Surfactants phase properties

In this study we examined the influence of concentration conditions, acidity of solutions, and electrolytes inclusions on the liophilic properties of the surfactant-rich phases of polyethoxylated alkylphenols OP-7 and OP-10 at the cloud point temperature. The liophilic properties of micellar phases formed under different conditions were determined by the estimation of effective hydration values and solvatation free energy of methylene and carboxyl groups at cloud-point extraction of aliphatic acids. It was demonstrated that micellar phases formed from the low concentrated aqueous solutions of the surfactant have more hydrophobic properties than the phases resulting from highly concentrated solutions. The influence of media acidity on the liophilic properties of the surfactant phases was also exposed. 

The assessment of surfactant structures and optimal mixtures for potential use in tertiary flooding strategies in North Sea fields has been examined from fundamental investigations using pure oils. The present study furthermore addresses the physico-chemical problems associated with reservoir oils and how the phase performance of these systems may be correlated with model oils, including the use of toluene and cyclohexane in stock tank oils to produce synthetic live reservoir crudes. Any dependence of surfactant molecular structure on the observed phase properties of proposed oils of equivalent alkane carbon number (EACN) would render simulated live oils as unrepresentative. 

Understanding surfactant phase behavior is important because it controls physical properties such as rheology and freeze-thaw stability of formulations. It is also closely related to the ability to form and stabilize emulsions and microemulsions. Micelles, vesicles, mi-croemulsions and liquid crystal phases have all been used as delivery vehicles for perfumes or other active ingredients. 

Early researchers sought to choose appropriate surfactants for mobility control from the hundreds or thousands that might be used, but very little of the technology base that they needed had yet been created. Since then, work on micellar/polymer flooding has established several phase properties that must be met by almost any EOR surfactant, regardless of the application. This list of properties includes a Krafft temperature that is below the reservoir temperature, even if the connate brine contains a high concentration of divalent ions (i.e., hardness tolerance), and a lower consolute solution temperature (cloud point) that is above the reservoir temperature. 

The value of the 1.0X 1.5X brine foam volume ratio at 75 C may be taken as a measure of the sensitivity of surfactant foaming properties to aqueous phase salinity. Values of this ratio determined at 75 C in the presence of decane are summarized below ... 

Unlike previous one atmosphere foam test designs, the present test permits the effect of the oil phase on surfactant foaming properties to be determined. Refined hydrocarbons were used as model oil phases. Results summarized in Tables I and Figure 3 indicated that the presence of hydrocarbons decreased the foam stability. Examination of Table I indicated that the presence of a hydrocarbon substantially reduced the 75 C foam volumes produced by AES and AESo surfactants. 

Table II. Effect of an Oil Phase and Aqueous Phase Salinity on Surfactant Foaming Properties...

Surfactant foaming properties are related to oil phase composition. The composition of the residual oil will change in the course of a COj EOR project. The optimum COj mobility control agent may thus change during the course of the project. 

Internal Phase Composition As with the continuous phase, the internal phase properties also influence the properties of the ELM. Ionic strength, pH, and the presence of organic species will impact on the stability of the ELM. Emulsion liquid membranes work on the basis that the polar substances (usually high concentrations of acid or base) contained in the internal phase are impermeable to the membrane phase. However, the presence of the surfactant can cause the uptake of these compounds by the formation of reverse micelles [97]. 

The set of equations in the table may serve as starting points for further analyses. We note in passing that these equations are general and phenomenological no assumption whatever has been made about the properties of the surfactants, neither was it necessary to make a restriction with respect to the phase properties (i.e. one homogeneous phase or more phases at equilibrium with each other). There was no need either to make special provisions for charged mono-layers, because all double layers are electroneutral, the Donnan exclusion being accounted for by Extension to mixed monolayers (two surfactants) is... 

A second category of liquid crystals is the type produced when certain substances, notably the esters of cholesterol, are heated. These systems are referred to as thermotropic liquid crystals and, although not formed by surfactants, their properties will be described here for purposes of comparison. The formation of a cloudy liquid when cholesteryl benzoate is heated to temperatures between 145 and 179°C was first noted in 1888 by the Austrian botanist Reinitzer. The name liquid crystal was applied to this cloudy intermediate phase because of the presence of areas with crystal-like molecular stmcture within this solution. 

In summary, several phenomena occurring at the optimal salinity in relation to enhanced oil recovery by macro- and microemulsion flooding are schematically shown in Figure 18. It is evident that the maximum in oil recovery efficiency correlates well with various transient and equilibrium properties of macro- and microemulsion systems. We have observed that the surfactant loss in porous media is minimum at the optimal salinity presumably due to the reduction in the entrapment process for the surfactant phase. Therefore, the maximum in oil recovery may be due to a combined effect of all these processes occurring at the optimal salinity. 

A book by Laugh in [76] is a very valuable reference on the aqueous phase behavior of surfactants. It covers this vast area of science from the viewpoints of the role of phase science within physical science, physical chemistry (thermodynamics of immiscibility, phase diagrams, the phase rule, characteristic features of surfactant phase behavior, kinetic and mechanistic aspects of surfactant phase behavior, relative humidity), structures and properties of surfactant phases, molecular correlations (surfactant and nonsurfactant behavior in amphiphilic molecules, hydrophilicity, lipophilicity, proximate and remote substituent effects, influence of third components on aqueous surfactant phase behavior), the relationship of the physical science of surfactants to their utility, and the history of surfactant phase science. 

In order to emphasize the role of the inter facial films and to highlight the most recent viewpoints on the stability of microemulsions, sponge phases, and dilute lamellar phases, some of the experimental facts about phase behavior of microemulsion systems containing alcohol are reviewed in this chapter. The systems investigated consist of water, oil, alcohol, and sodium dodecylsulfate (SDS). In the next section, the theoretical aspects of the stability of surfactant phases are briefly discussed. Then in Secs. Ill and IV the effects of varying alcohol and oil chain lengths and the addition of a water-soluble polymer are examined. The examination of multiphase regions provides the location of lines of critical points or critical endpoints. This chapter also deals with the study of several physical properties in the vicinity of critical points. 

Many industrial products use mixtures of both surfactant and polymer molecules or surfactant and colloid. Although the effects of polymer on the phase behavior and structure of surfactant phases have begun to be investigated in microemulsions, lamellar phases, and vesicle phases, further experimental work in mixed systems is necessary to understand how the polymer or the colloid modifies the elastic properties of the surfactant film. 

The lowest interfacial tensions in Winsor systems have a different origin than that of the largest ones they do not depend on the surfactant film properties and are due to the nearness of a critical point. Close to the boundaries Winsor I Winsor III, S = S and Winsor III -> Winsor II, S = Si, the corresponding excess phase becomes slightly turbid. This is reminiscent of the vicinity of a critical point. This particular type of critical point, where... 

The PIT (with water and a given oil phase, i.e., hexadecane) was first correlated with the cloud point, i.e., the temperature at which a surfactant phase separates from u low concentration, c.g., 3%. surfactant solution (48). It is worth noting that the cloud point indicates a property of the surfactant, somehow the HLB. while the PIT takes into account the interaction with both the aqueous and oil phase. Early experimental evidence indicated that the PIT increased as the nonionic surfactant polyethylene chain length increased, increased as the hydrocarbon oil chain length increa.sed, and decreased as the salt concentration increased in the aqucou.s phase. Since the PIT is actually the physicochemical situation in which Winsor = I, and since an increase in temperature tends to reduce the Aiw interaction, the interpretation of the previously mentioned trends is siraighiforward when the numerator and denominator of Winsor R are equated. 

Part Two, Surfactants, contains chapters on the four major classes of surfactants, i.e. anionics, nonionics, cationics and zwitterionics, as well as chapters on polymeric surfactants, hydrotropes and novel surfactants. The physico-chemical properties of surfactants and properties of liquid crystalline phases are the topics of two comprehensive chapters. The industrially important areas of surfactant-polymer systems and environmental aspects of surfactants are treated in some detail. Finally, one chapter is devoted to computer simulations of surfactant systems. 

The two main properties of surfactant molecules are micelle formation and adsorption at interfaces. In Micellar Liquid Chromatography (MLC), the micelle formation property is linked to the mobile phase. Micelles play the role of the organic modifier in RPLC. Nonpolar solutes partition themselves between the micelle apolar core and the apolar bonded stationary phase. This partitioning will be the subject of Chapter 5. The surfactant adsorption property is linked to the stationary phase. A significant number of surfactant molecules may adsorb on the stationary phase surface changing its properties. The study of such adsorption and its associated problems is the main subject of this chapter. 

Various experiments indicate that properties of the microemulsion phase change continuously with increasing salinity as inversion from a water-continuous to an oil-continuous microstrucmre occurs. For instance, electrical conductivity decreases continuously with increasing salinity (Bennett et al., 1982). In addition, the self-diffusion coefficient of oil as measured by nuclear magnetic resonance (NMR) techniques increases from small values at low salinities where oil is the dispersed phase to a value comparable to that of the bulk oil phase near and above the optimal sahnity. The self-diffusion coefficient of water, in contrast, decreases from a value comparable to that in pnre NaCl brine below and near the optimal sahnity to mnch smaller values at high salinities where water is the dispersed phase (Olsson et al., 1986). Thus the surfactant phase is bicontinuous near the optimal sahnity, as originahy proposed by Scriven (1976) and subsequently confirmed by electron microscopy (Jahn and Strey, 1988). 

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