Salt partition

Figure 11.8 Formation of ordered nanoparticles of metal from diblock copolymer micelles, (a) Diblock copolymer (b) metal salt partition to centres of the polymer micelles (c) deposition of micelles at a surface (d) micelle removal and reduction of oxide to metal, (e) AFM image of carbon nanotubes and cobalt catalyst nanoparticles after growth (height scale, 5 nm scan size, lxl pm). [Part (e) reproduced from Ref. 47].

It is the hyperbolic relations (Ag )(Br ) = K and (M )(Y ) = (M+)(Y)/KZ that provides t e basic analogy be Seen the two kinds of systems. In the latter, K is the ionic salt partition coefficient relating membrane and bathing solution activities at an equilibrium interface. The latter form can also be derived for insoluble salt membranes. However the salt activities (super bar quantities) are constant and so are hidden in the value of the solubility product... 

The solvent effect on extraction constants is a combination of the influence on salt partition and association. Both processes are influenced by the polarity of the solvent [97]. The Kirkwood function describes the relation between polarity, , and extraction constant a more polar membrane solvent promotes extraction. In general, polar solvents favor salt partition, but the tendency toward complexation diminishes. Since the overall effect of solvent polarity on the extraction is positive, the polarity appears to affect the partition coefficient to a higher degree. 

Recovery of Proteins from Polyethylene Glycol-Water Solution by Salt Partition... 

PEG-water solution, 99f protein recovery by salt partition, 107... 

IV. SALT-PARTITIONING PROCESSES A. Water-Immiscible Solvents... 

As covered in comprehensive texts [2,3], early efforts in the study of salt partitioning by pure solvents were directed toward understanding the basic equilibria involved and the chemical factors influencing partitioning behavior. Figure 3 essentially encapsulates that early work. For the high-dielectric solvents, such as nitrobenzene or nitromethane, it was readily established that solvent-phase salts of the alkali metal cations with various... 

Figure 4 Large anions frequently employed as counterions in salt partitioning systems.

Figure 5 Dicarbollide derivatives used as anions in salt partitioning and cation exchange. The numbering scheme was taken from [210]. Formulas of the anions and names of the bridging groups were taken from [201] except for -phenylcne, the exact isomeric form of the bridging groups could not be determined from this reference or references cited therein. The structure of the unsubstituted anion DCC I is correct as shown when a bridging group is present, the carbon atoms in the hemispheres are constrained to the same side of the molecule.

A complete treatment of the analysis of equilibria in the many salt-partitioning systems that have been studied is beyond the present scope of this chapter, but an examination of some simple equilibrium systems will serve the purpose of revealing some of the salient features. We treat here simple salt partitioning in the three-component system water-solvent-salt. The equilibrium constant corresponding to Eq. (33) may be defined as... 

As mentioned above, ion pairing in the organic phase complicates the equilibrium analysis, but it also adds information on interactions that involve the cation and that may influence extraction selectivity. Continuing the discussion of salt partitioning in three-component systems, the expression for the salt partitioning equilibrium constant for an associated system [Eq. (34) is... 

D. Competitive Salt-Partitioning and Cation-Exchange Equilibria... 

To describe the selectivity of salt partitioning, many authors find it expedient to formally take the difference between Eqs. (42) and (33) to obtain the hypothetical exchange reaction [233] ... 

Whereas salt partitioning depends equally on the natures of the cation and the anion, the exchange process has no formal dependence on the anion and describes only the cation selectivity. By studying Eqs. (33) and (42) separately, we can infer the exchange given by Eq. (43). If we label the exchange constant Xs-. n-m, it may readily be seen that Xs. n-m = Xs (NX)/X,(MX). 

---