Hydrodynamic processes in dynamic bubble pressure experiments 2. Slow meniscus oscillations

The physical mechanisms of processes taking place immediately after a bubble separates from a capillary are discussed. The decreased pressure inside a separating bubble and at the orifice of the capillary cause the movement of liquid into the capillary. The depth of this displacement is limited by the kinetics of changes in gas pressure along the capillary. When the gas pressure becomes equal to the meniscus capillary pressure, the meniscus starts to move back to the capillary tip. Equations are derived which describe the restoration process of a quasistationary pressure distribution along the capillary. A solution of these equations is obtained which describes the evolution of pressure distribution along the capillary with time. Even in the ms time range, the characteristic time of quasistationary pressure distribution re-establishment along the capillary is shown to be shorter than the time necessary to overcome the maximum bubble pressure. The existence of fast oscillations in gas pressure in short capillaries is also predicted. In this case, the characteristic time is found to be comparable to the hydrodynamic relaxation time. (C) 1998 Elsevier Science B.V.