Polarization energy ionic

Most studies of micellar systems have been carried out on synthetic surfactants where the polar or ionic head group may be cationic, e.g. an ammonium or pyridinium ion, anionic, e.g. a carboxylate, sulfate or sulfonate ion, non-ionic, e.g. hydroxy-compound, or zwitterionic, e.g. an amine oxide or a carboxylate or sulfonate betaine. Surfactants are often given trivial or trade names, and abbreviations based on either trivial or systematic names are freely used (Fendler and Fendler, 1975). Many commercial surfactants are mixtures so that purity can be a major problem. In addition, some surfactants, e.g. monoalkyl sulfates, decompose slowly in aqueous solution. Some examples of surfactants are given in Table 1, together with values of the critical micelle concentration, cmc. This is the surfactant concentration at the onset of micellization (Mukerjee and Mysels, 1970) and can therefore be taken to be the maximum concentration of monomeric surfactant in a solution (Menger and Portnoy, 1967). Its value is related to the change of free energy on micellization (Fendler and Fendler, 1975 Lindman and Wennerstrom, 1980). 

The mechanisms of adsorption of organic solutes—including hydro-phobic, polar, and ionic species—onto surfaces have been summarized previously (2 5). Assuming that the various adsorptive mechanisms act independently, the free energy of adsorption (AGa[Pg.192]

Among three-dimensional framework hosts forming intercalation compounds, zeolites (see Section 1.5) have attracted considerable attention because of their technical importance (Derouane, 1982 Dyer, 1984). Intracrystalline voids in anhydrous zeolites provide a strongly polar environment that can be filled with polar or ionic species to increase the crystal energy. Treatment of zeolites (e.g. Na-Y zeolite) with vapours of sodium results in the formation of a red product consisting of Na " intercalated into the zeolite cavities (Thomas, 1983). The locations of these clusters inside the zeolites are not yet known, but they seem to be buried within the rather inaccessible cavities inside zeolites, with the result that ordinary solvents do not reach them. Such intercalation of ionic species in zeolites may have implications in nuclear-waste treatment and storage. 

Polarization interactions for atoms and small molecules or functional groups are much weaker than the other interactions listed above. For example, in vacuum the attractive energy between two methyl groups is only about 0.15 kcal/mol (0.6 kJ/mol) at a separation of 0.4 nm. However, polarization interactions are additive, so that for large bodies with many individual polarization interactions (e.g., a protein binding a large substrate molecule) the overall contribution may be 10 to 20 kcal/mol (40-80 kJ/mol). Furthermore, these interactions will be present for both nonpolar and polar (even ionic) groups. 

As the square of the charge, the dielectric constant, and the ionic radius must all be positive, work must be expended to charge the sphere, but the work is less for higher exterior dielectric constants, as expected. Recalling that the polarization energy is the difference in the required work in the gas phase and solution, we may write... 

A role of polarization energy is also implicit in the AEe sequence K-L < Ba-L < La-L. K+ and Ba2+ have almost the same ionic radii, but the polarizing power of Ba2+ greatly exceeds that of K+ and that of La3+ similarly exceeds that of Ba2+. Accordingly the polarization component of bonding energy of Kr molecules adjacent to the cations would decrease in the order La3+ > Ba2+ > K+, in the observed sequence for AEe. 

COMPARISON OF FREE ENERGIES OF TRANSFER (ON THE MOLAR SCALE) FROM METHANOL TO WATER OF TRANSITION STATES WITH SOME NON-POLAR AND IONIC... 

The third general model (cf Pearson and Gray (13), Klopman (14), and Ferreira (15)) considers a partial ionic bond. In this model both the Van der Waals and the polarization energies are discarded in an attempt to see... 

One approach (4) is to calculate, for a certain zeolite structure, the Madelung and polarization energies for fixed lattice positions. The heat of formation due to ionic bonding is calculated both for the zeolitic aluminosilicate with varying amount of aluminum and... 

It should be noted that the electrostatic energy U can be estimated directly (as discussed for site-preference energies) or obtained from the observed activation energy for d-electron conduction, to which is added the ionic polarization energy. The parameter by is more difficult to estimate. It is proportional to the orbital overlap and so must increase exponentially with decreasing cation-cation separation. 

Non-additive terms effects of polarization in the potential function. Polarization effects induced by the ionic presence on the ion-molecule system have been investigated. We use the expression by Lybrand and Kollman24 that includes in the potential function a self-consistent field (SCF) polarization energy Upoi based on classical electrostatics, given by ... 

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