Surfactant based systems

Ward, A.J.I., Kinetics of solubilization in surfactant-based systems, in Solubilization in Surfactant Aggregates, Christian, S.D. and Scamehorn, J.E., Eds., Marcel Dekker, New York, 1995, chap. 7. Chen, B.H., Miller, C.A., and Garrett, P.R., Rates of solubilization into nonionic surfactant solutions. Colloids Surf. A, 128, 129, 1997. 

Whereas in simple aqueous solutions the carbomers and the cross-polymers show a significandy better efficiency, Table 5.2 shows that in surfactant-based systems this no longer holds true. The use levels indicated in the table are the quantities of polymer required to obtain a given apparent Brookfield LV-60 viscosity of about 3000 mPa s, and in all the anionic surfactants the results are more equitable for the different classes of polymer compared with the situation in water. In the case of the nonionic surfactant, the difference is still maintained, however. 

So, the disadvantages of working with polar aprotic solvents or with phase transfer catalysts can be avoided by the use of surfactant-based systems. Work-up procedures at high boiling temperatures or low vacuum, as in the case of many polar aprotic solvents, can be avoided by the selection of a suitable hydrophobic component. Since there are surfactants available which allow dispersion of all kinds of hydrophobic liquids in water, low boiling aliphatic or aromatic solvent can be used for formulation of the reaction medium. This allows a work-up without high-energy demand. 

In order to separate the phases of a surfactant-based system for product isolation and, where necessary, for catalyst recovery the appropriate phase region of the phase diagram has to be chosen first. Within this region the phase composition and the kinetics of phase separation are essential questions. Near to the phase boundaries the composition of the phases is rather similar and separation of the components will often be incomplete. The phase separation often takes a long time because of low interfacial tension and high stability of the emulsified two-phase system. The kinetics of phase separation depends sensitively on the temperature of the system, especially on the temperature distance to phase boundaries. Figure 5.15 shows a plot of separation times for a water-oil-non-ionic surfactant system as a function of the temperature. 

Although polymeric rheology control additives dominate the market for fracturing fluids, cationic surfactant-based systems have been introduced. Ethoxylated quaternary ammonium salts have been shown to afford viscoelastic aqueous fracturing fluids. The strength and temperature stability of the viscoelastic formulations depends upon the purity of the surfactant. These systems are claimed to break upon exposure to hydrocarbons, thereby affording clean-up behaviour superior to that available when using polymer-based fracture fluids. 

Aqueous solutions of dimer amidopropyl betaine are highly viscous, and are typically non-flowable above a betaine actives concentration of 5 wt%. They display interesting rheological phenomena (25). To achieve higher concentrations for shipment of this Gemini betaine, mixtures with cocamidopropyl betaine can be made. On this basis, concentrations of 25 wt% active matter are achievable. Dimer amidopropyl betaine shows an increased substantivity, compared to cocamidopropyl betaine, on fibres and is a very effective irritancy miti-gant in anionic-surfactant-based systems. 

Ward, A.J., Kinetics of solubilization in surfactant-based systems, in Solubilization in Surfactant Aggregates, 1995, p. 237. 

A basic question that might be raised here concerns whether objective criteria for establishing this quite detailed picture can be ascertained. We can seldom reach this level of description with regard to microstructure of surfactant-based systems when we rely on only calorimetric data. The salient features of such... 

The role of alcohol in surfactant-based systems is discussed later in this review. Here it is sufficient to say that alcohol molecules present at the interface of such a system may weaken the association between the surfactant and the outer interfacial water layers, although for the complete detachment of these... 

The thickness of the bound water layer in surfactant-based systems may be evaluated by several methods. In this review we focus on one that was originally derived from the interaction of interfacial water with solid surfaces. Gilpin [156] suggested the power law... 

VIII. The State of Water in Surfactant-Based Systems... 

Differential scanning calorimetry (DSC) is widely used for studying binary and multicomponent systems containing surfactants. Transition temperatures and enthalpies are often determined and used to draw the limits of existence of the different phases of surfactant-based systems [1-6], The state of the surfactant molecules in these phases is studied by means of thermal analysis [7,8], DSC is also a useful technique to obtain information about the phase diagrams of surfactant-based systems and the various microstructures formed in these systems. The properties that can be obtained from DSC for binary systems are the following [6] ... 

The gel-liquid crystal transition in surfactant-based systems is the result of the cooperative melting of the hydrocarbon chains [58]. The melted state in a surfactant-based system is less disordered than that of liquid hydrocarbons due to the anchoring of one end of the molecule to the microstructure surface via its polar headgroup. This transition can be sharp in pure synthetic phospholipids and surfactants, but it is broad and ill-defined in natural phospholipids and surfactants, which are usually mixtures with a variety of hydrocarbon chain lengths. The transition temperature, T, depends on the nature of the polar headgroup and the... 

The hydrocarbon chain melting in surfactant-based systems may give rise to the formation of liquid crystals or molecular or micellar solutions, depending on concentration. The addition of water to surfactant decreases and the enthalpy associated with the transition. This is probably due to a reduction in the cohesion of the polar headgroup network. The effect is especially strong in transitions from solid to solid plus liquid crystals. In pure dioctadecyldimethylammonium bromide (DODAB), the polar layer melts at 86.5°C with a A// of 130 J/g. The transition temperature decreases as water content increases and disappears at about 75% DODAB. At this point, the gel-liquid crystal transition happens at a temperature that is independent of water content [46]. 

VIII. THE STATE OF WATER IN SURFACTANT-BASED SYSTEMS... 

One of the principal components of surfactant-based systems is water, which is often neglected, and sometimes only the melting point of this component in the system is reported. The behavior of water is sensitive to the presence of adjacent interfaces of different types, such as biomembranes, proteins, and inorganic compounds [170]. Properties of water molecules depart considerably from their average bulk values when there are solutes or interfaces in the neighborhood. Water in very small volumes plays a dominant role as the medium that controls structure, function, dynamics, and thermodynamics near biological membranes or in other confined regions of space [171]. 

Further development of recovery methods contemplated physical and chemical procedures, such as application of pressure, water injection, or implementation of techniques that alter system miscibility. All aspects that impact on the flnal recovery yield must be considered, for example capillary forces oil viscosity contact angle between the adsorbed oil and the solid surface permeability, wettability, and porosity of the solid reservoir among others. Hence, it is obvious that huge perturbations are provoked in the oil reservoirs when surfactant-based systems are used in enhanced oil recovery operations. The potential role of microemulsions in such activities is once again highlighted. 

It is important to understand the mechanism of corrosion inhibition promoted by surfactant-based systems. The transition of the metal-solution interface from an active dissolution state to a passivation state is highly important in petroleum fields. Normally, surfactants are added to aqueous media to occupy the interface, hence reducing corrosion of the pipelines. It is known that increasing surfactant concentrations reduce interfacial tensions, as a result of enhanced aggregation and physical adsorption upon micelle formation at concentrations above the CMC. 

Ribeiro Neto, V. C. 2007. Development of surfactant-based systems for petroleum enhanced recovery, M.Sc. dissertation, PPGEQ, Chemical Engineering Department, UFRN, Brazil (in Portuguese). 

When oil is recovered from sedimentary formations by conventional means, more than one-half of it can be left behind in the rock (48). This oil is very difficult to remove because it is coating the rock surfaces and not free-flowing. Surfactant-based systems have been developed to enhance the recovery of the trapped oil. When these surfactant solutions are pumped underground, they appear to form microemulsions, bicontinuous structures, and possibly very fine macroemulsions, with the oil. The flow properties of these emulsions through porous media are quite important, therefore much elfort has been invested in rheological studies (49). Once the emulsified oil is removed from the ground, the emulsion needs to be broken in order for the oil to be recovered from the process stream. Another application of emulsions in the petroleum industry is to produce relatively low viscosity emulsions of viscous crude oil to make pipeline transport much easier. 

In this chapter some problems connected with the utilization of subzero temperature differential scanning calorimetry (SZT-DSC) are discussed. Among them are the determination of hydration numbers of surfactants and organic compounds, the determination of the hydration shell thickness, the effect of alcohol on the distribution of water between free and bound states in nonionic surfactant-based systems, and some considerations regarding the problem of phase separation of such systems in subzero temperatures. The signihcance of SZT-DSC for some novel applications is also discussed. 

The aim of this chapter is to present the basic considerations and concepts germane to the use of SZT-DSC for the investigation of water behavior in surfactant-based systems and to relate them to some already established applications of microemulsions. 

Three types of water behavior in surfactant-based systems were observed. 

The close agreement with Aw/eo = 3 obtained for the quaternary system A might prima facie lead us to conclude that the degree of hydration in surfactant-based systems depends on neither the length of the hydrophilic head group of the ethoxylated surfactant nor the presence of pen-tanol (or dodecane) [2,11],... 

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