Excess of surfactant

The type of behavior shown by the ethanol-water system reaches an extreme in the case of higher-molecular-weight solutes of the polar-nonpolar type, such as, soaps and detergents [91]. As illustrated in Fig. Ul-9e, the decrease in surface tension now takes place at very low concentrations sometimes showing a point of abrupt change in slope in a y/C plot [92]. The surface tension becomes essentially constant beyond a certain concentration identified with micelle formation (see Section XIII-5). The lines in Fig. III-9e are fits to Eq. III-57. The authors combined this analysis with the Gibbs equation (Section III-SB) to obtain the surface excess of surfactant and an alcohol cosurfactant. 

The reverse ME technique provides an easy route to obtain monodispersed metal nanoparticles of the defined size. To prepare supported catalyst, metal nanoparticles are first purified from the ME components (liquid phase and excess of surfactant) while retaining their size and monodispersity and then deposited on a structured support. Due to the size control, the synthesized material exhibits high catalytic activity and selectivity in alkyne hydrogenation. Structured support allows suitable catalyst handling and reuse. The method of the catalyst preparation is not difficult and is recommended for the... 

Again, as expected, in Figure 5 there is an excess of surfactant near the rear stagnation ring due to surface convection towards that point. Forward from that location, however, there is also a depletion relative to equilibrium adsorption. This is caused by the traveling wave in the rear bubble profile as demonstrated in Figure 2 and in Figure 7 to follow. 

Surfactants enable the polymer particles to disperse effectively without coagulation in the mortar and concrete. Thus, mechanical and chemical stabilities of latexes are improved with an increase in the content of the surfactants selected as stabilizers. An excess of surfactant, however, may have an adverse effect on the strength because of the reduced latex film strength, the delayed cement hydration and excess air entrainment. Consequently, the latexes used as cement modifiers should have an optimum surfactant content (from 5 to 30% of the weight of total solids) to provide adequate strength. Suitable antifoamers are usually added to the latexes to prevent excess air entrainment increased dosages causes a drastic reduction in the air content and a concurrent increase in compressive strength [87, 92-94]. 

In Eq. 38, the partial surface coverage, 0i, of the surfactant is defined as 01 = ri/Foo, where Ao is the surface excess of surfactant at saturation. K is the adsorption constant, which is a function of the surfactant and counterion adsorptions. The dependence is usually linear, yielding K = Ki + K20.1, where Ki and A are the equilibrium adsorption constants of the surfactant ions and their counterions. 

The settling rate of the dispersions in cyclohexane initially increases with AOT adsorption but later decreases. The initial increase is attributed to the formation of interparticle surfactant aggregates (Fig. 39A). At higher concentrations, the adsorbed molecules aggregate with excess of surfactant in solution rather than with molecules on the particle, so that flocculation ceases to occur and the dispersion is restabilized. The schematic representation of the surfactant assemblies at the interface is as shown in Fig. 39B. 

As mentioned previously, Bibette [95] has developed a very elegant method for the purification of coarse, polydisperse emulsions to produce monodisperse systems. This technique is based on the attractive depletion interaction between dispersed phase droplets, caused by an excess of surfactant micelles in the continuous phase. A phase separation occurs under gravity, between a cream layer and a dilute phase since the extent of the separation increases with increasing droplet diameter, a separation based on size occurs. By repeating this process, emulsions of very narrow size distribution can be produced. 

For a constant amount of nonionic surfactant, the interfacial tension at the planar oil-water interface, for the same amounts of oil and water, passes through a minimum when plotted against the hydrophilic-lipophilic balance (HLB). The emulsion stability passes through maxima in the W/O and O/W ranges and through a minimum between the two at the phase inversion point. The minima in the two cases coincide. These observations are explained on the basis of thermodynamics. The stability of macroemulsions can be correlated with the surface excess of surfactant, which also passes through two maxima and a minimum between them [2.11]. 

If the next filling (k + 1) leads to a dissolved excess of surfactant (solute peak present in the voltammetric scan), then the amount is detected by thin-layer coulometry... 

However, increasing surfactant concentration has the drawback of reducing globule drop size and increasing the interfacial area available for mass transfer of both solute and water. This effect is enhanced in the case where the surfactant molecules themselves have an affinity for water [95,96]. If the surfactant concentration exceeds the critical micelle concentration (cmc), water transport in W/O/W systems by reversed micelles can occur [89,97]. An increase in concentration of some surfactants such as SPAN 80 also leads to an increase in the entrainment of the external phase during permeation promoted by an excess of surfactant molecules [71,98]. Miesiac et al. [99] found that in the case of penicillin G separation, the choice of surfactant could control not only the extraction rate, but also the back transfer rates of the hydrolysis products. 

Maximal and stable absorbance of the triple complex is obtained with a large excess of surfactant in relation to CAS. In these systems, ternary complexes are formed in which the ratio CAS Be is greater than in binary systems (without surfactant). Figure 9.1 shows the absorption spectra of Chrome Azurol S and the binary and ternary (with CTA) complexes of beryllium... 

Surfactants also modify product viscosity. At a low level, such as 0.15%, the viscosity increases, becoming hard to stabilize. At higher levels the product is stable and its viscosity decreases. Any excess of surfactant is not detrimental but useless and expensive. 

We specify the concentration of a solute in a bulk fluid as mass per unit volume denoted as c. As before, we designate the position of the interface so that there is no surface excess of the two pure bulk solvents. The concentration of surfactant, which we may denote as ca and cb, respectively, in the two bulk fluids, will exhibit a peak in the vicinity of the interface between and B. Hence, in a macroscopic continuum description, it is necessary to include a surface excess of surfactant on the interface. If we denote the local concentration as c(x, t), again defined as a mass per unit volume, then the total mass of surfactant per unit area of interface is... 

Surfactant Concentration. The first requirement is that sufficient surfactant is present to cover the total air surface produced (i.e., give it a surface load comparable to the plateau value rcxi). Assume an overrun of 300%, i.e., (p = 0.75, and an average bubble diameter g 32 = 60,um, this implies a specific surface area A = 6cp/d32 = 0.05 m2 per ml foam, or 0.2 m2 per ml liquid. Assume, moreover, that roo = 3 mg m 2 this corresponds to 0.6 mg of adsorbed surfactant per ml liquid. Since some excess of surfactant is needed to reach full surface coverage (cf. Figure 11.15b), we would need at... 

In this section, y is assumed constant. This means either that no surfactant is present (then single drops are considered) or that there is a large excess of surfactant. Furthermore, when speaking about drops, bubbles are also implied. Most of the theory discussed is only valid for small volume fractions. 

These relations are well obeyed for dilute emulsions with an excess of surfactant. Figure 11.9 gives some practical results. In part b, lower curve, the slope is indeed exactly —0.6. 

Most foam-forming surfactants, particularly those suitable for high-salinity conditions, are very hydrophilic and do not partition into oil, eliminating the first of the listed mechanisms. The amount of surfactant adsorbed at the oil—water interface depends on the surface excess of surfactant at this interface and on the amount of interface present. Although the surface excess of surfactant at the oil—water interface can be estimated from interfacial tension data using the Gibbs adsorption equation, the amount of interface that is present is not easily accessible to measurement. 

As matrix polymer, an epoxy polymer based on 3,4-epoxycyclohexyl-methyl-3,4-epoxycyclohexane carboxylate (epoxy monomer), cured by hexahydro-4-methylphthalic anhydride at a molar ratio of 0.87-1.0 was used. To this mixture a nanofiller, MMT (Cloisite 30B) was added. Before this the nanofiller was mixed with denatured ethanol for removal of any excess of surfactants from the silicate platelets surface. This mixture was then centrifuged at 5,000 rpm for 10 min prior to the decanting of the ethanol. After Cloisite SOB addition the mixture was stirred in a mixer at... 

Phospholipid-stabilized intravenous emulsions have been widely used for parenteral nutrition and have also been introduced as drug carrier systems, especially for lipophilic compounds. The aim of the authors in the next papers we review here (50,51) was to consider in detail various mediods, c.g., PCS. nuclear magnetic resonance (NMR). transmission electron micnoscopiy (TEM). and small-angle x-ray diffraction studies (SAXS), to determine parameters related to the internal structure of the particle in a model intravenous emulsion stabilized by phospholipids. An emulsion with an extremely high fat load and a classical emulsifier was chosen. PCS measurements were used to derive a particle size distnbu-tion and this was then us ) to calculate the total oil droplet surface area. The result indicated that there should be an excess of surfactants of 150%. Such an excess was not confirmed by either NMR or SAXS measurements and the dis-... 

In this process, an aqueous solution of a water-soluble monomer (e.g., acrylamide) is dispersed in an organic continuous phase using an excess of surfactant. Water-in-oil micelles are formed. The polymerization is initiated by oil-soluble initiators, and the mechanisms involved in this process are similar to those occurring in emulsion polymerization. The product is a dispersion of an aqueous solution of water-soluble polymer in an organic... 

Figure 1 is a schematic representation of precipitate flotation with small bubbles and surfactant ions having opposite charge to the precipitate surface. The hydrophilic groups of surfactant ions are orientated toward the surface of the precipitate, and hence the precipitate is made effectively hydrophobic. Small bubbles are easily trapped on the surface of the precipitate and flotation is achieved. An excess of surfactant serves to form a stable foam layer that prevents the redispersion of the floated precipitate into the bulk solution (see Figure 2). 

---