A novel technique for measuring interfacial tension in a binary system

A technique for determining interfacial tension from the shape of axisymmetric fluid-liquid interface is presented. The technique entails using a novel data aquisition method which uses a high speed video camera to record pendant drop images and a standard graphics computer to precisely measure drop edge coordinates.

The interfacial tension is determined by curvefltting the drop edge coordinates to the Laplace equation. Curvefltting is achieved by defining the objective function as the sum of the squared perpendicular distance between the theoretical Laplace curve and the experimental data points. An iterative nonlinear parameter estimation technique (the linearization method) is subsequently used to minimize the objective function by varying key parameters (i.e. X_o and Y_o (apex coordinates), R_o and, the shape factor, β_c). The interfacial tension is obtained from β_c.

Experimental results show that precisions of 1.2-2.5% are achieved in determining interfacial tensions for various liquid-liquid systems. Furthermore, the effect of temperature on the interfacial tension of several systems, and the effect salt on the interfacial tension of water-2-ethyl hexanol are presented