A novel method of measuring dynamic surface tension from the profile of capillary jet (2nd report, measurement of dynamic surface tension)

A novel measuring method for dynamic surface tension of surfactant aqueous solutions is proposed. In this method, the dynamic surface tension is measured by comparing the trajectory of a free laminar liquid jet ejected horizontally from a circular orifice to a theoretical trajectory. The theoretical trajectory is obtained by solving ordinary differential equations, which is conducted from momentum balances between inertial force, surface tension, gravitational force and pressure. Circular cross section and simplified pressure distribution in the liquid jet are assumed in the theoretical analysis. Surface tension affects the trajectory of the horizontal jet with inertial force and gravitational force under the condition of Weber number We≈1 and Bond number Bo≈1, whereas viscous force is negligible because the order of capillary number is 10 -3 under the experimental condition of this study. The experimental trajectory is obtained by photography. The experimental trajectory is compared with a theoretical trajectory calculated at an assumed surface tension, and the theoretical trajectory in agreement with the experimental trajectory gives the time varying surface tension (dynamic surface tension) of liquid. The obtained dynamic surface tensions of several kinds of surfactant aqueous solutions by. this method agree well with ones measured by conventional oscillating jet method and maximum bubble pressure method. This agreement proves the validity of this method.