Intermicellar processes

In connexion to the study of swelling phenomena and chemical reactions in cryptocrystalline macromolecular systems, the terms intramicellar and intermicellar processes were introduced by Katz and have become very popular. The former refers to processes occurring between the crystallites, the latter to occurrences inside them. They can be discriminated by X-ray examination. (See section 6b. 8, p. 577). 

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]. 

In principle, silica growth kinetics may be controlled by (1) slow release of monomer via alkoxide hydrolysis in the particle-free reverse micelles, (2) slow surface reaction of monomer addition to the growing particle, and (3) slow transport processes as determined by the dynamics of intermicellar mass transfer. There is strong experimental evidence to support the view that the rate of silica growth in the microemulsion environment is controlled by the rate of hydrolysis of TEOS (23,24,29). Silica growth kinetics can be analyzed in terms of the overall hydrolysis and condensation reactions ... 

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... 

This process has been used to make nanosized material by either chemical reduction of metallic ions or coprecipitation reactions. These various factors (water content, intermicellar potentials) control the size of the particles. 

The influence of the addition of cetyl trimethyl ammonium chloride, CTAC, to the reverse micellar solution affects the droplet size and micellar interactions, as demonstrated by the DQLS experiment (64). Addition of CTAC to micellar system at a given water content leaves the droplet size unchanged, whereas a decrease in the intermicellar attraction has been observed. This decrease is more important for high CTAC concentrations. This has been interpreted to steric repulsion induced by the long hydrocarbon tail of CTAC (C ft). Thus, the addition of this compound to CdS synthesis could modify the nucleation and/or growth process. The experiments were performed by solulization of CTAC in the micellar solution containing either sodium sulfide or Cd(AOT)2. 

ForCaCO, particles in W/O microemulsions of hexaethylene glycol dodecyl ether, however, the values of Nm/Np lie between 0.044 and 0.28, indicating that the particles form by the destruction of micelle-solubilizing aqueous Ca(OH)2 rather than by the intermicellar exchange process (5). In the case of the formation of CaCO-) particles in the Ca salt of Aerosol OT-cyclohexane system, as seen in Table 7.2.2, the particles... 

Solubilization of lipid digestion products in intestinal mixed micelles enhances their dissolution and dramatically increases the GI lumen-enterocyte concentration gradient that drives absorption by means of passive diffusion. Micelles, however, are not absorbed intact [8, 9], and lipids are thought to be absorbed from a monomolecular intermicellar phase in equilibrium with the intestinal micellar phase [10], The dissociation of monomolecular lipid from the micellar phase appears to be stimulated by the presence of an acidic microclimate associated with the enterocyte surface [11,12], In addition to passive diffusion, growing evidence suggests that active uptake processes mediated by transport systems located in the enterocyte membrane are also involved in the absorption of (in particular) fatty acids into the enterocyte [4],... 

Figure 17 shows that the particle diameter decreases with W when the concentration of reactant is very low (0.001 mol/L), conversely to Fig.8. The reason is that relatively fewer water cores will contain the minimum number of ions required to form a nucleus. As a result, the nucleation process is relatively larger. These ions will be incorporated into the already formed nuclei via intermicellar communication and will contribute to growth, leading to larger particles.

The consolidation mechanism of SPC compositions containing these additives can be considered as resulting from two processes decompression of silicon acid gel due to a decrease in the surface tension of intermicellar liquid and polymerization under the influence of acid solutions. 

Micelles are not frozen objects. They are in dynamic equilibrium with the free (nomnicellized) surfactant. Surfactants are constantly exchanged between micelles and the intermicellar solution (exchange process), and the residence time of a surfactant in a micelle is fmite. Besides, micelles have a finite lifetime. They constantly form and break up via two identified pathways by a series of stepwise entry/exit of one surfactant A at a time into/from a micelle (Reaction 1) or by a series of frag-mentation/coagulation reactions involving aggregates A, and Aj (Reaction... 

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