Surface other surfactants

In contrast to SDS, CTAB and C12E7, CufDSjz micelles catalyse the Diels-Alder reaction between 1 and 2 with enzyme-like efficiency, leading to rate enhancements up to 1.8-10 compared to the reaction in acetonitrile. This results primarily from the essentially complete complexation off to the copper ions at the micellar surface. Comparison of the partition coefficients of 2 over the water phase and the micellar pseudophase, as derived from kinetic analysis using the pseudophase model, reveals a higher affinity of 2 for Cu(DS)2 than for SDS and CTAB. The inhibitory effect resulting from spatial separation of la-g and 2 is likely to be at least less pronoimced for Cu(DS)2 than for the other surfactants. 

CMC), reverses the effect that the surfactant has on contact angle at lower concentrations, and at or above the CMC there is no further lowering of surface tension. At the higher concentrations, the surfactant loses some of its beneficial effect on dewateriag, as shown ia Figure 5. The beneficial effects of surfactants on dewateriag are most pronounced ia cakes that have been partially deslimed or ia cakes of partially hydrophobic particles (eg, flotation concentrates) that are adsorbed onto each other. Surfactants at or above CMC have Httle practical effect on extremely fine cakes, where pores are small and the cake has no further opportunity to consoHdate. A number of filter cakes do not respond to surfactant addition at any level. 

The CMC of commercial AOS and other surfactants at 40°C has been determined by Gafa and Lattanzi [6] who plotted the surface tension of aqueous surfactant solutions against concentration. The surface tensions were determined with the ring method according to du Nouy. Table 5 gives their CMC values in mmol/L and the surface tension at the CMC in mN/m. Table 5 also contains CMC values of isomerically pure sodium alkyl sulfates, sodium alkylbenzene-sulfonates, sodium hydroxyalkanesulfonate, and sodium alkenesulfonates at 40°C, taken from the literature [39 and references cited therein]. 

The applications of a-sulfo fatty acid esters are widely spread as for other surfactants. They can be used in detergents, cleansers, and cosmetic products as well as in the building industry and for the production of synthetic materials and agrochemicals. The main properties for these applications are surface activity, wetting ability, hard water stability, lime soap dispersion power, and good human and environmental safety profiles. 

Phosphorus-containing surfactants are amphiphilic molecules, exhibiting the same surface-active properties as other surfactants. That means that they reduce the surface tension of water and aqueous solutions, are adsorbed at interfaces, form foam, and are able to build micelles in the bulk phase. On account of the many possibilities for alteration of molecular structure, the surface-active properties of phosphorus-containing surfactants cover a wide field of effects. Of main interest are those properties which can only be realized with difficulty or in some cases not at all by other surfactants. Often even quantitative differences are highly useful. 

In 1997, a Chinese research group [78] used the colloidal solution of 70-nm-sized carboxylated latex particles as a subphase and spread mixtures of cationic and other surfactants at the air-solution interface. If the pH was sufficiently low (1.5-3.0), the electrostatic interaction between the polar headgroups of the monolayer and the surface groups of the latex particles was strong enough to attract the latex to the surface. A fairly densely packed array of particles could be obtained if a 2 1 mixture of octadecylamine and stearic acid was spread at the interface. The particle films could be transferred onto solid substrates using the LB technique. The structure was studied using transmission electron microscopy. 

PVP, a water soluble amine-based pol5mer, was found to be an optimum protective agent because the reduction of noble metal salts by polyols in the presence of other surfactants often resulted in non-homogenous colloidal dispersions. PVP was the first material to be used for generating silver and silver-palladium stabilized particles by the polyol method [231-233]. By reducing the precur-sor/PVP ratio, it is even possible to reduce the size of the metal particles to few nanometers. These colloidal particles are isolable but surface contaminations are easily recognized because samples washed with the solvent and dried in the air are subsquently not any more pyrophoric [231,234 236]. 

The toxicology of perfluorinated surfactants varies greatly most are harmless, whilst some are amongst the most toxic non-proteins known, the structural differences between the two often being relatively slight. Hence caution is needed in their use, even though they are so strongly surface-active that they can be used in much smaller quantities than other surfactants. 

Other cationic surfactants such as TTAB, DTAB, DODAB, STAC, CEDAB, and DDDAB have been used in CL reactions with less frequency. Thus, tetradecyltrimethylammonium bromide [TTAB] has been used to increase the sensitivity of the method to determine Fe(II) and total Fe based on the catalytic action of Fe(II) in the oxidation of luminol with hydrogen peroxide in an alkaline medium [47], While other surfactants such as HTAB, hexadecylpiridinium bromide (HPB), Brij-35, and SDS do not enhance the CL intensity, TTAB shows a maximum enhancement at a concentration of 2.7 X 10 2 M (Fig. 11). At the same time it was found that the catalytic effect of Fe(II) is extremely efficient in the presence of citric acid. With regard to the mechanism of the reaction, it is thought that Fe(II) forms an anionic complex with citric acid, being later concentrated on the surface of the TTAB cationic micelle. The complex reacts with the hydrogen peroxide to form hydroxy radical or superoxide ion on the... 

Key questions in these treatments are the constancy of a (or P) and the nature of the reaction site at the micellar surface. Other questions are less troubling for example the equations include a term for the concentration of monomeric surfactant which is assumed to be given by the cmc, but cmc values depend on added solutes and so will be affected by the reactants. In addition submicellar aggregates may form at surfactant concentrations near the cmc and may affect the reaction rate. But these uncertainties become less important when [surfactant] > cmc and kinetic analyses can be made under these conditions. In addition, perturbation of the micelle by substrate can be reduced by keeping surfactant in large excess over substrate. 

The potential for leaching or adsorption by plants has been thoroughly studied for LAS but not so much for the other surfactants (see Chapter 6.5). Thus, it is still a topic of recent studies, since this path represents a potential source for surfactants and their metabolites, which have not been entirely destroyed during sludge processing, to find a way into the terrestrial environment and from there into ground and surface water by leaching or run-off [53,54]. 

It was assumed that the experimental uncertainties followed Gaussian statistics with equal standard deviation a for all points. Then the standard deviation was determined as ct = (x /v), where v is the number of degrees of freedom in the fit. v is equal to the number of the experimental points less the number of parameters used in the minimization. The best fit with the Frumkin prediction has one free parameter (j6) and gives p =- 2.051 and CT = 0.41 mN/m. The standard deviation in surface tension is small, indicating that the fit with the Frumkin prediction is statistically significant. Similar best fits are obtained for the other surfactants of the homologue series of... 

Surface Interaction of Calcium and ATP with Phospholipids and Other Surfactants... 

Formation of free milk fat in DWM powder particles as a result of atomization and drying may also contribute significantly to poor solubility and dispersibility. Free milk fat, which is extractable from the powder by a 50 50 mixture (v/v) of ethyl and petroleum ether (Brunner, 1974), probably coats the powder particles and prevents their rehydration. The physical state of the milk fat, as controlled by the liquid-to-solid ratio and the presence of free milk fat on the particle surface, strongly influences DWM particle dispersibility. Spray coating of DWM particles with lecithin or other surfactants and dispersion in warm water improve their dispersibility. 

Property of liquid, whereby molecular forces at surface tend to minimize the contained volume, hence water droplets. Water has high surface tension, which makes it poor at wetting, thus requiring use of biodispersants and other surfactant materials in cooling water. 

The energetically unfavorable interactions of the hydrophobic tails with the water molecules are then minimized by the surfactants forming aggregates with other surfactant molecules. In those aggregates, the hydrophilic headgroups remain solvated by water molecules while the hydrocarbon moieties are shielded from water and create a hydrophobic microenvironment. Examples of these spontaneously formed aggregates are micelles and lamellae. The intersection of the extrapolations of the linear parts of the surface tension curve (Figure 17.2) is the critical micelle concentration (CMC). 

Attempts to correlate the adsorption data of other surfactants such as Alipal EP-110 and NaLS on the three latex surfaces in a similar manner failed because of the more complex and specific interactions observed in these systems. Equation 2 can adequately describe the adsorption data of surfactants at polymer/ water interfaces, provided that the free energy of the interface is related to the free energy of adsorption and there are no specific interactions between surfactant and interface (15). 

More commonly, demulsifiers are surface-active substances (surfactants) that have the ability to destabilize emulsions. This involves reducing the interfacial tension at the emulsion interface, often by neutralizing the effect of other surfactants that are stabilizing the emulsion. An example is antagonistic action - the addition of an O/W promoter to break a W/O emulsion (see sensitization in Section 5.4). Mikula... 

Under some conditions, mlcroemulslons form (284.285). In addition to these surface active extractants, many extraction schemes also have some other surfactants present (such as those given in Table V) that can form reversed micelles in the organic phase (1.4.5.283.330). The dialkylnaphthalene sulfonates (see Table V, anionic surfactant section) have been especially useful in this regard (263). 

The most widely used emulsion solvent evaporation method for preparation of nanoparticles using PLGA requires surfactants to stabilize the dispersed particle [23]. This method often has a problem that the surfactant remains at the surface of the particles and is then difficult to remove when PVA is used as surfactant. Other surfactants such as the span series or tween series, PEO, etc. are also used... 

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