Effect of surfactant on interfacial gas transfer studied by axisymmetric drop shape analysis-captive bubble (ADSA-CB).

A new method combining axisymmetric drop shape analysis (ADSA) and a captive bubble (CB) is proposed to study the effect of surfactant on interfacial gas transfer. In this method, gas transfer from a static CB to the surrounding quiescent liquid is continuously recorded for a short period (i.e., 5 min). By photographical analysis, ADSA-CB is capable of yielding detailed information pertinent to the surface tension and geometry of the CB, e.g., bubble area, volume, curvature at the apex, and the contact radius and height of the bubble. A steady-state mass transfer model is established to evaluate the mass transfer coefficient on the basis of the output of ADSA-CB. In this way, we are able to develop a working prototype capable of simultaneously measuring dynamic surface tension and interfacial gas transfer. Other advantages of this method are that it allows for the study of very low surface tensions (<5 mJ/m2) and does not require equilibrium of gas transfer. Consequently, reproducible experimental results can be obtained in a relatively short time. As a demonstration, this method was used to study the effect of lung surfactant on oxygen transfer. It was found that the adsorbed lung surfactant film shows a retardation effect on oxygen transfer, similar to the behavior of a pure DPPC film. However, this retardation effect at low surface tensions is less than that of a pure DPPC film.