Abstract:

Surface tension is an important physical property of fluid. The methods for measuring surface tension usually include capillary rising method, maximum bubble pressure method, ring method, plate method, spinning drop method and pendant drop method. At present, the most common method to measure surface tension is plate method or ring method as recommended by the national standard. However, as a mature method of surface tension measurement, pendant drop method has the functions of static and dynamic surface tension measurement, but it is seldom used. In this work, when the static surface tension of surfactant solution with relatively low concentration was measured by pendant drop method, it was found that the results were quite different from that of ring method, while the data of pure liquids and those surfactant solutions with higher concentrations were essentially in agreement with those results obtained by ring method. In addition, dynamic surface tension measurement was used to explore the reasons for the differences between the two methods in static measurement. The application scope of surface tension measurement by pendant drop method was also summarized. Regarding the accuracy of surface tension test by pendant drop method, the influence of time must be paid close attention to. For the samples of low efficiency to reduce the surface tension, especially at relatively low concentrations, it is recommended to use dynamic surface tension measurement rather than static surface tension measurement. As a mature method, pendant drop method has been applied to the determination of surface tension. Most of the current studies have focused on the determination of pure liquids, and most of them are static determination. In practical applications, surfactant solutions are multicomponent systems, and sometimes it is necessary to rapidly reduce surface tension at lower concentrations. Therefore, in such kind of research, it is very necessary to use pendant drop method to study dynamic surface tension of the mixed surfactant system. Pendant drop method, as a method with simple operation, less sample amount, rapid determination and accurate results, has both static surface tension and dynamic surface tension measurement, and will be applied to a wider range.

Key words: pendant drop method, dynamic surface tension, surfactant