Interfacial tension ionic strength effects

With increasing ionic strength, the solubility of the monomer increases. At constant temperature, this is attributed entirely to a decrease in interfacial tension. The temperature effect is on both the monomer-water interaction and on the interfacial tension [141]. 

The electrolyte concentration also has an effect on the co-areas. An increase in the ionic strength from 0.01 to 0.04 M causes a considerable decrease in the interfacial tension [56]. 

Since then, the depletion of ions from the air/water interface became the commonly accepted representation of the surface tension of electrolyte solutions. However, this common picture is not always true near a charged interface, there is an accumulation of counterions, predicted by the Poisson—Boltzmann treatment, which at very low electrolyte concentrations (less than 1CT3 M) can dominate the interfacial depletion of ions due to ion hydration forces,6 and consequently, the surface tension of aqueous electrolytes can decrease with increasing ionic strength (The Jones-Ray effect).7 Even more significant, the surface tension of acids decreases with increasing... 

In Fig. 10 the interfacial tension and the stability of concentrated emulsions containing styrene and an aqueous sodium chloride solution are plotted against the concentration of sodium chloride. The w/o concentrated emulsions are stable for both Span 20 and Span 80. When SDS was used as surfactant, the o/w concentrated emulsions were more unstable at 50 °C than the above w/o concentrated emulsions because the double layer repulsion between cells is shielded by the high ionic strength. With SDS, concentrated emulsions did not form at room temperature above a salt concentration of 1.2 moll-1 because of the salting-out effect. The o/w concentrated emulsion did not form at all at 25 °C when Span 20 was employed as surfactant. 

Surfactant Mixing Rules. The petroleum soaps produced in alkaline flooding have an extremely low optimal salinity. For instance, most acidic crude oils will have optimal phase behavior at a sodium hydroxide concentration of approximately 0.05 wt% in distilled water. At that concentration (about pH 12) essentially all of the acidic components in the oil have reacted, and type HI phase behavior occurs. An increase in sodium hydroxide concentration increases the ionic strength and is equivalent to an increase in salinity because more petroleum soap is not produced. As salinity increases, the petroleum soaps become much less soluble in the aqueous phase than in the oil phase, and a shift to over-optimum or type H(+) behavior occurs. The water in most oil reservoirs contains significant quantities of dissolved solids, resulting in increased IFT. Interfacial tension is also increased because high concentrations of alkali are required to counter the effect of losses due to alkali-rock interactions. 

The direct relation he assumed between ionization and interfacial tension seems reasonable in the light of more recent work, and the effect, now believed to depend on the ionic strength of the aqueous solution, was certainly real. The results of surface potential of fatty acid films, measured by Schulman (71), also confirm qualitatively his finding. 

The effective interfacial area a " is increased by increases in ionic strength, ion valence number, or viscosity, by the presence of a solid or immiscible liquid, and by a decrease in liquid surface tension. Thus it is nearly impossible to predict a priori the interfacial area. However, scale-up is practicable from experiments carried out with the actual gas-liquid system in a small agitated contactor (D = 10-20 cm). The experimental work of Sharma et al. (M12, S23) shows that a scale-up basis of equal ndf,/ /D or n - n dJwD (when djD = 0.4-0.5) can be used with a fair degree of confidence (respectively, 10 and 16% average deviations) for agitated vessels with diameters up to 60 cm. 

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