时间效应在悬滴法测定表面张力中的影响

Discussion on the time effect in surface tension measurement by pendant drop method

表面张力是流体重要的物理性质,测定表面张力的方法通常包括毛细管上升法、最大气泡压力法、拉环法、旋滴法和悬滴法等。目前,最普遍的表面张力的测定方法为国家标准推荐的平板法或拉环法。然而,悬滴法作为一项成熟的表面张力测定方法且具备静态表面张力及动态表面张力测定功能,目前使用该法测定的较少。文章使用悬滴法测定较低含量的表面活性剂溶液静态表面张力时发现结果与拉环法差异较大,而测定单组分液体及含量较大的表面活性剂溶液,悬滴法与拉环法的测定数据差异较小,这种情况的相关报道较少。另外,使用动态表面张力测定探索了静态测定时出现差异的原因,并对应用悬滴法进行表面张力测定的适用范围进行了总结。使用悬滴法测定表面张力时,应注意时间效应的影响。

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.