Critical association concentration CAC

Mixed micelles, comprising both polymerized and free surfactants, are formed once the critical association concentration (CAC) of the free am-phiphiles is reached. The CAC is typically much smaller than the CMC for the formation of free micelles. As the fraction of unpolymerized surfactants within the mixed micelles grows, their structure approaches that of free micelles. 

Amphiphilic poly(ethylene glycol)-alkyl dextran ethers are emerging as vehicles in the oral delivery of poorly water soluble drugs [251,268,269]. They form polymer micelles of low critical association concentrations (CAC) and small micelle sizes in aqueous solution. Particulate delivery systems lead to an enhancement of the absorption efficiency and bioavailability of highly hpophihc drugs orally applied, and provide the drug with some level of pro-... 

Many techniques can be used for the determination of critical association concentrations (CACs), however, not all of them are sensitive enough to detect the onset of aggregation if this occm i at very low concentrations. Since the CACs of block copolymers are usually much lower than those of low molecular mass surfactants [54], we used pyrene as a fluorescent probe and calculated the effective CACs from the changes in the spectral characteristics of pyrene [55] as a function of surfactant concentration. If we represent the intensity of the emission spectra as a function of the block copolymer concentration, we directly obtain C4C, [56]. From the excitation spectra we obtain CACi by representing the ratio /340//335 vs. log C. 

Hydrophobically modified polymers can associate in aqueous media to form micelle-like structures above their critical association concentrations (CACs). The nanosized self-aggregates were prepared using modified natural polysaccharides such as pullulan, curdlan, and glycol chitosan. The modified polysaccharides provide excellent biocompatibility, biodegradability, low immunogenicity, and biological activities. 

We may interpret the concentration dependence of y in the presence of a polymer as follows. At a certain concentration, often termed the critical association concentration (CAC) and denoted T in Figure 20.1, there... 

As mentioned above, HMI is expected to show aggregation in very dilute solutions. This is illustrated in Figure 15.2, which shows the variation of the intensity of scattered light as a function of HMI concentration [9]. The results clearly show a rapid increase in light scattering intensity above a critical concentration, which is identified as the critical association concentration (CAC). The latter value is equal to 5 x 10 mol/dm, which is low and typical for graft copolymers that associate in very dilute solutions, as discussed above. 

Because the main driving force for surfactant self-association in polymer-surfactant mixed systems is the hydrophobic effect, the binding of surfactants to polyelectrolytes exhibits a similar dependence on the length of the alkyl chain as known for free micellization. Surfactants with longer hydrocarbon chains bind more strongly to polyions than those with shorter chains, and the binding starts a lower surfactant concentrations. In this context, a convenient parameter to characterize polyelectrolyte-surfactant systems is the critical aggregation concentration, cac, which is a counterpart of the well-known critical micellization concentration, cmc, but applies to solutions of surfactants in the presence of a polymer. It is defined as the... 

In a system of fixed polymer concentration and varying surfactant concentrations, two critical concentrations appear, denoted Ti and T2- Ti represents the concentration at which interaction between the surfactant and polymer first occurs. This is sometimes termed the critical aggregation concentration (CAC), i.e. the onset of association of surfactant to the polymer. Because of this there is no further... 

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