Surfactant ratio

Emulsion polymerizations of vinyl acetate in the presence of ethylene oxide- or propylene oxide-based surfactants and protective coUoids also are characterized by the formation of graft copolymers of vinyl acetate on these materials. This was also observed in mixed systems of hydroxyethyl cellulose and nonylphenol ethoxylates. The oxyethylene chain groups supply the specific site of transfer (111). The concentration of insoluble (grafted) polymer decreases with increase in surfactant ratio, and (max) is observed at an ethoxylation degree of 8 (112). 

Lu B, Zheng Y, Scriven LE, Davis HT, Talmon Y, Zakin JL (1998) Effect of variation counterion-to-surfactant ratio on rheology and micro-structures of drag reducing cationic surfactant systems. Rheol Acta 37 528-548... 

Figure 2 schematically presents a synthetic strategy for the preparation of the structured catalyst with ME-derived palladium nanoparticles. After the particles formation in a reverse ME [23], the hydrocarbon is evaporated and methanol is added to dissolve a surfactant and flocculate nanoparticles, which are subsequently isolated by centrifugation. Flocculated nanoparticles are redispersed in water by ultrasound giving macroscopically homogeneous solution. This can be used for the incipient wetness impregnation of the support. By varying a water-to-surfactant ratio in the initial ME, catalysts with size-controlled monodispersed nanoparticles may be obtained. 

Mixed Admicelles. The total sur-factant adsorption o-f the two pure sur-factants and mixtures thereo-f on alumina are shown in Figure 3. The mixtures are at constant surFactant ratio in the Feed or initial solution, but not necessarily in the Final equilibrium solution. The concentration on the abscissa is the equilibrium concentration. The individual surFactant adsorption isotherms For the pure surFactants and in the mixtures are shown in Figures 4 and 5. The experiments were run at the same swamping electrolyte concentration as were the CMC data. 

Pons et al. have studied the effects of temperature, volume fraction, oil-to-surfactant ratio and salt concentration of the aqueous phase of w/o HIPEs on a number of rheological properties. The yield stress [10] was found to increase with increasing NaCl concentration, at room temperature. This was attributed to an increase in rigidity of films between adjacent droplets. For salt-free emulsions, the yield stress increases with increasing temperature, due to the increase in interfacial tension. However, for emulsions containing salt, the yield stress more or less reaches a plateau at higher temperatures, after addition of only 1.5% NaCl. 

Surfactants having an appropriate hydrophobic/hydrophilic balance (sodium bis(-2-ethylhexyl)sufosuccinate, or AOT, for example) undergo concentration-dependent self association in apolar solvents to form reversed or inverted micelles (Fig. 33) [256-262]. Reversed micelles are capable of solubilizing a large number of water molecules (AOT reversed micelles in hexane are able to take up 60 water molecules per surfactant molecule, for example). Reversed-micelle-entrapped water pools are unique they differ significantly from bulk water. At relatively small water-to-surfactant ratios (w = 8-10, where w = [H20]/[Surfactant]), all of the water molecules are strongly bound to the surfactant headgroups. Substrate solubilization in the restricted water pools of reversed micelles results in altered dissociation constants [256, 257, 263-265], reactivities [256, 258, 266], and reaction products [267]. 

NaBH4 reduction. Water surfactant ratio determined silver particle diameters... 

Surfactants are employed in nanoparticle suspensions. Chen et al. (2002) evaluated the pre paration of amorphous nanoparticle suspensions containing cyclosporine A using the evaporative precipitation into aqueous solution (ERAS) system. The effect of particle size was studied varying the drug surfactant ratios, type of surfactants, temperature, drug load, and solvent. Acceptable particle sizes suitable for both oral and parenteral administration were also studied. Additional articles in the nanoparticle delivery of poorly water-soluble drugs include Kipp (2004), Perkins et al. (2000), Young et al. (2000), and Tyner et al. (2004). 

It is generally accepted that the soft-core RMs contain amounts of water equal to or less than hydration of water of the polar part of the surfactant molecules, whereas in microemulsions the water properties are close to those of the bulk water (Fendler, 1984). At relatively small water to surfactant ratios (Wo < 5), all water molecules are tightly bound to the surfactant headgroups at the soft-core reverse micelles. These water molecules have high viscosities, low mobilities, polarities which are similar to hydrocarbons, and altered pHs. The solubilization properties of these two systems should clearly be different (El Seoud, 1984). The advantage of the RMs is their thermodynamic stability and the very small scale of the microstructure 1 to 20 nm. The radii of the emulsion droplets are typically 100 nm (Fendler, 1984 El Seoud, 1984). 

Effective pH values in soft-core RMs. Characterization of the acidity in the aqueous soft-core is important as ionizable compounds are solubilized in the water pool. The micellar core has a very high degree of organization of water. The water pool within reverse micelles is a different solvent than bulk water. The most interesting range of water content corresponds to rather small water pools (water-to-surfactant ratio of 3 to 10) in which peculiar properties of water cause the largest changes in behavior as compared to their behavior in bulk water. A water to surfactant ratio of 1 1 represents a very small, almost undetectable, quantity of... 

For given values of the control variables Xsw and. Xaw, the maximum in Xgo (or Xgw) was found, using the IMSL subroutine ZXMWD, by solving the implicit eq 3.1 in combination with eq 3.4. As mentioned in section 2, the area per surfactant molecule a, the alcohol-to-surfactant ratio gAi4 si, and the oil-to-surfactant ratio golgsi in the interfacial layer were selected as the three independent variables with respect to which the maximization was carried out. The total volume fraction 4>s of surfactant present in the microemulsion is given by... 

The maximum of Qf is determined with respect to the two independent variables, the area per surfactant molecule of the interface, aF, and the alcohol-to-surfactant ratio in the interfacial layer, (gAs/gsih- In contrast to that in the droplet-type microemulsion, the oil-to-surfactant ratio in the interfacial layer, (goi/gsi)F, is not an independent variable but is determined by the packing constraint (eq 2.7) for flat layers. 

Table 7.5. presents the results on foam stability depending on the hydrophile-hydrophobe surfactant ratio and kerosene concentration for transparent solutions. It should be noted that the direct measurement of the capillary pressure in the foam with a capillary... 

The Carboxylate/Alcohol System. A comparison between different alcohol solubility areas with different surfactants and water — reveals the fact that a minimum water/surfactant ratio... 

Figure 2. Effect of total surfactant concentration with varying surfactant ratio on polymerization rate...

The composition of mixed surfactant is designated by r, the surfactant ratio and expressed in moles SLS per mole of BC-840. This ratio can be adjusted as desired. 

To check the validity of this concept, the simplest and most straight-forward approach seemed to be to carry out rate studies of emulsion polymerizations with recipes of identical micellar sizes. Since, as mentioned previously, each specific value of surfactant ratio, r, of the mixed surfactant stands for a specific size of the mixed micelles, the experimental approach boils down to run several series of kinetic studies with different surfactant ratios between series, but with varying surfactant concentrations within each series. The standard recipe for such experiments was described in the Experimental Section. This standard recipe is essentially identical with the one used by Kamath ( ), Wang i9) and Letchford (15) with the exception of eliminating KOH. 

KOH affects the size of the changed micelles (12.16-18). For mixed surfactant systems, this effect may be different for different values of surfactant ratios of the mixed surfactants. Furthermore, it was observed, during the earlier period of the present study, that the dilute solutions of sodium lauryl sulfate beccime turbid in the presence of KOH, presumably due to alkaline hydrolysis. Therefore, KOH was not used in this study. 

By following identical experimental approach, seven other straight lines of such logarithmic plots were obtained with different surfactant ratios. Regression equation of the form... 

Since each of these 8 straight lines of the logarithmic plot of Rp vs Cg were obtained from a constant value of surfactant ratio, r, and thus a constant value of the size of the micelles, this series of experiments indicates that ... 

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