Pure surfactant micelle

Type 6 - Pure surfactant micelles associate with the polymer molecule in such a way that the polymer segments partially penetrate and wrap around the polar head group region of the surfactant micelles. A single polymer molecule can associate in this manner with one or more surfactant micelles depending on the polymer and micellar properties. 

The clusters consisting of surfactant molecules only are indicated by // = 0, so that we have 1 = Zi,0 in the distribution function (7.95). There are junctions of multiplicity k = li only in such pure surfactant micelles. We then have jk= for fc = /1, otherwise jk = 0. The distribution function becomes... 

The formation of mixed micelles in surfactant solutions which contain two or more surfactant components can be significantly affected by the structures of the surfactants involved. The observed critical micelle concentration (cmc) is often significantly lower than would be expected based on the erne s of the pure surfactants. This clearly demonstrates that interactions between different surfactant components in the mixed micelles are taking place. 

Of the possible types of measurements, heats of micellar mixing obtained from the mixing of pure surfactant solutions are perhaps of the greatest interest. Also of interest is the titration (dilution) of mixed micellar solutions to obtain mixed erne s. While calorimetric measurements have been applied in studies of pure surfactants (6,7) and their interaction with polymers ( ), to our knowledge, applications of calorimetry to problems of nonideal mixed micellization have not been previously reported in the literature. 

Below the CMC, the surfactant mixing in monolayers composed of similarly structured surfactants approximately obeys ideal solution theory. This means that the total surfactant concentration required to attain a specified surface tension for a mixture is intermediate between those concentrations for the pure surfactants involved. For mixtures of ionic/nonionic or anionic/cationic surfactants, below the CMC, the surfactant mixing in the monolayer exhibits negative deviation from ideality (i.e., the surfactant concentration required to attain a specified surface tension is less than that predicted from ideal solution theory). The same guidelines already discussed to select surfactant mixtures which have low monomer concentrations when micelles are present would also apply to the selection of surfactants which would reduce surface tension below the CMC. 

Nishikido (21) has done a systematic study o-f mixed sur-factant solubilization. In that study, solubilization in mixed systems was compared to that predicted by application o-f a linear mixing rule to the solubilizations in the pure surfactant component micelles. For example, in this "ideal case, a micelle composed of a 50/50 molar mixture of two surfactants would have a solubilization capacity which is an average of that of the two pure surfactants involved. A system showing negative deviation from ideality would have less solubilization than this ideal system a system having positive deviation from ideality would have more. 

In the case of system (ii), 6ED and NF are not miscible at concentrations below the CMC of both pure surfactants above the both pure CMC values, the mixed micelles are formed. 

Above the critical micelle concentration (C ) in a pure surfactant solution the chemical potential of the monomer is given by... 

Non-ideal solution theory is used to calculate the value of a parameter, S, that measures the interaction between two surfactants in mixed monolayer or mixed micelle formation. The value of this parameter, together with the values of relevant properties of the individual, pure surfactants, determines whether synergism will exist in a mixture of two surfactants in aqueous solution. 

Synergism in mixed micelle formation. Synergism in this respect is present when the critical micelle concentration of any mixture is lower than that of either pure surfactant. This is illustrated in Figure 2. 

None of these methods have been widely adopted because of their relative complexity or because they are not generally applicable to any arbitrary surfactant system. As examples, the surface tension method (4) relies on the pure surfactants having substantially different plateau surface tensions the ultrafi1tration method (1,) requires the micelles of the pure surfactants involved to have approximately the same size and the... 

The process utilizing supramolecular organization involves pore expansion in silicas. A schematic view of such micelles built from the pure surfactant and those involving in addition n-alkane is shown in Figure 4.9. Another example of pore creation provides a cross-linking polymerization of monomers within the surfactant bilayer [30]. As a result vesicle-templated hollow spheres are created. Dendrimers like that shown in Figure 4.10 exhibit some similarity to micellar structures and can host smaller molecules inside themselves [2c]. Divers functionalized dendrimers that are thought to present numerous prospective applications will be presented in Section 7.6. 

The situation is complicated by the fact that the cmc value determined in the pure surfactant solution generally differs from that fomid in the presence of biopolymer. This is mainly because the surfactant-biopolymer interactions can shift the equilibrium between free surfactant molecules and their micelles, leading to a change in the effective cmc of surfactant molecules in the biopolymer system (Kelley and McClements, 2003 McClements, 2000 Thongngam and McClements, 2005). 

In this equation the standard state corresponds to the state that results from letting fw - 1 and xw - 1, in which case = n°s w. Letting/ - 1 is equivalent to saying that the surfactant behaves ideally, and letting xw - 1 is equivalent to having pure surfactant possessing the kind of interactions it has when surrounded by water. Physically, this corresponds to an infinitely dilute solution of surfactant in water. Using the primed symbol to represent the chemical potential of surfactant in micelles per mole of micelles, we write... 

Table I and Figures 1-4 contain a wealth of information about the solubilization of benzene in aqueous surfactant micelles. Plots of K vs. Xg exhibit shallow minima in the case of the SDS solutions, and rather more pronounced minima for the CPC solutions. The plots of Tg vs. Xg show corresponding maxima, reflecting the fact that K and Yg are related reciprocally by K l/(TBcB ), where cB° is the monomer concentration of benzene in the aqueous phase at saturation. (The minimum in K and the maximum in Yg for the CPC solutions, shown in Figure 1, are not quite reached at the benzene concentrations attainable with the automated vapor pressure apparatus. The automated apparatus is restricted to operating at partial pressures less than about 70% of the vapor pressure of pure liquid benzene. However, the manual apparatus can be used for measurements almost to saturation, and results obtained with this apparatus show extrema in K and Yg at approximately X = 0.55.)...

Surfactant surface activity is most completely presented in the form of the Gibbs adsorption isotherm, the plot of solution surface tension versus the logarithm of surfactant concentration. For many pure surfactants, the critical micelle concentration (CMC) defines the limit above which surface tension does not change with concentration, because at this stage, the surface is saturated with surfactant molecules. The CMC is a measure of surfactant efficiency, and the surface tension at or above the CMC (the low-surface-tension plateau) is an index of surfactant effectiveness (Table XIII). A surfactant concentration of 1% was chosen where possible from these various dissimilar studies to ensure a surface tension value above the CMC. Surfactants with hydrophobes based on methylsiloxanes can achieve a low surface tension plateau for aqueous solutions of —21-22 mN/m. There is ample confirmation of this fact in the literature (86, 87). 

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