Calculation of contact angles from surfactant adsorption isotherms

Wetting in the system hematite–water–diisobutyl ketone was studied in the presence of an anionic surfactant, hexadecyl sulfonic acid. Adsorption isotherms of surfactant on hematite powder were measured separately at the interfaces between hematite–water and hematite–ketone, and the interfacial tension of the water–ketone interface was determined as a function of surfactant concentration. The Gibbs and Young’s equations were used to calculate contact angles from the adsorption data. For comparison, contact angles were measured as a function of surfactant concentration on the face of a hematite crystal selected from the same supply of specular hematite used for preparing the hematite powder. Overall, contact angles calculated from the equations correlate closely with measured contact angles.

Graphical abstractThermodynamic Model For Contact Angle.Figure optionsDownload full-size imageDownload as PowerPoint slide