Interfacial tension measurement by the rotating meniscus

The interfacial tension of some pure liquid-liquid systems was calculated from the shape of a rotating meniscus. This technique is presented as an alternative method to determine the interfacial tension when the liquid-liquid ratio during the test is expected to affect the relative rates of desorption of the surfactant from the interface. The profile of each meniscus has been studied by analysis of each image with the use of a video camera and a computer. The pressure difference across the interface, combined with Laplace's equation was used to obtain the general differential equation. The approach developed by Bashforth and Adams and extended by Sugden was used to obtain, for the first time, a real value of the ratio of curvature at the apex. This parameter was necessary to obtain an approximation of the solution and thus the interfacial tension for each system. A computer program and a mathematical convergence method were used to reach the solution. The values obtained were comparable with the calculated data according to the theoretical equation of Fowkes and the values reached by other experimental techniques. Ultra low interfacial tensions have been obtained from crude oil/alkaline solutions systems too. The possibility of studying the interfacial rheological behavior using this technique has been analyzed (C) 2000 Elsevier Science B.V. All rights reserved.