Dynamics of expanding foam films under additionally applied pressure

A new drainage model was applied to expanding and draining foam films, which were exposed to an additional pressure, generated by a special nano-pump, except the capillary one. The foam films, prepared from 10−4 M aqueous solution of tetraethylene glycol octyl ether C8E4 + 10−5 M NaCl, were formed in Scheludko cell. A double-concaved drop in the film holder of the Scheludko cell was positioned. The tips of the drop were approached toward each other by sucking out liquid from the side of the meniscus with a given volumetric flow rate by nano-pump controlled by PC. After formation of the foam film the nano-pump was left to continue working. The latter made the film expand with a certain rate until reaching a critical size, where it stopped expanding. The experiment was performed with different volumetric flow rates of the nano-pump in the range of 100 nL/s–10,000 nL/s. A fitting procedure with only one matching parameter – the additional pressure, was performed giving good agreement with the experimental data. A correlation curve speed of nano-pump – additional pressure was determined. The speed of film expanding at each particular case was measured and an empiric equation: expanding rate vs. additional pressure was suggested. In addition, the dependence critical film radius vs. additional pressure was obtained as well.The current experiment aimed at imitating the process of collision between bubbles at foam agitation. It indicated that the shear stresses generated by agitation make the bubbles collide with different speeds forming variety of bubble contact areas.

Figure optionsDownload as PowerPoint slideResearch highlights▶ Bubbles coalesce when their Weber number is lower than the critical one. ▶ Bubbles bounce when their Weber number is larger than the critical one. ▶ The foam films respond with draining and expanding due to a certain external driving force.