Phase behavior of aqueous surfactant

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). 

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. 

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

L2 Olsson, M., Bostrom, G., Karlson, L., and Piculell, L., Added surfactant can change the phase behavior of aqueous polymer-particle mixtures, Langmuir, 21, 2743, 2005. 

Kaler EW, Herrington KL, Miller DD, Zasadzinski JAN (1992) In Kaler EW, Herrington KL, Miller DD, Zasadzinski JAN (eds) Phase Behavior of Aqueous Mixtures of Anionic and Cationic Surfactants Along a Dilution Path Kluwer Academic Publishers, Dordrecht, pp 571-577... 

PAN Pandit, N.K., Kanjia, J., Patel, K., and Pontikes, D.G., Phase behavior of aqueous solutions containing nonionic surfactant-polyethylene glycol mixtures, Int. J. Pharm., 122, 27, 1995. 

In summary, the above studies provide the equilibrium phase diagram of the Ci2MG-water system below 80°C. This work established, in addition, that the cloud point boundary is absent below 100 °C. (This is the boundary of the liquid/liquid miscibility gap commonly found in the diagrams of nonionic surfactant water systems). The absence of the cloud point boundary is significant with respect to analysis of the intrinsic hydrophilicity of this poly functional group [2]. The kinetic and nonequilibrium aspects of the phase behavior of aqueous C12MG mixtures will now be considered. 

Herrington, K.L., Kaler, E.W., Miller, D.D., Zasadzinski, J.A., Chiruvolu, S. Phase behavior of aqueous mixtures of dodecyltrimethylammonium bromide (DTAB) and sodium dodecyl sulfate (SDS). J. Phys. Chem. 1993, 97(51), 13792-13802. Khan, M.N., Ismail, E., Yusoff, M.R. Effects of pure non-ionic and mixed non-ionic-cationic surfactants on the rates of hydrolysis of phenyl salicylate and phenyl benzoate in alkaline medium. J. Phys, Org. Chem. 2001,14, 669-676. 

R. G. Laughlin, The Aqueous Phase Behavior of Surfactants, Academic, London, 1994. 

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. 

Laughlin RG (1994) The aqueous phase behavior of surfactants. Academic, London... 

It is well known that the aqueous phase behavior of surfactants is influenced by, for example, the presence of short-chain alcohols [66,78]. These co-surfactants increase the effective value of the packing parameter [67,79] due to a decrease in the area per head group and therefore favor the formation of structures with a lower curvature. It was found that organic dyes such as thymol blue, dimidiiunbromide and methyl orange that are not soluble in pure supercritical CO2, could be conveniently solubihzed in AOT water-in-C02 reverse microemulsions with 2,2,3,3,4,4,5,5-octafluoro-l-pentanol as a co-surfactant [80]. In a recent report [81] the solubilization capacity of water in a Tx-lOO/cyclohexane/water system was foimd to be influenced by the compressed gases, which worked as a co-surfactant. 

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. 

The phase behavior of surfactant systems is particularly complex because of the existence of numerous lyotropic (solvent-induced) liquid crystal phases (3). These phases, like liquids and crystals, are discrete states of matter. They are fluids, but their x-ray patterns display sharp lines signifying the existence of considerable structure. They are often extremely viscous because of their high viscosities and for other reasons they are difficult to study using conventional methods. This is evident from the fact that serious errors in the presumably well-established classical aqueous phase diagrams of soaps, sodium alkyl sulfates, monoglycerides, and... 

Micellar aggregates are considered in chapter 3 and a critical concentration is defined on the basis of a change in the shape of the size distribution of aggregates. This is followed by the examination, via a second order perturbation theory, of the phase behavior of a sterically stabilized non-aqueous colloidal dispersion containing free polymer molecules. This chapter is also concerned with the thermodynamic stability of microemulsions, which is treated via a new thermodynamic formalism. In addition, a molecular thermodynamics approach is suggested, which can predict the structural and compositional characteristics of microemulsions. Thermodynamic approaches similar to that used for microemulsions are applied to the phase transition in monolayers of insoluble surfactants and to lamellar liquid crystals. 

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. 

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). 

Finally, in the discussion of reverse microemulsion systems, mention should be made of one of the most widely studied systems. The surfactant, sodium bis(2-ethylhexyl) sulfosuccinate or Aerosol-OT (AOT), is one of the most thoroughly studied reverse micelleforming surfactants since it readily forms reverse micelle and microemulsion phases in a multitude of different solvents without the addition of cosurfactants or other solvent modifiers. The phase behavior of AOT in liquid alkane/water systems is already well documented. Indeed, the first report of the existence of the formation of microemulsions in a supercritical fluid involved an AOT/alkane/ water system. A The spherical structure of an AOT/nonpolar-fluid/ water microemulsion droplet is shown in Fig. 1. In the now well-known structure, it can be seen that the two hydrocarbon tails of each AOT molecule point outward into the nonpolar phase (e g., supercritical fluid). These tails are lipophilic and are solvated by the nonpolar continuous phase solvent whereas the hydrophilic head groups are always positioned in the aqueous core. 

Laughlin RG (1994). The Aqueous Phase Behavior of Surfactants, Academic Press, New York. Lequeux F, Candau SJ (1997). In Theoretical Challenges in the Dynamics of Complex Fluids, McLeish TCB (ed), NATO ASI Series E Applied Sciences, Vol 339, Kluwer, London, p 181. Linemann R, Lauger J, Schmidt G, Kratzat K, Richtering W (1995). Rheol Acta 34 440. 

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