Interracial tension

Inteifacial tension. A high interfacial tension promotes rapid coalescence and generally requires high mechanical agitation to produce small droplets. A low interracial tension allows drop breakup with low agitation intensity but also leads to slow coalescence rates. Interfacial tension usually decreases as solubility and solute concentration increase and falls to zero at the plait point (Fig. 15-10). 

Concerning thermodynamically unstable emulsions, the creation of new interfaces from the disruption of the disperse phase increases the free energy of the system, which tends to return to the original two separate systems. Therefore, the use of emulsifier is necessary not only to reduce the interracial tension, but also to avoid the coalescence and the formation of macroaggregates thanks to electrostatic repulsion between adsorbed emulsifier. 

To establish a correlation between the interracial tension gradient measurements given above with three phase foam stability we used the qualitative Barch method for determining foam stability, due to the physicochemical difficulties in providing an accurate measure of three phase foam stability. 

A series of surfactant formulations were made up, each of which represented type I or type II preference behavior and each of which had an n. value within the "crude oil" range of 6 to 9. The interracial tensions cf each surfactant were measured against each of the crude oils and several of the lower alkanes. 

THE PHYSICO-CHEMICAL CONDITIONS NECESSARY TO PRODUCE ULTRALOW INTERRACIAL TENSION AT THE OIL/BRINE INTERFACE... 

Reduced Surface Tension. Just as surfactants self-organize in the bulk solution as a result of their hydrophilic and hydrophobic segments, they also preferentially adsorb and organize at the solution—vapor interface. In the case of aqueous surfactant solutions, the hydrophobic tails protrude into the vapor and leave only (he hydrophilic head groups in contact with the solution. The favorable energetics of the arrangement can be seen by the reduction in Ihe interracial free energy per unit area, nr surface tension, it. 

The mass-transfer coefficients depend on complex functions of diffu-sivity, viscosity, density, interfacial tension, and turbulence. Similarly, the mass-transfer area of the droplets depends on complex functions of viscosity, interfacial tension, density difference, extractor geometry, agitation intensity, agitator design, flow rates, and interracial rag deposits. Only limited success has been achieved in correlating extractor performance with these basic principles. The lumped parameter H deals directly with the ultimate design criterion, which is the height of an extraction tower. 

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