Surface tension regularity of non-polar, polar, and weak electrolyte liquid hydrocarbons

The correlation of reduced surface tension σsc* versus reduced temperature Tsc* which produces family of linear curves is investigated for universality. Each curve is characterized by the reduced temperature index Tindex* which is included in Tsc*. The correlation is based on phenomenological scaling law and consideration of law of corresponding states. The reduced temperature Tsc*, scaled distance from the boiling temperature Tb, has the practical advantage of being independent of critical temperature. The correlation is highly accurate when applied to 10 classes of non-polar, slightly polar, polar, and weak electrolyte liquid hydrocarbons. The slopes of linear curves of each class of liquids at given Tindex*'s are rather constant and a universal regularity among all liquid is very likely, however small differences identify three classes of non-polar, slightly polar, and polar plus weak electrolytes. Consideration of the pervious application to molten alkali halides, molten salts, and molten metals, and considering that the reduced surface entropy Ss*=(∂σsc*/∂Tsc*) is rather constant for all liquid tested, strengthen the idea that σsc*-Tsc* correlation is likely universal.