Interfacial tension affected

Sodium lauryl sulfate is often used in medicinal preparations. As mentioned above, it is used as an emulsifer for creams and lotions in cosmetic preparations, but due to its low toxicity and biological compatibility it is also used in the preparation of creams, gels, and emulsions in which the medications are dispersed. Its ability to lower the interfacial tension affects the potentiation and availability of medications. 

There are usually many candidate solvents for any particular application. Important factors to consider are (1) the affinity of the solute for the solvent (i.e., its distribution coefficient should be large) (2) the affinity of other species in the mixture for the solvent (i.e., their distribution coefficients should be small) (3) solvent safety considerations (e.g., flammability and toxicity) (4) solvent handling properties such as density, viscosity, and vapor pressure (5) solvent solubility in the raffinate phase (high solubilities may translate into high solvent losses unless steps are taken to prevent such losses) and (6) solvent cost. In addition, liquid-liquid interfacial tension affects the interfacial area and the rate of mass transfer between the phases. 

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. 

Atomization. A gas or Hquid may be dispersed into another Hquid by the action of shearing or turbulent impact forces that are present in the flow field. The steady-state drop si2e represents a balance between the fluid forces tending to dismpt the drop and the forces of interfacial tension tending to oppose distortion and breakup. When the flow field is laminar the abiHty to disperse is strongly affected by the ratio of viscosities of the two phases. Dispersion, in the sense of droplet formation, does not occur when the viscosity of the dispersed phase significantly exceeds that of the dispersing medium (13). 

Adsorption onto Particles. The Gibbs Adsorption Law relates how adsorption (qv) onto surfaces affects interfacial tension,... 

Properties of Component Phases As discussed in the preceding subsection, dispersions of gases in liquids are affected by the viscosity of the hquid, the density of the liquid and of the gas, and the interfacial tension between the two phases. They also may be affected directly by the composition of the hquid phase. Both the formation of bubbles and their behavior during their lifetime are influenced by these quantities as weh as by the me(manical aspects of their environment. 

The mechanism of droplet deformation can be briefly summarized as follows. The factors affecting the droplet deformation are the viscosity ratio, shear stress, interfacial tension, and droplet particle size. Although elasticity takes an important role for general thermoplastics droplet deformation behavior, it is not known yet how it affects the deformation of TLCP droplet and its relationship with the processing condition. Some of... 

A study on a commonly used demulsifier, namely, a phenol-formaldehyde resin, elucidated how various parameters such as interfacial tension, interfacial shear viscosity, dynamic interfacial-tension gradient, dilatational elasticity, and demulsifier clustering affect the demulsification effectiveness [1275]. 

Water Uptake. There is evidence to suggest that water uptake caused by capillary forces is the crucial factor in the disintegration process of many formulations. In such systems the pore structure of the tablet is of prime importance and any inherent hydrophobicity of the tablet mass will adversely affect it. Therefore, disintegrants in this group must be able to maintain a porous structure in the compressed tablet and show a low interfacial tension towards aqueous fluids. Rapid penetration by water throughout the entire tablet matrix to facilitate its breakup is thus achieved. Concentrations of disintegrant that ensure a continuous matrix of disintegrant are desirable and levels of between 5 and 20% are common. 

The presence of electrical charge affects the interfacial tension in the interphase. If one of the phases considered is a metal and the other is an electrolyte solution, then the phenomena accompanying a change in the interfacial tension are included under the term of electrocapillarity. 

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. 

The units of interfacial tension are identical for surface tension, i.e., dyn/cm. Interfacial tension values of organic compoimds range from zero for completely miscible liquids (e.g., acetone, methanol, ethanol) up to the surface tension of water at 25 °C which is 72 dyn/cm (Lyman et al., 1982). Interfacial tension values may be affected by pH, surface-active agents, and dissolved gases (Schowalter, 1979). Most of the interfacial tension values reported in this book were obtained from Dean (1987), Demond and Lindner (1993), CHRIS (1984), and references cited therein. 

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]. 

---