Surfactant phases

The foregoing is an equilibrium analysis, yet some transient effects are probably important to film resilience. Rayleigh [182] noted that surface freshly formed by some insult to the film would have a greater than equilibrium surface tension (note Fig. 11-15). A recent analysis [222] of the effect of surface elasticity on foam stability relates the nonequilibrium surfactant surface coverage to the foam retention time or time for a bubble to pass through a wet foam. The adsorption process is important in a new means of obtaining a foam by supplying vapor phase surfactants [223]. 

Emission spectra Phosphorescence Differential phase Surfactant enhancement (micelles, etc.)... 

For instance, the time course of SPE demonstrates that the solvent phase surfactant concentration steadily decreases (Fig. 3) [58]. The w/o-ME solution s water content decreases at the same rate as the surfactant [58]. The protein concentration at first increases, presumably due to the occurrence of Steps 2 and 3 above, but then decreases due to the adsorption of filled w/o-MEs by the solid phase (Fig. 3) [58]. Additional evidence supporting the mechanism given above is the occurrence of a single Langmuir-type isotherm describing surfactant adsorption in the solid phase for several SPE experiments employing a given protein type (Fig. 4) [58]. Here, solid-phase protein molecules can be considered as surfactant adsorption sites. Similar adsorption isotherms occurred also for water adsorption [58]. 

The main advantage to the Winsor system is its heuristic feature of treating all cohesive interactions in a two-phase surfactant system. However, to date only the simple form of Equation 22 has been exploited quantitatively (21, 23) as... 

System B Aqueous Phase (Surfactant + H2O with or without n-Buta-... 

Figure 4. Variation of y of the systems. A, aqueous phase surfactant + H O oil phase toluene with pendant drop method (24 °C). Concentration of detergent = 20 g/L. NaDOC (4) NaDOC + 8% n-butanol(A) NaDDS ( ) NaDDS + 8% n-butanol (O). B, aqueous phase surfactant + H2O oil phase n-heptane by pendant drop method 25 °c). Key same as for 4A.

System C Aqueous Phase Surfactant + H2O Oil Phase n-Alcohol... 

Figure 8.6 Comparison of the influence of non-ionic Ci2E6 (hexaoxyethyl-ene ft-dodecyl ether) or anionic SDS (sodium dodecyl sulfate) on adsorbed amount of p-lactoglobulin at the air-water interface (0.1 wt% protein, pH = 6, ionic strength = 0.02 M, 25 °C) as determined by neutron reflectivity measurements. Protein surface concentration is plotted against the aqueous phase surfactant concentration ( ) Ci2E6 ( ) SDS. Reproduced from Dickinson (2001) with permission.

HOC distribution coefficients (KD) between the immobile and mobile compartments varied as a function of solution chemistry and surfactant dose, KD values increased with increasing surfactant dose at low surfactant concentrations, but decreased at higher doses. This trend indicates that competition for HOC partitioning occurs between sorbed- and micellar-phase surfactants. Overall, the results of this study demonstrate that retardation of HOCs by surfactants sorbed to the solid phase can be significant and must be considered for proper evaluation of treatment/remediation alternatives that use surfactants. 

In Section 3.2 it was shown that surfactants can influence the magnitude of Kp. To use equation (3) to simulate changes in Kp, the following information is required 1) the aqueous surfactant concentration in the CFSTR as a function of time 2) the sorbed phase surfactant concentration in each of the NK sites 3) the magnitudes of Kmn and Kmc for each surfactant and, 4) the magnitude of Ks. Unfortunately, the required information to incorporate equation (3) into the distributed-rate model was not determined for this study. As a result, the influence of the surfactants on the distribution coefficient was not considered. 

Squalane was first pumped through the column in an upflow mode to saturate all extra-fiber pore space. The middle phase surfactant system (10% SDBS/17% IPA/12.4% NaCl/dodecane) was then pumped through the column in a downflow mode. The middle phase and squalane flow rates were 6.32 ml./min and 3.16 ml/min., respectively. The squalane and middle phase residence times in the column were 88.6 min. and 15.8 min., respectively. 

As mentioned above, the appearance of black spots (black films) is observed in films from soluble surfactants. It is believed that the solubility of these substances is a necessary condition for formation of black foam films. That is why it is interesting to produce black films, especially NBF, from insoluble (or poorly soluble) surfactant monolayers. Bilayer lipid films formed in aqueous medium from insoluble in organic phase surfactants have been studied largely [e.g. 390]. 

The spectra clearly show that the adsorption of charged surfactants at the CCLj/H20 interface at nanomolar aqueous phase surfactant concentrations results in a significant modification of the interfacial water behaviour. Wilhelmy balance surface pressure measurements [89] show that at these concentrations (headgroup areas of >4000 molecule ), the water molecules responsible for the observed spectral... 

Figure (3) shows the solubilization parameters as functions of water concentration for SDS/2- entanol ratios of 0.25 and 0.40 at 25 C. The solubilization parameters are defined as Vo/Vs and Vw/Vs, where Vo, Vs and Vw are the volumes of organic phase, surfactant and aqueous phase in the microemulsions. The parameters are related to the drop size and also interfacial torsions f7.23). The bicontinuous phase is located around the composition range corresponding to equal values of solubilization parameters. The solubilization parameters are dependent on the initial surfactant and/or cosurfactant concentration. Similar dependence has been observed in other systems as a function of salinity and pH (7.231. Conductivity measurements performed as a function of water content indicate an S-shaped curve as shown in Figure (4). This is typical of microemulsions showing transition from oil-continuous to bicontinuous to water-continuous microstructure with increasing water content. 

In the two-phase region, the type II(+) system has an oil-rich micellar phase in equilibrium with an excess brine phase. Surfactant is found almost exclusively in the oil-rich phase, and the concentration of surfactant in that phase can greatly exceed the concentration of surfactant in the injected chemical slug. In the type II(+) environment, the micellar phase remains miscible with the oil but is immiscible with the brine. Oil continues to be recovered by a misciblelike process. The opposite occurs if the phase environment is type II(-). The brine-rich micellar phase is immiscible with the oil phase, and oil recovery is by low IFT immiscible displacement. 

Water phase, containing Non-aqueous phase Surfactant Method k,/kT Ref. 

Figure 4 showed the solubilization (i.e., mass fraction in liquid phase) of phenanthrene with the C12 E4 surfactant, Brij 30, in 1 8 (g of soihmL of water) soil-water systems. Phenanthrene solubilization in the soil-water system was observed only at a surfactant dose greater than about 0.0026 mol/L, about 0.1% (v/v), which is many times greater than the pure aqueous CAC value for C12E4 of 8.3 X 10 % (v/v). The surfactant doses reported in Figures 4 and 6 refer to the bulk addition of surfactant to water, and the liquid-phase surfactant concentrations are smaller than bulk surfactant doses because of surfactant sorption onto soil. 

Some of the most interesting examples of self-assembly arise at the interfacial region between two bulk phases. Surfactant molecules, for example, tend to concentrate at interfaces, and self-assembly can give rise to intricate patterns and structures. 

Actually, we should separate inverse gas chromatography into inverse gas-liquid chromatography and inverse gas-solid chromatography. The obvious basis of such discrimination is the state of the column content being examined. Polymers and their mixtures, commercial stationary phases, surfactants represent liquids (at the measurement temperature) involving a mixed mechanism of the retention of the test solutes. Modified silicas are examples of solids that have been studied, and, in this case, adsorption effects predominate, while solution partition in graft chains seems to be negligible. These problems will be discussed in details by Papirer and Balard in another chapter of this book. 

Hirasaki, G.J., 1981. Application of the theory of multicomponent, multiphase displacement to three-component, two-phase surfactant flooding. SPEJ (April), 191-204. 

Use of liquid crystalline phases Surfactants produce liquid crystalline phases at high concentrations. Three main types of Hquid crystals can be identified hexagonal phase (sometimes referred to as middle phase) cubic phase and lamellar (neat phase). All of these structures are highly viscous and also show elastic responses. If produced in the continuous phase of suspensions, they can eliminate sedimentation of the particles. These Hquid crystalline phase are particularly useful for application in liquid detergents which contain high surfactant concentrations. Their presence reduces sedimentation of the coarse builder particles (phosphates and silicates). 

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