Micelle form factor

SEES with oil leads to the transition from lamellar morphology to micellar morphology [15]. This transformation is reflected in the above images of pure SEES and its SEES/oil = 60 40 composition. The loading leads to an increase of the structural factor from 21 to 53 nm. Therefore, the incorporation of oil to ethylene-butylene blocks induced larger separation of micelles formed predominantly by styrene blocks. 

Another relatively new lipophilicity scale proposed for use in ADME studies is based on MEKC [106]. A further variant is called BMC and uses mobile phases of Brij35 [polyoxyethylene(23)lauryl ether] [129]. Similarly, the retention factors of 16 P-blockers obtained with micellar chromatography with sodium dodecyl sulfate as micelle-forming agent correlates well with permeability coefficients in Caco-2 monolayers and apparent permeability coefficients in rat intestinal segments [130]. 

Figure 3 Example of SANS curves at two times of the reaction. The lines are calculations of the form factor. (A) prior to TEOS addition, the micelles are well described by core-shell spheres, with an external radius of 7.1 ran. ( ) 15 minutes after the beginning of the reaction, the micelles can be viewed as cylinders of length 50 nm and radius 6.9 nm.

Fig. 4.27 SAXS intensity as a function of wavevector for a PS-P1 diblock (Mw = 60 kg mol-1, 17wt% PS) (points) in dibutyl phthalate with a polymer volume fraction

A typical spherical micelle contains 30-100 surfactants and has diameter of 3-6 nm. Micelles form because of two competing factors transfer of hydrocarbon chains out of water into an oil-like interior and repulsion between the head groups. 

The micelles formed in the non-polar solvents would seem in general to be relatively small, the aggregation number being of the order of 4 to 30. When the micelles are nearly spherical, as they seem to be at low concentrations, the low aggregation numbers are due to steric factors. The space in a spherical soft-core micelle permits only the accommodation of a limited number of polar groups this also applies to the number of bulky hydrocarbon groups in the outer parts of the micelle (Eicke, 1980 Ekwall, 1972 Kertes and Gutman, 1976 Rounds, 1976). 

Examination of equations 5, 6, and 7 reveals that retention can be controlled by variation of the surfactant micelle concentration, variation of pH (for ionizable species), and by manipulation of the solute-micelle binding constant (K. ) which, in turn can be influenced by additives (salt, alcohol referto data on DDT, Table VI) or the type (charge and hydrophobicity) of micelle-forming surfactant employed (refer to data in Table VII for 1-pentanol). Table VIII summarizes some of the factors that influence retention for surfactant-containing mobile phases and compares the effect of changes in these factors upon the retention behavior observed in both micellar liquid and ion-pair chromatography (81). 

FIG. 3 Comparison of theoretical form factors with experimental SAXS data at a water-to-EO molar ratio of micelles at 2.6. / g is the radius of gyration. (Reprinted with permission from the paper entitled Water-induced micellar structures of block copoly(oxyethylcne-oxypropylene-oxyethylenc) in o-xylene, by G. Wu, Z. Zhou, and B. Chu. J. Polym. Sci. Part B Polymer Physics. / 2045. Copyright 199.1 John Wiley Sons, Inc. ... 

The functionalization of the reverse micelles will create a novel application in bioseparation processes in the analytical and medical sciences. It is therefore important to reveal the recognition mechanism of proteins at the liquid-liquid interface in reversed micellar solutions. DNA is also successfully extracted in a few hours by reversed micelles formed by cationic surfactants in isooctane. The driving force of the DNA transfer is the electrostatic interaction between the cationic surfactants and the negatively charged DNA. Another important factor is the hydrophobicity of the cationic surfactants. Doublechain type cationic surfactants are found to be one of the best surfactants ensuring the efficient extraction of DNA. These results have shown that reverse micellar solutions will become a useful tool not only for protein separation, but also for DNA separation. 

In contrast to reaction (5-158), addition of micelle-forming surfactants can also slow down chemical reactions. For example, the spontaneous hydrolysis of phenyl chloroformate at 25 °C according to Eq. (5-158a) is retarded by a factor of ca. 16 on addition of sodium dodecylsulfate (SDS) above the one. Below the erne, the SDS... 

Linse [59] made a similar simulation for water near a charged surface with mobile counterions constituting an electric double layer such as in the interior of a reverse micelle formed with ionic surfactants in oil. He reported that water in the aqueous core of reverse micelles has a reduced rate of translational and rotational motions by a factor of 2-4. 

The experimental form factor P( ) shown in Fig. 12a can be expressed as P q) = [bcFc q,rc) + bsFs q,rc,R )], where bc,bs are the contrast factors for the core (c) and shell (5) with core radius and overall micelle radius R, whereas Fc q), F q) aiQ the scattering amplitudes of the core and shell, respectively. Under core contrast conditions (Z s 0), the expected first minimum for the compact sphere at high q values falls outside the ("/-range, whereas under shell contrast conditions the power-law behavior arising from blob (swollen PEO shell) scattering is observed. Hence, the dual colloid-polymer character of the particle is clearly reflected in Fig. 12a. 

To end this section, we briefly recall some results concerning the scattering intensity measured firom a collection of non-interacting particles like fringed micelles. For a non-spherical compact particle with dimension D in a space of dimension D, the asymptotic behaviour of the form factor is given by [16] ... 

---