Micelles, micelle clustering

Beckman et al. observed an effect of the secondary microemulsion structure on the molecular weight and yield of the polymer. Under conditions where extensive micelle-micelle clustering occurred, at lower fluid density the molecular weight of the polymer was as much as two times higher. Thus, the density of the supercritical phase could be used to control the polymer morphology. Beckman and Smith also completed an extensive study [74] of the effect that acrylamide, surfactant, and water concentrations as well as the pressure and temperature had on the phase stability of the microemulsions. The phase behavior of these systems depends on the choice of operating parameters, and this behavior can be exploited to optimize the properties of the polymer. 

Systematic variation in the water temperature, (WW), will produce a profile reflecting this influence. Vary the / b(WW) and J(WW) values in Example 5.3 to simulate different water temperatures. Run the dynamics for these different water temperatures to observe its influence. Note whether this is a linear or nonlinear effect on the cluster size. The structures formed may be quantified by recording the average micelle cluster size. The typical pattern looks like the examples in Figure 5.5. 

Effectiveness of a crude oil demulsifier is correlated with the lowering of shear viscosity and dynamic tension gradient of the oil-water interface. Using the pulsed drop technique, the interfacial dilational modulii with different demulsifiers have been measured. The interfacial tension relaxation occurs faster with an effective demulsifier. Electron spin resonance with labeled demulsifiers indicate that the demulsifiers form reverse micelle like clusters in bulk oil. The slow unclustering of the demulsifier at the interface appears to be the rate determining step in the tension relaxation process. 

Fig.5 Cryo-TEM pictures of metallosupramolecular PS2o-[Ru]-PEC>7o (a) and covalent PS22-PEO70 (b) aqueous micelles. Arrows in a indicate isolated micelle and cluster of micelles. Reprinted with permission from [54]. Copyright (2004) Springer... 

When soap is dissolved in water, micelles are formed. These micelles are clusters of soap molecules... 

The rate of aggregation of fully renneted micelles is very sensitive to temperature. At room temperature it is appreciably less than the diffusional collision rate, which led Payens (1977) to consider the possibility that only a fraction of the surface is reactive (so-called hot spots). The idea of hot spots is consistent with the low fractal dimension of micelle clusters formed during renneting and leads to only a proportion of all encounters between fully renneted micelles being successful. In effect, a statistical prefactor is included in the reaction kernel to reduce the diffusion rate to a level comparable with experiment. However, Payens developed the idea of hot spots only within his theory of the aggregation of fully renneted micelles. 

Another important parameter that has to be deeply considered is the pH. It is well known the role of pH on silica chemistry it affects dissolution and polymerization rate, gel or precipitate formation and the textural properties of the final silica (11). Also for surfactant micelle or cluster templated syntheses of silica-aluminas, the effect of pH on porosity remains relevant and it is strongly influenced by the kind of material and by the synthesis route selected for its preparation. 

The most reasonable explanation for the increase in apparent hydrodynamic diameter measured by DLS is the enhanced micelle-micelle interactions as the boundary of a two-phase system is approached (i.e., the pressure is lowered). Figure 4 illustrates this concept of micelle-micelle interactions, which is manifested as aggregation (or clustering) of the reverse micelle or microemulsion droplets. Since the solvent environment is essentially unchanged by this "macromolecular aggregation" (Ui) we exclude the possibility of (other than transitory) micelle-micelle coalescence to form stable, larger micelles. The micelles may coalesce briefly to form transitional species (which might be a "dumbbell" or more cylindrical structures), in which the water cores collide and intermix. 

Clearly, much work remains to be done to fully explain the effects of continuous-phase density and the extent of micelle clustering, on both the rate of polymerization and the molecular weight of the polymer formed via this process. 

Micelle A cluster of a large number of soap or detergent molecules or ions, assembled with their hydrophobic tails directed toward the center and their hydrophilic heads directed outward. 

Each ion moves as an independent entity - but see discussion below of ion pairing and micelle clustering. 

Micelle clusters in equilibrium with free ions... 

A novel amine coupling method has been developed by Biacore in which an acidic protein is carried by a positively charged micelle (a cluster of oriented surfactant molecules). The micelle-protein complex carries a net positive charge at neutral pH, and is therefore attracted to the sensor surface (Fig. 14). 

A pearl necklace model in which the polypeptide chain forms the string of the necklace and the surfactant molecules form micelle-like clusters along the polypeptide chain, which passes through the micellar clusters in a a-helical conformation. In contrast to the rod-like particle model, this model assumes that the polypeptide chain is flexible. 

There has been very little work completed in reverse micelles. This may be due to the increased complexity of these systems, where probe migration and micelle clustering occurs on time scales similar to triplet decay. In addition, litde work has been carried out in vesicles or liposomes. With the advent of diffuse reflectance laser flash photolysis, the turbid solutions observed for large vesicles no longer represent a stumbling block [196-198]. Thus, we believe that, in the future, much more work will be available in vesicular systems that will be able to complement the studies already completed in micelles. 

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