Monomer role cosurfactant

In summary, these results show that the role of the monomer is twofold as a cosurfactant, it increases the flexibility and the fluidity of the interface, which favors the formation of a bicontinuous microemulsion. An an electrolyte, it induces the latter structure. These two conditions are imperative. Similar water-oil-surfactant (s) systems do not lead to bicontinuous microemulsions in the absence of monomers or salts (when the monomer is not itself an electrolyte). 

These AOT microemulsions are characterized by a high surfactant to monomer ratio, (2.5-3). If the amount of AOT is too low, the optically transparent microemulsions evolve towards turbid and unstable latexes during polymerization, due to a shift in the emulsion region of the phase diagram [55,56]. However, it should be noted that AM plays the role of a cosurfactant in these systems, owing to its surface-active properties, thus leading to an increase in the micellar stabilization capacities [48]. 

Monomers once again play the role of cosurfactant, considerably extending the region of the phase diagram in which microemulsions can exist (see Fig. 6.4). 

All these results should convince us that the monomer plays a crucial role in the phase diagrams of these systems. In fact, this role, more or less ignored by formulators until recently, is two-fold. As a cosurfactant, the monomer increases flexibility of the interfacial film. It can therefore deform more easily to produce a sponge structure. And as an electrolyte, the monomer reduces aqueous solubility of ethoxylated surfactants. It thereby favours their gradual transfer into the organic phase and the formation of a bicontinuous structure. This effect of salt in the formation of bicontinuous microemulsions is well known to the users of such systems. It is significant in this respect that the same systems without monomer or electrolyte (if the monomer is neutral) do not lead to bicontinuous structures. 

Sharma and Shah [46] reported that the surface tension of the SDS/alkyl alcohol aqueous solutions was minimum when the chain lengths of the surfactant and that of the alcohol were equal, e.g., for the SDS/CjzOH solutions. This was attributed to the tight packing of the molecules at the air-water interface. Patist et al. [47] reported similar results for SDS/alkyl trimethylammonium bromide/water systems. By the same token, C12 alkyl acrylates and methacrylate/SDS/water systems are expected to have a minimum surface tension and more solubilization of the monomer resulting in an increase in the one-phase region. The role of acrylates as cosurfactants has already been established in the case of hydroxy alkyl methacrylates [48]. 

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