or phase oxide layer produced by interaction with the surrounding air (air-oxidized electrodes). The adsorption of foreign matter on an electrode surface as a rule leads to a lower catalytic activity. In some cases this effect may be very pronounced. For instance, the adsorption of mercury ions, arsenic compounds, or carbon monoxide on platinum electrodes leads to a strong decrease (and sometimes total suppression) of their catalytic activity toward many reactions. These substances then are spoken of as catalyst poisons. The reasons for retardation of a reaction by such poisons most often reside in an adsorptive displacement of the reaction components from the electrode surface by adsorption of the foreign species. 

The Role of the Solvent in Polymer Adsorption Displacement and Solvency Effects... 

Thakkar, S., and M. Manes, Adsorptive Displacement Analysis of Many-Component Priority Pollutants on Activated Carbon. 2. Extension of Low Parts per Million (Based on Carbon), Environ. Sci. Technol., 22, 470-472 (1988). 

If at the adsorption of substances I and J on the same site the value of (AGfl°), does not differ much from that of (AGfl°)j, these values change equally when passing to any other surface site. In other words, the value of AG° for the reaction of adsorption displacement... 

We shall denote the equilibrium constant of adsorption displacement... 

Retention on these supports is adaquetely described by the adsorption displacement model. Nevertheless, the adsorption sites are delocalized due to the flexible moiety of the ligand, and secondary solvent effects play a significant role. The cyano phase behaves much like a deactivated silica toward nonpolar and moderately polar solutes and solvents. Cyano propyl columns appear to have basic tendencies in chloroform and acidic tendencies in methyl tertiobutyl ether (MTBE)... 

Gu, B., T. L. Mehlhorn, L. Liang, and J. F. McCarthy. 1996. Competitive adsorption, displacement, and transport of organic matter on iron oxide. II. Displacement and transport. Geochimica et Cosmochimica Acta 60 2977-2992. 

A special case of defoaming is observed when a soap solution (sodium oleate) is added to a foam, stabilised by saponin. It is know that addition of soap to a saponin solution leads to a decrease in foam volume and stability [e.g. 2]. Some saponin + soap mixtures do not produce a foam at all. It is not possible to explain foam inhibition in these systems with the adsorption displacement, since foam inhibition occurs when soap is added to saponin solution as well as when saponin is added to the soap solution. 

When polar hydrocarbons or typical diphilic antifoams (fatty alcohols and acids, ether, siloxanes, etc.) are used, the stability of foam films decreases for two reasons. The first one is related to the adsorption displacement of the surfactant from the antifoam and the second one to the considerable change in the surfactant monolayer at the organic phase interface caused by the transformation of the foam film into an asymmetric film. The adsorption at the organic/water interface strongly decreases compared to the adsorption at the water/air interface. 

Dekany, I. and Nagy, L. G. Immersional wetting and adsorption displacement on hydrophilic/hydrophobic surfaces.. Colloid Interface Sci. 147(1) 119—28, 1991. 

Surface dilatational rheology is a very sensitive technique to analyze the competitive adsorption/displacement of protein and LMWE emulsifier at the air-water interface (Patino et al., 2003). A common trend is that the surface dilatational modulus increases as the monolayer is compressed and is a maximum at the highest surface pressures, at the collapse point of the mixed film, and as the content of LMWE in the mixture increases. At higher TT, the collapsed protein residues displaced from the interface by LMWE molecules have important influence on the dilatational characteristics of the mixed films. The mechanical properties of the mixed films also demonstrate that, even at the highest tt, the LMWE is unable to displace completely protein molecules from the air-water interface. 

Figure 8 Schematic illustration of four different adsorption/displacement models proposed by Wahlgren and Amebrant [63] for protein and surfactant adsorption to solid surfaces. The three diagrams for each model show protein adsorption, surfactant addition, and state after rinsing. Figure A represents the case where surfactant binds to the protein and the protein-surfactant complex desorbs. Figure B represents protein displacement by the surfactant. Figure C represents reversible adsorption of the surfactant by the protein. Figure D represents reversible adsorption by the surfactant resulting in partial desorption of the protein. The figures relate to a hydrophilic surface at a hydrophobic surface the orientation of the surfactant molecules with respect to the surface will be different. (Reproduced from [63] with permission from Academic Press.)...

Sulfur exchange (and uptake) experiments are performed usually applying H2/H2S gas mixtures of different H2 H2S ratio. Comparison of H2/H2 S (with 90% content of the stable sulfur isotope ( S)) experiments with those of Ar/H2 S, indicatedthat the presence of H2 had no essential influence on the extent of S exchange, whereas the introduction of H2 S resulted in a sharp evolution of H2, indicating that H2S adsorption displaced H2 quickly. Consequently, different amounts of H2 at different H2 H2S ratio should not affect the S-exchange and uptake. The differences in results can be assigned to the differences in H2S pressure. 

The static adsorption capacity, static activity X, may be derived from the respective adsorption isotherm (see Chapter 1.4.4.2). A steep course of the isotherm in the log A /log Pi diagram gives a favorable adsorption. Additional adsorbent consumption has to be taken into account during design to consider adsorbent ageing, adsorbent damage, adsorption displacement etc. [4.28, 4.29, 4.34]. 

When adsorption displacement proceeds from Xi = 1 toward Xi = 0, the heat effects detected are of a reverse sign in the case of each isotherm. This means that the processes of displacement are reversible to a close approximation. A very Uttle irreversibility was detected only in the case of activated carbon Chem-viron, which is probably caused by incomplete displacement of methanol from the micropores by benzene. 

When alcohol-benzene mixtures are adsorbed on adsorbents with low surface energies, S-shaped excess isotherms are measured [17-19,32,33]. When changes in enthalpy accompanying the adsorption displacement process are examined in these systems, the integral exchange enthalpy isotherms usually do not increase monotonously but possess a backward section. After... 

HD Goff. Colloidal aspects of ice cream A review. Int Dairy J 7 363-373, 1997. JA De Feijter, J Benjamins, M Tamboer. Adsorption displacement of proteins by surfactants in oil-in-water emulsions. Colloids Surf 27 243-266, 1987. 

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