The effect of viscosity on the relaxation time for surface tension measurement*

In this study, the effect of viscosity, of a test liquid on static and dynamic surface tension measurements, is scrutinized for three widely used techniques. For every surface tension measurement technique, formation and destruction of the interface are paramount to determine the force per unit quantification. Forming or destructing the interface is a dynamic process, and the time scale to create the equilibrium interface depends on the measurement technique's working principle. In the case of the pendant drop, the appropriate generation of the hanging drop is required to achieve the acceptable shape factor. Without this acceptance, the correct surface tension value cannot be extracted from the images. Similarly, for non-image-based techniques, as in Bubble pressure and Wilhelmy plate, the formation of the desired interface shape is required to obtain correct and precise surface tension quantification. Thus, appropriate interface shape formation is a dynamic process and irrespective of measurement technique it is an imperative step. Most characterizing liquids have their response time governed by the viscous nature of the liquid. Here we attempted to comment on the viscous relaxation time that one has to consider to obtain the correct surface or interfacial tension measurements.