Micellar swelling

One of the most common structures encountered in microemulsions consists of water or oil droplets dispersed in a continuous phase of oil or water, respectively. The type of dispersion results from the preferred curvature Co of the surfactant layer, which is by convention positive for oil-in-water (O/W) systems and negative for water-in-oil (W/O) systems. Co can be varied by adjusting the surfactant/cosurfactant ratio, which allows swelling of the droplets until a maximum is reached. When the systems become more concentrated, the micellar swelling is mostly limited by attractive interparticle interactions, as observed, for example, for microemulsions close to a critical point. 

Water, aqueous solutions and many other strongly hydrophilic substances can be solubilized within the micellar core [19,20], Water solubilization involves hydration of the surfactant headgroup accompanied by an increase in the head-group area, a micellar swelling, a marked increase in the surfactant aggregation number, and, at constant surfactant concentration, a decrease in the number density of reversed micelles [21], A representation of a spherical reverse micelle entrapping a polar solubilizate in the core is shown in Fig. 3. 

By swelling with aqueous electrolyte, cations (and, to lesser extent, also anions) penetrate together with water into the hydrophilic regions and form spherical electrolyte clusters with micellar morphology. The inner surface of clusters and channels is composed of a double layer of the immobilized —SO3 groups and the equivalent number of counterions, M+. Anions in the interior of the clusters are shielded from the —SOJ groups by hydrated cations and water molecules. On the other hand, anions are thus... 

In milk powders, the caseins are the principal water sorbants at low and intermediate values of aw. The water sorption characteristics of the caseins are influenced by their micellar state, their tendency towards self-association, their degree of phosphorylation and their ability to swell. Sorption isotherms for casein micelles and sodium caseinate (Figure 7.14) are generally sigmoidal. However, isotherms of sodium caseinate show a marked increase at aw between 0.75 and 0.95. This has been attributed to the... 

The surfactant, cetyltrimethylammonium bromide, was dissolved in water to obtain a clear solution, in which the first swelling agent (decane) was then added drop by drop with stirring. After ten minutes stirring at room temperature, the second swelling agent (TMB) was introduced. Sodium silicate was added to the obtained micellar solution and the pH value was adjusted with sulfuric acid. The pH value and surfactant/silicium molar ratio was fixed at 10 and 0.62 according to the protocol established previously for conventional MCM-41 synthesis... 

Incorporating jointly decane and 1,3,5-trimethylbenzene during the micellar solution preparation allows us to expand further the pore size, which can be adjusted up to 9.0 nm. Using only alkane [16] and in particular decane [17] as swelling agent the maximum pore size archived was 5.0 nm. 

From Table 1, it is evident, compared to the sample obtained without introduction of decane with the pore size of 2.6 nm, that the introduction of decane during the synthesis has a beneficial effect on the pore diameter. However the largest pore size is obtained if the swelling agent is added during the preparation of the micellar solution. In fact, if the decane is... 

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