Surfactant solutions as test liquids for measurement of critical surface tension

Contact angles of various liquids and surfactant solutions on polytef and paraffin were measured. Critical surface tension values were obtained by extrapolation of plots of cosine of the contact angles versus corresponding surface tension values. Contact angles measured using polyoxyethylene octylphenols produced linear Zisman plots and yielded critical surface tensions that agreed with accepted values. This liquid series provides a reasonable approach to the measurement of critical surface tension for solid drugs that are soluble in organic liquids but relatively insoluble in water.