A new experimental method for the measurement of the interfacial tension between immiscible fluids at zero bond number

A new methodology (Pressure Derivative Method) for measuring the interfacial tension σ between immiscible fluid phases at Δ ρg = 0 (zero Bond number) is presented. This method, which is particularly suitable for measurements under microgravity conditions, is also applicable on earth to liquid pairs with a small density difference. The method consists, essentially, of calculating σ by a linear fitting of experimental capillary pressure and curvature data, collected during the formation of a drop of one of the two liquids inside the other one. The curvature data are derived from the injected drop's volume; thus, any pair of fluids can be used, including opaque liquids, for which optical curvature measurements are not possible. By a specific mathematical treatment of the experimental data, an overall accuracy on the order of less than 1% has been obtained. During the drop growth, a maximum in the pressure is reached, which can also be used to calculate σ by the Maximum Bubble Pressure technique (MBP). This value can be utilized as an internal check on the interfacial tension data obtained by the method proposed.