Adsorption onto surfaces

In the above description of phenomena occurring when surfactants are put into solution, we omitted another thermodynamically allowed way for isolated molecules to escape contact with water. This is adsorption onto a surface or interface. 

Although this adsorption concerns only a tiny proportion of the molecules (see Fig. 4.5), it has a significant effect on the properties of amphiphilic solutions. By reducing the surface tension 7, it favours wetting (cf. Chap. 1) and foaming properties. This explains the term surface active agent or surfactant. 

Considering now that the surface tension is also an energy per unit area, we see that it measures the energy required to increase the surface area by one unit. If there is a surface pressure, this must reduce that energy. The surface pressure is equal to the difference in surface tensions on either side of the barrier. 

A simple model due to Langmuir gives this surface pressure and explains the role of the molecular parameters. It assumes that, at the gas/solution interface, at any time, a flux n of adsorbing molecules balances a flux U2 of desorbing molecules. Then n = k Cs, where Cg is the concentration in solution and ki a constant. The expression proposed for ri2 is 

Applying the 2-dimensional perfect gas law in conditions where 5 is small, we obtain 

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We suggest that the rapid process corresponds to hole-filling and/or adsorption onto surfaces, and that the slow process, which follows first-order behavior, corresponds to swelling of the coal extract. Extrapolation of the linear portion of the curves shown in Figures 10 and 11 to time zero should yield the total uptake of benzene attributed to swelling. The results of this analysis are summarized in Table IV, where the total benzene uptake, M , and the uptake attributed to the hole-filling/adsorption and the swelling processes, and M., are shown. 

Adsorption onto Particles. The Gibbs Adsorption law relates how adsorption onto surfaces affects interfacial tension, dy = - RTfd In c. where y = intcrfacial or surface tension, in N/m (I N/m = 1000 dyn/cm) R = gas constant T = absolute temperature T = interfacial or surface concentration, m mol/unil area (i.c.. adsorption) and i = dimensionless concentration (d In r- = t/r/r, thus units cancel). 

The increase in the amount of copper and decrease in the amount of zinc removed by activated sludge, as the residence time is increased, can be explained by transport processes, adsorption onto surfaces orthe possible competitionbetween copper and zinc ions in binding to available sites on the enzymes. It may be that the interaction between copper and biomass increases as the residence time increases eventually leading to an increase in the amount of copper taken up by activated sludge. As a result, the affinity of zinc for the... 

Our main focus for this review is to briefly and critically describe some of the defluoridation techniques as a means of getting a basis to support the adsorption technique, to evaluate the defluoridation adsorbents now being utilized and those novel defluoridation adsorbents reported in literature over the last two decades, with special reference to drinking water. Emphasis is laid toward the adsorbents availability, fluoride sorption capacity and where applicable their kinetic adsorption characteristics and column performances are reported. Detailed characteristics of fluoride adsorption onto surface-tailored zeolite are provided. In addition, various adsorber configurations are reexamined and challenges to and prospects for their application to less developed countries (LDCs) are discussed. 

Characteristics of fluoride adsorption onto surface-tailored low-silica zeolite... 

Measurement of the post-application residential exposure is, in many ways, more complicated than the agricultural re-entry since there may be multiple sources and routes of exposure, varying amounts of time spent in contact with these sources and a much wider age and health range in the exposed population (USEPA, 1991, 1999a). Chemicals such as pesticides that are released into or otherwise enter the residential enviromnent tend to partition into various compartments, either through direct dispersion in indoor air or through adsorption onto surfaces that serve as sinks from which material can subsequently be released into the air (Ross et al., 1990, 1991). A detailed discussion of the measurement of pesticides in the residential enviromnent is presented in Chapter 3. 

Adsorption. Monomeric silica can be removed from solution by adsorption onto surfaces of sesquioxide minerals (e.g., AljOa, FejOa) through pH-dependent reactions that apparently involve hydrogen bonding (see Jones and Handreck, 1967, and references therein) such reactions, especially with AI2O3, seem to exert a major control over the concentration of dissolved silica in soil solutions. 

Other materials have also been studied for their ability to reduce protein adsorption onto surfaces. Because many cell membranes are based on phospholipids, polymers containing phospholipid-type head groups have been utilized for this purpose. Poly(2-methacroylethyl phosphoryl choline) could be plasma deposited onto silicone rubber and the adhesion of albumin reduced by factors of up to 80 (Fig. 

Los ses ff dissolyed humic substances from the water column occur via adsorption onto surfaces of minerals and by cleavage upon exposure to UV radiation or ozone. Cleavage of humic molecules seems to be an important step in the decomposition of humic substances by microbes. Easily degradable substrates in the DOC pool (glucose, lactate, etc.) appear to stimulate microbial degradation of humic substances, either by a priming effect of an easily degradable substrate or by bacterial cometabolism. These... 

Adsorption onto surfaces such as suspended particulates, and carbonate or hydrous metal oxide precipitation. 

Analysis of binding data depends on the selection of a model. Since the binding is likely to be nonspecific, sharing also the feature of a ligand binding to a lattice, the models developed for adsorption onto surfaces or lines... 

Immobilization by adsorption onto surfaces such as activated carbon or an ion exchange resin gives a reversible and relatively weak bond, but this can be sufficient to increase the retention time in a flow system to acceptable levels. Recall Section... 

One possible objection to the comparison of protein adsorption on flat surfaces with platelet adhesion and activation in polymer-coated bead columns is raised by the work of Vroman et al. (28) who showed that protein adsorption onto surfaces from plasma in narrow... 

Of particular interest is the case of surfactant adsorption onto surfaces of opposite charge, in which a complex relationship between surfactant concentration and wetting is often encountered (Fig. 17.13). At low surfactant concen-... 

Adsorption onto surface and flux from position 0o,surf to 9q at the pore entrance via surface diffusion (f2.J). 

Infrared techniques can also be used to study protein adsorption onto surfaces. For example, a flow-through ATR cell can be used ex vivo with flowing blood. 

Aggregation Denaturation Adsorption onto surfaces Precipitation Chemical degradation can be caused by ... 

Protein adsorption onto surfaces is fundamental for the development of low-fouling surfaces, protein immobilization, and protein separations. Shordy after the implantation of materials into the body, proteins adhere to the device s surfaces. The adsorbed proteins act as an intermediary... 

As we know, protein adsorption is very important in engineer biosurfaces, such as nanobiointerface (Andre et al, 2009). Protein adsorption onto surfaces is fundamental for the development of nonfoubng surfaces... 

Traditionally, adsorption onto surfaces is described by isotherm equations tiat represent the isotherm with a few fitted parameters. These approaches although widely used have provided limited insight or predictive power. By contrast molecular based methods including molecular simulation and density functional methods offer both insist and accurate prediction, albeit for idealised models. . Initially, density functional theory (DFT) simulations were widely used [2,3] due to their speed. The trade off was that the adsorbate model was... 

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