Solution/air interfaces I. An oscillating jet relative method for determining dynamic surface tensions

Abstract

The oscillating jet method has been investigated for the determination of the surface tension of water using horizontal jets from elliptical orifices in bell-shaped and uniform-channel tubes. Improved techniques have been developed for measuring the wave parameters, the flow rate and for extending the range of investigations to include the initial 80–90 msec of jet surface age. The surface tension values, calculated using the Bohr equation from measurements on successive waves of the water jets, were dependent on the characteristics of the orifice, its position, the flow rate and the wave serial number, but were within ±2 mN/m of the equilibrium value if the initial wave values were disregarded. An extension of the Bohr equation developed for vertical jets was found to be invalid for horizontal jets. Calculated surface tension versus surface age relationships for surfactant solutions also varied with the experimental conditions, but by fixing the position of the orifice tube, and standardizing with water, a relative method was developed for determining dynamic tensions that were independent of the tube used and of the flow rate. The validity of the method was illustrated by results obtained with two surfactant solutions using seven tubes (bell-shaped and uniform-channel) over an age range from 0.6 to 75 msec. The surface tensions of deionized water samples have been determined by the relative method and compared with those obtained by a static method. The true surface age along the jet surface is concluded to be close to the value derived from the mean axial velocity. Evidence is given indicating that, within the millisecond age range, water does not have a dynamic tension above the equilibrium value.