Surfactant incorporation

The application range of cSFC-DFI-MS (Table 7.41) appears to be restricted either to the analysis of low-MW substances or to problems related to high-MW samples where low detection limits are not needed [124,444,445], The analysis of surfactants [446] by SFC-MS is frequently performed to demonstrate the feasibility of newly developed interface technology for practical applications. A rugged cSFC-MS method has been developed for the analysis of ethoxylated alcohols (AEs), which are non-ionic surfactants incorporated into a wide variety of industrial and consumer products [447]. cSFC-DFT-DFS was used for the analysis of low-MW, thermally unstable peroxides, and the higher-MW surfactants Triton X-100 and... 

Also, other dependent variables associated with CO2-foam mobility measurements, such as surfactant concentrations and C02 foam fractions have been investigated as well. The surfactants incorporated in this experiment were carefully chosen from the information obtained during the surfactant screening test which was developed in the laboratory. In addition to the mobility measurements, the dynamic adsorption experiment was performed with Baker dolomite. The amount of surfactant adsorbed per gram of rock and the chromatographic time delay factor were studied as a function of surfactant concentration at different flow rates. 

Figure 9. An idealized model for the cyclic oxidation-reduction process using thiol-functionalized surfactant, incorporated into DODAC vesicles together with Rh-coated colloidal CdS, for sustained hydrogen generation under visible light irradiation in one part of the cycle.

In the second approach to self-assembly of polymer-silica nanocomposites, polymerizable surfactants are employed both to direct self-assembly into ordered mesophases and to serve as organic monomers which can be subsequently polymerized. For instance, Brinker et al. developed nonionic surfactants incorporating diacy-telene groups which could be polymerized upon irradiation by UV light.68 69 Similarly, poly(thiophene)70 and poly(pyrrole)71 have been successfully integrated into silica nanostructures in this manner. Importantly, this in situ polymerization produces isolated molecular wires, rather than clustered bundles of conductive polymer.70... 

While the presence of surfactants is advantageous due to an increase in cellular membrane permeability, which facilitates drug absorption and bioavailability [218], caution needs to be taken in relation to the amount of surfactant incorporated, as high concentrations can lead to ocular toxicity. In general, nonionic surfactants are preferred over ionic ones, which are generally too toxic to be used in ophthalmic... 

Similar to all other colloidal delivery systems discussed above it was hypothesized by numerous research teams that a positive charge (provided by cationic surfactants [220]) would increase the ocular residence time of the formulation due to electrostatic interactions with the negatively charged mucin residues. However, toxicological studies contradicted this assumption regarding the ocular effects, and so far there has been no publication demonstrating a distinct beneficial effect of charged surfactants incorporated into MEs. 

Lawrence (1937) first noted that the site of incorporation of solubilized molecules depended on their relative hydrophobic and hydrophilic tendencies. The solubilizate may be entrapped in the hydrocarbon core of the micelle, be oriented radially in the micelle with its polar group buried (deep penetration) or near the surface (short penetration), or be adsorbed on the surface of the micelle. Additionally, for non-ionic surfactants, incorporation of the solubilizate can occur in the polyoxyethylene shell of the surfactant. Fig. 3 illustrates several modes of solubilizate incorporation. It is important to realize, however, that solubilization, like micelle formation, is not a static but a dynamic equilibrium process. 

Insoluble pigment soils, such as clays or other particulate solids, are removed during cleaning from the fiber surfaces with the help of surfactants. In both cleaning systems, surfactants incorporate this type of soil into the micelles to form relatively stable suspensions to prevent the redeposition of soil onto the textile (12). 

However, surfactants incorporated into the electrolyte solution at concentrations below their critical micelle concentration (CMC) may act as hydrophobic selectors to modulate the electrophoretic selectivity of hydrophobic peptides and proteins. The binding of ionic or zwitterionic surfactant molecules to peptides and proteins alters both the hydrodynamic (Stokes) radius and the effective charges of these analytes. This causes a variation in the electrophoretic mobility, which is directly proportional to the effective charge and inversely proportional to the Stokes radius. Variations of the charge-to-hydrodynamic radius ratios are also induced by the binding of nonionic surfactants to peptide or protein molecules. The binding of the surfactant molecules to peptides and proteins may vary with the surfactant species and its concentration, and it is influenced by the experimental conditions such as pH, ionic strength, and temperature of the electrolyte solution. Surfactants may bind to samples, either to the... 

The homopolymerization of reactive surfactants in the form of assemblies, such as micelles or liquid crystals, have been attempted as a way to freeze the structure and prepare various types of nano-sized materials. Polymerization of micelles has not been entirely successful, however. With both spherical and rod-like micelles, the polymerized aggregates were of much larger size than the original structures. With liquid crystals and, in particular, with vesicles, the result is more promising. Stable vesicles, of interest for drug administration, have been prepared by free-radical polymerization of preformed vesicles. Such vesicles need not be based entirely on polymerizable surfactants. Incorporation of... 

Paper Surfactant Incorporation method Incorporated molecule Comments... 

New surfactants incorporating paramagnetic oxo-vanadium centers, 84, were studied and some of the complexes were found to display both hexagonal and lamellar... 

The problem of droplet sliding in relation to spray retention has also been considered by Tadros. Spray retention increases as the volume applied increases, up to the point of incipient runoff. Above this point, the volume of spray retained begins to decline, and retention is determined by the movement of drops on the leaf surface. Factors influencing sliding include surface roughness, presence of hairs, leaf age, position on the leaf surface, environmental conditions, surfactant incorporation and concentration, droplet size and velocity, and wind speed. 

These experimental electrodes with surfactants incorporated into the membranes can be used to monitor the titration of nonionics (as their Ba complexes) with tetraphenylborate (133). Ivanov and Pravshin report that an electrode suitable for determination of nonionics can be made from a membrane of plasticized PVC containing either cetylpyrid-inium dodecylsulfonate or the complex of barium and tetraphenylborate ions with a nonionic (134). These electrodes also respond to ionic surfactants and respond much better to tetraphenylborate than to nonionic surfactants. Thus, they are most useful for monitoring the end point of a titration of the barium complexes of nonionics with tetraphenylborate. Ionic surfactants interfere in the titration. 

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