Critical aggregation concentration formation

Fig. 22 Comparison of critical aggregate concentration, determined by excimer formation of covalently labeled polymer and micropolarity response of free pyrene...

The HMHECs used in these experiments provided good examples of an associative thickener, in that clear evidence of a critical aggregation concentration was seen from the dilute-solution behavior. Although some limited molecular aggregation may occur below this concentration, once this concentration is achieved, a three-dimensional network starts to form. This network formation leads to a significant enhancement of adsorption onto polymer latex particles from which the surfactant has been removed. The adsorption density is high for a cellulosic polymer of the equivalent molecular weight. 

A well-known feature of surfactant solutions is their ability to dissolve a variety of oil-soluble materials, e.g., hydrocarbons, esters, perfumes, dyes, and so on. This property is utilized in the compounding of many formulations, the process involving the dissolution of the solubihzate in the surfactant micelles. Formation of polymer/surfactant complexes is currently regarded as a depression of the critical aggregation concentration of the surfactant. According to this picture, superior solubilization in such systems can be anticipated... 

A series of cationic gemini surfactants, alkanediyl-ot,a)-bis[di(2-hydro-xylethyl) dodecylammonium] dibromide (abbreviated as 12-S-12 (OH), with s = 4, 6, 8 and 10 methylenes) have been synthesized, and their aggregation properties in aqueous solution have been studied by surface tension, calorimetry, H NMR, DLS, and TEM. Two critical aggregation concentrations are observed for these surfactants. These surfactants start to form dimers at concentrations well below their critical micelle concentrations (CMC). Above the CMC, these surfactants can form both micelles and vesicles spontaneously with a micelle-to-vesicle transition.The formation and characterization of catanionic vesicles by newly synthesized lysine- and... 

Excimer formation was also found to occur with the onset of aggregation. Figure 2.9 shows a plot of Ie/ m as a function of log polymer concentration for each polymer. The maxima of the curves occur at approximately the critical aggregation concentrations. Assuming that at the maxima of the curves there... 

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