Nonpolar Organophiles

The migration capability of these components depends on the mobility of their organic solvents. As mentioned earlier, they may be subdivided into two groups, those mobile relative to rocks and those immobile. 

However, coefficient describes not mobility proper but only the distribution of organic component between mobile ground water and organic matter. Let us assume that a component i is distributed only between ground water and the rock, i.e., a and ain equation (2.334) are equal to 0 and instead of coefficient. is used coefficient . Then, according to equations (2.327) and (2.336) 

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Organophilic membranes with a preferential permeation of nonpolar compounds are used for the removal of volatile organic components from aqueous and gas streams. 

Activated carbon is by far the most widely used adsorbent. It is available in a wide range of different forms that differ mainly in pore size and pore size distribution. The carbon surface is essentially nonpolar although some polarity can be imparted by surface oxidation or other pre-treatments. It is widely used for removal of low concentrations of organics, either from aqueous streams (for example, decolorization of sugar or water treatment) or from vapor streams (for example, in range hoods and other pollution-control devices). Crystalline silica adsorbents such as silicalite are also organophilic but are substantially more expensive than activated carbon so their application is generally limited to situations where, for some reason, the use of carbon is not appropriate. 

The layered silicate nanoparticles are usually hydrophilic and their interactions with nonpolar polymers are not favorable. Thus, whereas hydrophilic polymers are likely to intercalate within Na-activated montmorillonite clays [24-29], hydrophobic polymers can lead to intercalated [23,30-32] or exfoliated [33] structures only with organophilized clays, i.e., with materials where the hydrated Na+ within the galleries has been replaced by proper cationic surfactants (e.g., alkylammonium) by a cation exchange reaction. The thermodynamics of intercalation or exfoliation have been discussed [34-37] in terms of both enthalpic and entropic contributions to the free energy. It has been recognized that the entropy loss because of chain confinement is compensated by the entropy gain associated with the increased conformational freedom of the surfactant tails as the interlayer distance increases with polymer intercalation [34,38], whereas the favorable enthalpic interactions are extremely critical in determining the nanocomposite structure [39]. 

The surface of carbon is essentially nonpolar although a slight polarity may arise from surface oxidation. As a result, carbon adsorbents tend to be hydrophobic and organophilic. They are therefore widely used for the adsorption of organics in decolorizing sugar, water purification, and. solvent recovery systems as well as for the adsorption of gasoline vapors in automobiles and as... 

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