Determination of line tension from the drop size dependence of contact angles

Abstract

The drop size dependence of the advancing contact angle of dodecane and ethylene glycol on carefully prepared FC-721, Zonyl FSC and DDOA surfaces has been studied by means of axisymmetric drop shape analysis. The contact angles were measured in air and were found to decrease by 3 to 5 degrees as the radius of the three-phase contact line increased from approximately 1 to 5 mm. This phenomenon is interpreted in terms of line tension by the modified Young equation. Our experimental results show that the line tensions are positive and of the order of 1 μJ m −1 for all the three solid-liquid systems in our study; these results are consistent with previous work in our laboratory. The occasionally observed phenomenon that contact angles increase as the radius of the three-phase contact line increased on less carefully prepared surfaces is ascribed to the corrugation of the three phase contact line.