Surface Between Water and Another Liquid

An important quantity in this regards is the interfacial tension between the two liquids. Freitas et al. (1997) compiled a comprehensive list of yws values for the surface tension between water and immiscible Uquids S mostly at 20 °C or exceptionally at temperatures between 19 and 26 °C. Representative values are shown in Table 4.1. The larger the mutual solubility of water with the liquid S the smaller is the interfacial tension, until it vanishes, of course, for water-miscible liquids. Tri-ethylamine is a case in point, since at 20 °C with yws = 0.1 mN m it is just 2 °C above the upper consolute temperature. 

The interfacial tension is related to the work of adhesion between the two phases per unit surface area, Wws, by  

This work, on the other hand, is empirically related to the Ostwald coefficient Lsw for the solubility of the organic liquid as a gaseous solute in water, Lsw = cs-in-w/cs-gas. 

Another way of looking at the surface tension between two liquids, in the present context between water and an immiscible liquid S, is in terms of the spreading coefficient of S, Ssw- 

When a drop of a liquid with small ys, such as benzene and long chain alcohols, is placed on water it is expected to spread, Asw 0, but for liquids such as CS2 

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