Experimental Confirmation of the Oscillating Bubble Technique with Comparison to the Pendant Bubble Method: The Adsorption Dynamics of 1-Decanol

✍ Scribed by David O. Johnson; Kathleen J. Stebe

• Book ID: 102575568
• Publisher: Elsevier Science
• Year: 1996
• Tongue: English
• Weight: 261 KB
• Volume: 182
• Category: Article
• ISSN: 0021-9797
• DOI: 10.1006/jcis.1996.0497

✦ Synopsis

sorb onto the interface. In a previous paper, a theory was A new oscillating bubble method is used to measure surfactant presented which allows the measurement of surfactant diffumass transfer kinetics at liquid-gas interfaces. A spherical bubble is sion and adsorption kinetics using the controlled oscillations formed, equilibrated, and oscillated radially with a small amplitude. of a spherical bubble at the end of a capillary (1). In this The radial oscillations cause the gas-phase pressure to cycle about paper, experimental results for the oscillating bubble method its equilibrium because of the periodic changes in bubble curvature for aqueous 1-decanol solutions are presented.

and surface tension. The phase angle u between the radial and the

In the method, a spherical bubble is formed and equilipressure oscillations and the amplitude ratio of these two quantities brated at the tip of a needle immersed in surfactant solution.

are measured as a function of forcing frequency v and concentration C (0) . These data are analyzed according to a linear analysis presented The bubble is forced to oscillate with a frequency v by in part I of this research (J. Colloid Interface Sci. 168, 21, 1994) to periodically injecting and withdrawing a small volume of find surfactant diffusivities and adsorption/desorption coefficients. gas. The periodic surface expansion causes the surface ten-The required input data are the equilibrium adsorption isotherm and sion to cycle about its equilibrium value. However, the surthe corresponding surface equation of state. For 1-decanol at the airface tension is out of phase with the radius because of hinaqueous interface, equilibrium surface tension data are obtained by dered adsorption/desorption and diffusion. The radial oscilvideo-enhanced pendant bubble tensiometry and fitted to the generallation also creates a flow field which perturbs the liquidized Frumkin model. The oscillating bubble method is then used to phase pressure. All of these contribute to oscillations in the determine the mass transfer kinetics of 1-decanol. For v £ 1 rad/ gas-phase pressure, which is therefore out of phase with the s, the mass transfer is diffusion-controlled. Diffusivities found from radius.

the oscillating bubble data are in agreement with those obtained from pendant bubble relaxation data. For elevated C (0) and v § 1.0 rad/ Assuming that mass transfer to the interface is controlled s, the mass transfer is controlled by both diffusion and the kinetics by both diffusion and adsorption/desorption, and performing of adsorption-desorption. A mixed diffusion-kinetic model applied a linear analysis of the equations of mass transfer and fluid to these data yields a value for the desorption kinetic constant of a dynamics about an equilibrium, quiescent base state, the Å 2.7 s 01 . These results are consistent with the shift in controlling phase angle and the amplitude ratio between the gas-phase mechanism from pure diffusion control at dilute concentrations to pressure and the bubble radius can be related to the physicomixed diffusion-kinetic control at elevated concentrations. ᭧ 1996 chemical parameters in the surfactant system, i.e., the fluid Academic Press, Inc.

viscosity m and density r, and the surfactant mass transfer