AN ANALYSIS OF THE FACTORS AFFECTING DYNAMIC TENSION MEASUREMENTS WITH THE PULSATING BUBBLE SURFACTOMETER

The pulsating bubble surfactometer (PBS) measurement of surface tension from the pressure difference across the air/water interface and the bubble radius is analyzed theoretically. Sample calculations indicate that deformation of small bubbles due to gravity introduces a small error in the PBS measurements. This error can be accounted for. When the bubble is created, induced convection may accelerate the dynamic adsorption of Triton X-100 surfactant solutions. The effects of an inertial term, bulk shear viscosity, gas flow in the connecting capillary, and surface dilatational viscosity on the dynamic pressure response are calculated. Among these factors, only the surface dilatational viscosity may play an important role in the measurements, and it plays a minor role in the examples considered for frequencies less than 100 cycles/min (rpm). The results were applied to new oscillatory data on sodium dodecylsulfate (SDS) and Triton X-100 solutions at 25-degrees-C. In these systems, most or all of the pressure amplitude response is due to surface tension effects. (C) 1994 Academic Press, Inc.