Micelles of surfactants

Rod-like micelles of surfactant molecules with a liquid-crystalline order. The aqueous solution is located between the micelles. Spheres = hydrophilic ends of the surfactant molecules, black zigzag lines = long alkyl groups... 

I luorophorcs having lower oxidation potentials also enhance the PO-CL reaction. The addition of these compounds to the postcolumn reagent is very effective so as to increase the sensitivity. The attempt to enhance CL intensity using micelles of surfactants has also been reported [33], but it has yet not been applied to HPLC. 

VE Yushmanov, JR Perussi, H Imasato, M Tabak. Interaction of papaverine with micelles of surfactants with different charge study by H-l-NMR. Biochim Biophys Acta-Biomembrans 1189 74-80, 1994. 

P. Fontaine, M. Goldmann, P. Muller, M.C. Faure, O. Konovalov, M.P. Krafft, Direct evidence for highly organized networks of circular surface micelles of surfactant at the air/water interface, J. Am. Chem. Soc. 127 (2005) 512-513. 

Work Is presently under way to extend the above model so as to extract from the experimental data the relevant parameters from a least-squares analysis (13). This model should be applicable to non-lonlc and Ionic systems. In the latter case, an extra term Is required to account for the shift In the CMC of solute 2 due to the sal-tlng-out of the monomers of 2 by solute 3 (7 ). The model In Its present form can still be used to estimate the thermodynamic properties of solute 3 In the micelle of surfactant 2 by adjusting the parameters to get a good fit with the experimental data. 

Martinek, K., Levashov, A. V, Klyachko, N. L., Pantin, V. L, and Berezin, I. V. (1981). The principles of enzyme stabilization. 6. Catalysis by water-soluble enzymes entrapped into reversed micelles of surfactants in organic solvents. Biochem. 

Once the dirty spot is removed from the substrate being laundered, it is important that it not be redeposited. Solubilization of the detached material in micelles of surfactant has been proposed as one mechanism that contributes to preventing the redeposition of foreign matter. Any process that promotes the stability of the detached dirt particles in the dispersed form will also facilitate this. We see in Chapter 11 how electrostatic effects promote colloidal stability. The adsorption of ions —especially amphipathic surfactant ions —onto the detached matter assists in blocking redeposition by stabilizing the dispersed particles. Materials such as carbox-ymethylcellulose are often added to washing preparations since these molecules also adsorb on the detached dirt particles and interfere with their redeposition. 

The pH value will control the condensation of silica, so the pH value should be adjusted to form monomer then oligomer of silica in order to obtain its condensation and polymerization around the micelles of surfactant Under acidic conditions, silica source such as... 

The micellization of surfactants has been described as a single kinetic equilibrium (10) or as a phase separation (11). A general statistical mechanical treatment (12) showed the similarities of the two approaches. Multiple kinetic equilibria (13) or the small system thermodynamics by Hill (14) have been frequently applied in the thermodynamics of micellization (15, 16, 17). Even the experimental determination of the factors governing the aggregation conditions of micellization in water is still a matter of considerable interest (18, 19) and dispute (20). 

Fig. 1.2. Dependence of free-energy changes (AG° mic) of micellization of surfactants in high, intermediate, and low-polar solvents. Normal micelle (M) to reverse micelle (RM) transition as function of polarity (e) of the medium. Surfactants in a medium of optimum dielectric constants 38 to 41 do not aggregate but remain in the monomeric state (n)...

Little and Singleterry (7) have published an interesting study on micellization of surfactants in a variety of solvents. Their data show that the better the solvent is for the surfactant, the less tendency there is for the surfactant to form aggregates or micelles. Yet to be determined is the effect of this micellization on emulsification properties. 

The emulsion of a fatliquor should not be too stable. The leathermaker wants to control its depth of penetration into the leather by the tendency of the surfactant to adsorb to the protein of the hide. This adsorption depletes the micelles of surfactant, causing the emulsion to break before it permeates the interior of the hide, releasing the oil somewhat superficially. The untreated interior thereby retains its stiffness, but with only a small mechanical moment. The product is then firm but resilient (not like cardboard). The released oil, with the surfactant tightly bound to the fibers, also resists being washed out of the leather by water. Suede leather, on the other hand, requires full penetration of the fatliquor and, therefore, an emulsifier that does not bind tightly to the protein. 

Because of the potentially useful pharmacological and biological applications of phenothiazine derivatives, it is very important to investigate the physicochemical aspects of their interactions and aggregations within organized media, such as CDs and micelles of surfactants. As a consequence, several literature studies have been reported in this field [35-44],... 

The phase behavior of surfactant formulations for enhanced oil recovery is also affected by the oil solubilization capacity of the mixed micelles of surfactant and alcohol. For low-surfactant systems, the surfactant concentration in oil phase changes considerably near the phase inversion point. The experimental value of partition coefficient is near unity at the phase inversion point (28). The phase inversion also occurs at the partition coefficient near unity in the high-surfactant concentration systems (31). Similar results were also reported by previous investigators (43) for pure alkyl benzene sulfonate systems. 

In some cases, solubilization of physiologically active materials enhances their potency in other cases, it diminishes their potency. Moreover, the use of surfactants in preparations that are ingested by organisms may increase their solubilization of other physiologically active undesirable materials, such as bacterial toxins or carcinogens. Solubilization may also inactivate preservatives in pharmaceutical preparations by incorporating the former into the micelles of surfactants used in the formulation. 

The value of 4> can also be obtained using the data for micellization of surfactants in which the surfactant is transferred from aqueous phase to an essentially hydrophobic phase. Table 2.12 lists transfer free energy data for some fatty acids and hydrocarbons. 

Association CoUoid A dispersion of colloidal-sized aggregates of small molecules. These are lyophilic dispersions. Example micelles of surfactant molecules in water. 

Figure 4. (a) Surfactants AOT (AerosoUOT) Sodium bis (2-ethyl-l-hexyl)sulfosuccinate, surfactant A (sodium bis (2,4,4-trimethyl-1-pentyl)sulfosuccinate) and surfactant B (sodium bis (3,5,5-trimethyl-1-hexyl) sulfosuccinate. (b) SANS data obtained after subtracting the cell sc-C02 background for surfactant K as a function of concentration at 0.15 ( ) and 0.10 (O) mol dm . T - 32X1 and 500 bar. The fits are to a polydisperse sphere model with = 14 1A and = 0.20 (footnote 37). (c) UV-vis spectrum of dimidium bromide dispersed in SC-CO2 with reversed micelles of surfactant B at 40X1 and 500 bar. The surfactant concentration is 0.025 mol dm. Reproduced with permission from Journal of the American Society, 2001, 123, 988-989. Copyright 2001 Am. Chem. Soc. 

In fact, the value of (ca. 10" g/dL) is exactly that found for a wide range of nonionic surfactants (9). Thus, the same thermodynamic forces that cause micellization of surfactants or phase separation of hydrophobic solvents appear to govern the solution properties of HMHECs (9). 

Incorporation of long-chain hydrocarbon hydrophobes into a cellulose ether backbone leads to an interesting new class of polymeric surfactants. Their enhanced solution viscosity can be explained in terms of intermolecular associations via the hydrophobe moieties. Entropic forces cause the polymer hydrophobes to cluster to minimize the disruption of water structure. The same thermodynamic principles that are used to explain the micellization of surfactants can be applied to explain the solution behavior of HMHEC. HMHECs interact with surfactants that modify their solution viscosities. The chemical nature and the concentration of the surfactant dictate its effect on HMHEC solution behavior. The unique rheological properties of HMHEC can be exploited to meet industrial demands for specific formulations and applications. 

FIG. 1 Phase diagram for Aerosol OT (AOT)-water-octane system. The boundaries of each individual phase were determined with 50 mM phosphate + 50 mM acetate buffer as an aqueous component (—). (From Ref. 2.) LI, L2 normal and reverse micelles of surfactant, respectively D, F liquid crystalline mesophases with lamellar and reverse hexagonal packing of surfactant molecules, respectively. Concentrations of all components are expressed as %(w/w). Cross-section of a type shows an example of the variation of water content at constant surfactant-to-organic solvent ratio cross-section of p type shows an example of the variation of organic solvent content at constant water-to-surfactant molar ratio. 

Protein (enzyme) incorporation into reverse micelles of surfactant in organic solvents may be achieved by one of the following methods. 

The phase behavior of surfactant formulations for enhanced oil recovery is also affected by the oil solubilization capacity of the mixed micelles of surfactant and alcohol. For low concentration surfactant systems, the surfactant concentration in the oil phase changes considerably near the phase inversion point. 

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