Surfactant interfacial tension affected

Thus, to encourage wetting, 7sl and 7lv should be made as small as possible. This is done in practice by adding a surfactant to the liquid phase. The surfactant adsorbs to both the liquid-solid and liquid-vapor interfaces, lowering those interfacial tensions. Nonvolatile surfactants do not affect 7sv appreciably (see, however. Section X-7). It might be thought that it would be sufficient merely to lower ytv and that a rather small variety of additives would suffice to meet all needs. Actually it is equally if not more important that the surfactant lower 7sL> and each solid will make its own demands. 

The interfacial tension behavior between a crude oil (as opposed to pure hydrocarbon) and an aqueous surfactant phase as a function of temperature has not been extensively studied. Burkowsky and Marx T181 observed interfacial tension minima at temperatures between 50 and 80°C for crude oils with some surfactant formulations, whereas interfacial tensions for other formulations were not affected by temperature changes. Handy et al. [191 observed little or no temperature dependence (25-180°C) for interfacial tensions between California crude and aqueous petroleum sulfonate surfactants at various NaCI concentrations. In contrast, for a pure hydrocarbon or mineral oil and the same surfactant systems, an abrupt decrease in interfacial tension was observed at temperatures in excess of 120°C 1 20]. Non ionic surfactants showed sharp minima of interfacial tension for crude... 

For results where comparisons could be made, the interfacial tension behavior was practically independent of the type of heavy oil used. Interfacial tensions strongly depended on the surfactant type, temperature, and NaCI and CaCI2 concentrations. Changes in the structure of the amphiphile at the oil/water interface is affected by these variables and accounted for some of the experimental observations. 

Kellerhals, G.E. and Chiou, C.S. "Use of Perspective Plots to Aid in Determining Factors Affecting Interfacial Tensions Between Surfactant Solutions and Crude Oil," Soc. Pet. Eng. J.. June 1982, 350-352. 

At low flow velocity of the dispersed phase, the interfacial tension does not influence the droplet diameter but it affects the time-scale parameters for droplet formation [35-37] the detachment time becomes shorter at high interfacial tension (low surfactant concentration) [38]. 

In mixed surfactant systems, physical properties such as the critical micelle concentration (cmc) and interfacial tensions are often substantially lower than would be expected based on the properties of the pure components. Such nonideal behavior is of both theoretical interest and industrial importance. For example, mixtures of different classes of surfactants often exhibit synergism (1-3) and this behavior can be utilized in practical applications ( ).In addition, commercial surfactant preparations usually contain mixtures of various species (e.g. different isomers and chain lengths) and often include surface active impurities which affect the critical micelle concentration and other properties. 

The axial velocity affects the droplet size by both influencing the surfactant mass transfer to the newly formed interface (that speeds up the reduction of the interfacial tension) and the drag force (that pulls droplets away from the pore mouth). 

Adsorption can be measured by direct or indirect methods. Direct methods include surface microtome method [46], foam generation method [47] and radio-labelled surfactant adsorption method [48]. These direct methods have several disadvantages. Hence, the amount of surfactant adsorbed per unit area of interface (T) at surface saturation is mostly determined by indirect methods namely surface and interfacial tension measurements along with the application of Gibbs adsorption equations (see Section 2.2.3 and Figure 2.1). Surfactant structure, presence of electrolyte, nature of non-polar liquid and temperature significantly affect the T value. The T values and the area occupied per surfactant molecule at water-air and water-hydrocarbon interfaces for several anionic, cationic, non-ionic and amphoteric surfactants can be found in Chapter 2 of [2]. 

The fluid-fluid tension and the wettability requirement in turn set limits on the tension between the porous medium and each of the fluids. These fluid-solid interfacial tensions are affected by the isotherm for surfactant adsorption. 

The presence of surfactants, either natural or added, promotes emulsion stability by the reduction of interfacial tension and the formation of highly rigid films on the surface of the droplets. This reduction of interfacial tension can increase the maximum, M, in Figure 4 significantly through charge stabilization or steric stabilization (J5). Because the nature and shape of the interaction energy curve determine the stability of OAV (and other types) of emulsions, any process, parameter, or phenomenon that affects the shape of this curve will ultimately control emulsion stability. 

A lower interfacial tension will lead to a more stable emulsion. Temperature affects physical properties of oil, water, interfacial films, and surfactant solubilities in the oil and water phases, which can all affect emulsion stability. Further, the rheology of the emulsion itself is affected significantly by temperature. 

The presence of a surfactant means that, during emulsification, the interfacial tension need not to be the same everywhere (see Figure 10.17). This has two consequences (i) the equilibrium shape of the drop is affected and (ii) any... 

In most systems, it is of interest to determine how a change in the alkyl part of the organic molecule (i.e., the hydrophobic part) affects the surface and interfacial tension. In spite of its importance (both in biology and technical industry), no such systematic analysis is found in the current literature. These molecular considerations are pertinent in any reaction where the hydrophobicity might be of major importance in the system, e.g., surfactant activity, EOR, protein structure and activity, and pharmaceutical molecules and activity. 

The interfacial tension, o, affects the rate ratio directly only through the capillary pressure, P = 2o/P. The electrolyte primarily affects the electrostatic disjoining pressure, n, which decreases as the salt content increases, thus destabilizing the OAV emulsion. It can also influence the stability by changing the surfactant adsorption (including the case of nonionic surfactants). 

The temperature strongly affects the solubility and surface activity of nonionic surfactants. It is well known that at higher temperature nonionic surfactants become more oil soluble, which favors the W/O emulsion. Thus, solubility may change the type of emulsion formed at the PIT. The surface activity has numerous implications the most important is the change of the Gibbs elasticity, Eq, and the interfacial tension, a. 

Surface active additives (cosurfactants, demulsifiers, etc.), such as fatty alcohols in the case of ionic surfactants, may affect the emulsifier partitioning between the phases and its adsorption, thereby changing the Gibbs elasticity and the interfacial tension. The surface-active additive may also change the surface charge (mainly by increasing the... 

The reduction of the tension at an interface by a surfactant in aqueous solution when a second liquid phase is present may be considerably more complex than when that second phase is absent, i.e., when the interface is a surface. If the second liquid phase is a nonpolar one in which the surfactant has almost no solubility, then adsorption of the surfactant at the aqueous solution-nonpolar liquid interface closely resembles that at the aqueous solution-air interface and those factors that determine the efficiency and effectiveness of surface tension reduction affect interfacial tension reduction in a similar manner (Chapter 2, Section IIIC,E). When the nonpolar liquid phase is a saturated hydrocarbon, both the efficiency and effectiveness of interfacial tension reduction by the surfactant at the aqueous solution-hydrocarbon interface are greater than at the aqueous solution-air interface, as measured by pC2o and IIcmc, respectively. The replacement of air as the second phase by a saturated hydrocarbon increases the tendency of the surfactant to adsorb at the interface, while the tendency to form micelles is not affected significantly. This results in an increase in the CMC/C2o ratio. Since the value of rm, the effectiveness of adsorption (Chapter 2, Section IIIC), is not affected significantly by the presence of the saturated hydrocarbon, the increase in the... 

---