Reverse micelles interaction between

This self-organization in reverse micelles interacting through a sticky potential is actually general in extractant solutions for extractant concentrations typically between 0.2 and 1 M, namely for the concentration ranges usually used in industrial processes. 

The strong interactions between the water molecules also become obvious from NMR measurements by Tsujii et al..57) 13C-NMR experiments were used for determining the microviscosity of water in reversed micelles of dodecylammonium-propionate with 13C glycine cosolubilized. It was found that the apparent viscosity of the water-pool corresponds to the viscosity of a 78 % aqueous glycerol solution, obviously as a consequence of the extended network formation by strong hydrogen bonding. 

Dendrimers can also be prepared with an inverse relationship between their hydrophobic and hydrophilic constituents, i.e. with a hydrophobic periphery and a hydrophilic interior. They can then behave as reverse micelles and are able to concentrate polar molecules from solutions of nonpolar solvents. The shape of these molecules, when dissolved in a solvent that matches the hydrophobic nature of the periphery, is spherical with chain-ends extended towards the solvent. The interior may then collapse to a minimum volume, so that unfavourable interactions that might result from penetration by solvent molecules are minimized. 

It follows that in spite of the apolar coat surrounding water-containing AOT-reversed micelles and their dispersion in an apolar medium, some microscopic processes are able to establish intermicellar attractive interactions. These intermicellar interactions between AOT-reversed micelles increase with increasing temperature or the chain length of the hydrocarbon solvent molecule, thus leading to the enhancement of the clustering process [244-246], whereas they are reduced in the presence of inorganic salts [131]. 

By dynamic light scattering it was found that, in surfactant stabilized dispersions of nonaqueous polar solvents (glycerol, ethylene glycol, formamide) in iso-octane, the interactions between reversed micelles are more attractive than the ones observed in w/o microemulsions, Evidence of intermicellar clusters was obtained in all of these systems [262], Attractive intermicellar interactions become larger by increasing the urea concentration in water/AOT/ -hexane microemulsions at/ = 10 [263],... 

The ease of formation of hydrophobic ion pairs, and hence the rate acceleration, will be determined by the hydrophobic and electrostatic interactions between the anionic and cationic species. Lapinte and Viout (1974) found that the nucleophilic order OH- > CN > C6H50- in water was completely reversed in CTAB micelles hydrophobic phenoxide ion is activated better by the micelle. The micellar binding of phenols and phenoxides was determined by Bunton and Sepulveda (1979). Similarly, hydrophobic hydroxamates are activated much better than their hydrophilic counterparts. In the same vein, the extent of activation correlates approximately with the hydrophobic nature of aqueous aggregates as estimated by Amax of methyl orange (Table 7) and of picrate ion (Bougoin et al., 1975 Shinkai et al., 1978f Table 5). 

Effect of salt type and concentration The ionic strength of the aqueous solution in eontaet with a reverse micelle phase affects protein partitioning in a number of ways [18,23]. The first is through modification of electrostatic interactions between the protein surface and the surfaetant head groups by modifieation of the eleetrieal double layers adjacent to both the eharged inner mieelle wall and the protein surface. The second effect is to salt out the protein from the mieelle phase because of the inereased propensity of the ionie speeies to migrate to the micelle water pool, reduee the size of the reverse mieelles, and thus displace the protein. 

The ease that certain protein mixtures can be separated using reverse micelle extraction was clearly demonstrated by Goklen and Hatton [46], Goklen [31], and Jarudilokkul et al. [25], who investigated a series of binary and ternary protein mixtures. In two cases, they were able to quantitatively extract cytochrome c and lysozyme from a ternary mixture of these proteins with ribonuclease A. Woll and Hatton [24] investigated the separation of a mixture of ribonuclease A and concanavalin A, and showed that the system behaved ideally and that there was no interaction between the proteins. 

We first consider emulsion droplets submitted to attractive interactions of the order of ks T. Reversible flocculation may be simply produced by adding excess surfactant in the continuous phase of emulsions. As already mentioned in Chapter 2, micelles may induce an attractive depletion interaction between the dispersed droplets. For equal spheres of radius a at center-to-center separation r, the depletion... 

Rahaman and Hatton [152] developed a thermodynamic model for the prediction of the sizes of the protein filled and unfilled RMs as a function of system parameters such as ionic strength, protein charge, and size, Wq and protein concentration for both phase transfer and injection techniques. The important assumptions considered include (i) reverse micellar population is bidisperse, (ii) charge distribution is uniform, (iii) electrostatic interactions within a micelle and between a protein and micellar interface are represented by nonlinear Poisson-Boltzmann equation, (iv) the equilibrium micellar radii are assumed to be those that minimize the system free energy, and (v) water transferred between the two phases is too small to change chemical potential. 

Reverse micelles are well known to be spherical water in oil droplets stabilized by a monolayer of surfactant. The phase diagram of the surfactant sodium bis(2-ethylhexyl) sulfosuccinate, called Na(AOT), with water and isooctane shows a very large domain of water in oil droplets and often forms reverse micelles (3,23). The water pool diameter is related to the water content, w = [H20]/[ AOT], of the droplet by (23) D(nm) = 0.3w. From the existing domain of water in oil droplets in the phase diagram, the droplet diameters vary from 0.5 nm to 18 nm. Reverse micelles are dynamic (24-27) and attractive interactions between droplets take place. 

The intermicellar exchange process, governed by the attractive interactions between droplets, can be modified by changing the bulk solvent used to form reverse micellar solution (26). This is due to the discrete nature of solvent molecules and is attributed to the appearance of depletion forces between two micelles (the solvent is driven off between the two droplets) (26). When the droplets are in contact forming... 

Addition of Kryptofix 222 and Kronenether to reverse micellar system induces no changes in the droplet size and an increase in the droplet-droplet interactions. The complexation of cations Na of AOT led to a decrease in counterion binding, and consequently repulsive interactions between polar head groups of AOT surfactant are increasing. This could induce a more flexible interface of reverse micelles. 

Surfactant aggregation in an anhydrous, nonpolar medium differs in several important respects from aggregation in water. The most apparent of these differences is that the hydrophobic effect plays no role in the formation of reverse micelles. The amphipathic species are relatively passive in aqueous micellization, being squeezed out of solution by the water. In contrast, surfactant molecules play an active role in the formation of reverse micelles, which are held together by specific interactions between head groups in the micellar core. 

Chiarizia, R., Thiyagarajan, P., Jensen, M.P. et al. 2003. Third phase formation in TBP solvent extraction systems as a result of interaction between reverse micelles. In Leaching and Solution Purification, Vol. 1. Proc. Hydrometallurgy 2003 5th Int. Conf. in Honor of Prof. I. Ritchie. Young, C. A. et al. Eds. The Minerals, Metals and Materials Society, Warrendale, PA, pp. 917-928. 

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