Polymeric surfactant phase diagram

Fig. 47. Phase diagram of the system water-polymeric surfactant (see Table 11,. No. 3)...

In addition to giving information about the shape and internal structure of colloidal aggregates, SANS studies can also be used profitably to determine the thickness and conformation of polymer layers adsorbed onto the surface of colloidal particles such as latex nanoparticles, and in some special cases, the surface of emulsion droplets. ° In such studies, the particles on which the polymer is adsorbed must generally be very accurately contrast matched to the solvent so as to allow information to be obtained only about the adsorbed layer. SANS studies have also been recently used in combination with differential scanning calorimetry and visual inspection of the solutions, to draw up a (simplified) partial phase diagram of the aggregation behavior of a polymeric surfactant in water.t ... 

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]. 

The phase diagrams of the ternary systems allow one to make a direct comparison between emulsion and microemulsion polymerization processes just by varying the surfactant concentration, as shown by Gan and coworkers [84,91,127]. Figure 8 represents the polymerization rate conversion curves for methyl methacrylate polymerization at different surfactant concentrations. 

Alexandridis et al. (2000) identified all the structures discussed above on a water/oil/PEO-PPO-PEO phase diagram. Because the solutions in many parts of the phase diagram are very viscous for these polymeric surfactants, further lowering of the temperature makes it very difficult to equilibrate the system. As a result, very often full temperature dependence is not reported, and has not been reported by Alexandridis et al. (2000). However, for these nonionics it is important to consider temperature dependence because of the changes it brings to the EO groups. Thus an additional effect of cloud point should also exist at low temperatures in this system. 

The SANS technique was further adopted to study the partitioning of monomer between microemulsion droplets and polymer particles for various monomers (ST, w-butyl methacrylate, -butyl methacrylate, and CeMA) (34). It was found that, during microemulsion polymerization, the partitioning of monomer is strongly dependent on the composition of microemulsion, especially on the distance to the phase boundary in the pseudo three-phase diagram of the surfactant/cosurfactant-oil-water system. For example, the monomer partitioning is linear in nature and the concentration of monomer in polymer particles is quite low if the initial microemulsion composition is far away from the phase boundary. In contrast, the monomer partitioning is essentially nonlinear and the... 

In contrast, the phase diagram of the polymeric surfactant shown in Fig. 5.15 displays three well-defined liquid crystal regions, namely lamellar (L j), hexagonal (Hi) and cubic (Vi). The two former phases are optically anisotropic and may therefore be easily identified by their characteristic textures. The narrow region of cubic phase, however, is optically isotropic and was identified by virtue of its high viscosity and shear birefringence. 

Fig. 5.15. Phase diagram of the polymeric surfactant-water system. Black region represents bicontinuous cubic phase, Vj.

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