Phase behavior aqueous surfactant solutions

Surfactant solution phase behavior is strongly affected by the salinity of the brine. In general, increasing the salinity of the brine decreases the solubility of the anionic surfactant in the brine. The snrfactant is driven out of the brine as the electrolyte concentration increases. Fignre 7.3 shows that as the salinity is increased, the surfactant moves from the aqneons phase to the oleic phase. At a low salinity, the typical snrfactant exhibits good aqueous-phase solubility. The oil phase, then, is essentially free of snrfactant. Some oil is solubilized in the cores of micelles. 

R Hansson and M. Akngren Interaction of Alkyltrimethylammonium Surfactants with Polyacrylate and Poly(Styrenesulfonate) in Aqueous Solution Phase Behavior and Surfactant Aggregation Numbers. Langmuir 10, 2115 (1994). 

The cell tests consisted of three steps (1) In the first step, the cell was charged with approximately equal volumes of CO2 and an aqueous solution of the test surfactant in reservoir brine. The desired behavior was formation of an emulsion-like dispersion of the C02-rich phase in the aqueous phase. (2) In the second step, a small amount of reservoir oil was added. Desirable surfactants formed three-phase dispersions in which both the C02 rich and oil-rich phases were dispersed in the aqueous phase. (The crude oil was not miscible with CO2.) (3) In the third step of the test, the amount of oil in the cell was increased until it was somewhat larger than the volumes of CO2 and of aqueous phase. Although relatively few surfactants passed this third step, the desired dispersion structure was believed to be droplets of the C02-rich phase dispersed in the continuous oleic phase, with films of aqueous surfactant solution encasing the dispersed droplets (42,43, S. L. Wellington, Shell Development Company, personal communication, November 13, 1987). "Foaminess" tests performed under these conditions correlated with the results of flooding experiments. Both nonionic alkoxylated surfactants and their anionic sulfonated derivatives were tested by these methods (42,43). 

The goals of this work have been to determine the effect of polymers on the phase behavior of aqueous surfactant solutions, prior to and after equilibration with oil, to understand the mechanism of the so-called "surfactant-polymer interactions (SPI) in EOR, to develop a simple model which will predict the salient features of the phase behavior in polymer-microeraulsion systems, and to test the concept of using sulfonate-carboxylate mixed microemulsions for increased salt tolerance. 

Phase Behavior of Aqueous Surfactant Solutions. The aqueous solu-tions contained 5 gm/dl TRS l0-4l0 as surfactant, and 3 gm/dl isobutyl alcohol as cosurfactant, unless otherwise indicated. The polymer concentration was varied from zero to 1500 ppm. The aqueous phase behavior in the absence of polymer is shown in Figure 2. The salinity is varied from 0.8 to 2.2 gm/dl NaCl in increments of 0.2 gm/dl. The phase behavior at lower salinities will be discussed later. The general trend is similar to the changes in textures reported for other commercial and model sulfonate solutions (26,27). 

Phase Behavior on Equilibration with Oil. Microemulsions are formed when the aqueous surfactant-cosurfactant solutions are mixed with oil, and allowed to equilibrate. Figure 5(a) shows the phase behavior when 5 ml aqueous surfactant solutions (without any polymer) were equilibrated with equal volumes of n-dodecane. The salinity was varied from 0.8 to 2.2 gm/dl NaCl in 0.2 gm/dl increments. At low salinities a lower phase microemulsion exists in equilibrium with excess oil. The middle phase microemulsion appears at about... 

Hansson P, Almgren M. Interaction of alkyltrimethylammonium surfactants with poly(acrylate) and poly(styrenesulfonate) in aqueous solution. Phase behavior and surfactant aggregation numbers. Langmuir 1994 10 2115-2124. 

Feng,Kunieda, H., Izawa, T., and Sakai, T. (2004) Effect of novel alkanolamides on the phase behavior and surface properties of aqueous surfactant solutions. /. Dispersion Sci. Tedinol, 25,1 10. 

Phase behavior experiments should be performed to identify surfactants with high contaminant solubilization, fast coalescence rates to classical microemulsions and minimal liquid crystal/gel/ macroemulsion forming tendencies over the expected range of conditions of temperature, electrolyte, surfactant, cosolvent and contaminant concentrations. The viscosity of both the aqueous surfactant solution that is injected and the microemulsion that forms when it mixes with and solubilizes the NAPL should be low, i.e. not much greater than the corresponding water (or polymer solution if polymer is added to the water). 

Most of the examples discussed are related to reversible (equilibrium) conditions. The behavior of the adsorption layer formed on hydrophobic methylated surfaces in aqueous surfactant solutions is shown in Figure 4.26a. Compression of the particles resulted in the retraction of the adsorption layer, which returned once the particles were separated. The situation is principally different in the case of adsorption from a nonpolar phase on polar particles, as is schematically shown in Figure 4.27b. The fixation of the adsorption layer by chemisorption, as in the case of the adsorption of amines on silicate glass, resulted in an adsorption layer that had its own strength, and a certain... 

There would appear to be no thorough systematic study of the defoaming effect of ultrasound (at frequencies > 20 Hz) as a function of acoustic pressure and frequency in the case of foams prepared from dilute aqueous surfactant solutions. This could be made with foam of different bubble sizes and low polydispersity to establish, for example, whether there exists a relation between frequency, bubble size, and defoaming. It should include consideration of the effect of foam age and therefore drainage. The application of the relevant method to additionally study the effects of the continuous phase viscosity could also be made. The mechanism of defoaming could be probed further if such studies could be combined with study of the effects of changes in the surface dynamic and rheological behavior of the surfactant solutions. 

Li H, Hao J (2007) Phase behavior of salt-free catanionic surfactant aqueous solutions with fullerene C60 solubilized. J Phys Chem B. Ill 7719-7724. 

It has also been shown [254] that a commercial petroleum sulfonate surfactant which consists of a diverse admixture of monomers does not exhibit behavior typically associated with micelle formation (i.e., a sharp inflection of solvent properties as the concentration of surfactant reaches CMC). These surfactants exhibit gradual change in solvent behavior with added surfactant. This gradual solubility enhancement indicates that micelle formation is a gradual process instead of a single event (i. e., CMC does not exist as a unique point, rather it is a continuous function of molecular properties). This type of surfactant can represent humic material in water, and may indicate that DHS form molecular aggregates in solution, which comprise an important third phase in the aqueous environment. This phase can affect an increase in the apparent solubility of very hydrophobic chemicals. 

For a given surfactant, the ability to form a single-phase w/o microemulsion is a function of the type of oil, nature of the electrolyte, solution composition, and temperature (54-58). When microemulsions are used as reaction media, the added reactants and the reaction products can also influence the phase stability. Figure 2.2.4 illustrates the effects of temperature and ammonia concentration on the phase behavior of the NP-5/cyclohexane/water system (27). In the absence of ammonia, the central region bounded by the two curves represents the single-phase microemulsion region. Above the upper curve (the solubilization limit), a water-in-oil microemulsion coexists with an aqueous phase, while below the lower curve (the solubility limit), an oil-in-water water microemulsion coexists with an oil phase. It can be seen that introducing ammonia into the system results in a shift of the solubilization... 

Puvvada, S., and D. Blankschtein. 1992a. Thermodynamic description of micellization, phase behavior, and phase separation of aqueous solutions of surfactant mixtijr fe.ys. Chenr96 5567-5579. 

Time - resolved spectra of a solid hydrocarbon layer on the surface of an internal reflection element, interacting with an aqueous solution of a nonionic surfactant, can be used to monitor the detergency process. Changes in the intensity and frequency of the CH2 stretching bands, and the appearance of defect bands due to gauche conformers indicate penetration of surfactant into the hydrocaibon layer. Perturbation of the hydrocarbon crystal structure, followed by displacement of solid hydrocaibon from the IRE surface, are important aspects of solid soil removal. Surfactant bath temperature influences detergency through its effects on both the phase behavior of the surfactant solution and its penetration rate into the hydrocaibon layer. 

Stuermer, A., Thunig, C., Hoffmann, H. and Gruening, B. (1994) Phase behavior of silicone surfactants with a comblike structure in aqueous solution. Tenside, Surfactants, Detergents, 31, 90-8. 

Extractions Based on the Phase Separation Behavior of Aqueous Micellar Solutions. The extraction and concentration of components in an aqueous mixture can sometimes be effected via use of appropriate surfactant systems that are capable of undergoing a phase separation as a result of altered conditions (i.e. temperature or pressure changes, added salts or other species, etc.). Two general types of such surfactant extraction systems will be described (i) those based on the cloud point phenomenon and (ii) those based on coacervation formation. 

Summary PDMS-6-PEO short-chain diblock copolymers were prepared via anionic ring-opening polymerization of cyclosiloxanes. Applying this method, various well-defined block copolymers with different compositions were synthesized and their phase behavior was investigated. The polymers predominantly showed lamellar phases in aqueous solutions. At small surfactant concentrations, vesicles were formed, as observed via cryogenic TEM. The aggregates of the diblock copolymers were used for the formation of lamellar thin films, applying the evaporation-induced self-assembly approach. 

At low salinities, the pseudoternary phase behavior is like that shown in Figure 19. Tie lines indicate a preferential solubility of the surfactant-alcohol mixture in brine. Also, the initial aqueous structure at composition D is a dilute dispersion of liquid crystal in an isotropic aqueous solution. The calculated... 

Table I. Phase behavior of polymer/surfactant-cosurfactant aqueous solutions as observed in polarized light...

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